| Message ID | 1249674197-1065-7-git-send-email-jlayton@redhat.com |
|---|---|
| State | New |
| Headers | show |
Jeff, I'm sorry for a late response. I see two possible issues with resolving ip to hostname and using it as service principal: 1. In case of spoofed revers lookup or local dns cache or compromised dns server or router between client and dns server, we could be connected to a fake server without even noticing it. If we leave code as it is now, i.e. use hostname supplied by user at mount time, we will get service ticket for server we intended to connect to. In this case we at least will get error message in logs "Unexpected SMB signature". As I can remember, the current cifs code only checks signature but doesn't tears session with wrong signature on packets (transport.c:789) and doesn't do mutual authentication of the peer. 2. It will break working now code In environments where there is no dns or revers lookup doesn't match with a supplied server name. And user will not even suspect why cifs doesn't work anymore. PS: Theoretically we could have uninitialized memory read of hostbuf if there wasn't ipv6 or ipv4 parameter in the upcall request. On Fri, Aug 7, 2009 at 11:43 PM, Jeff Layton<jlayton@redhat.com> wrote: > Instead of using the hostname given by the upcall to get the server's > principal, take the IP address given in the upcall and reverse resolve > it to a hostname. > > Signed-off-by: Jeff Layton <jlayton@redhat.com> > --- > client/cifs.upcall.c | 68 +++++++++++++++++++++++++++++++++++++++++--------- > 1 files changed, 56 insertions(+), 12 deletions(-) > > diff --git a/client/cifs.upcall.c b/client/cifs.upcall.c > index 38be876..1e58503 100644 > --- a/client/cifs.upcall.c > +++ b/client/cifs.upcall.c > @@ -150,15 +150,15 @@ handle_krb5_mech(const char *oid, const char *principal, DATA_BLOB *secblob, > #define DKD_HAVE_HOSTNAME 0x1 > #define DKD_HAVE_VERSION 0x2 > #define DKD_HAVE_SEC 0x4 > -#define DKD_HAVE_IPV4 0x8 > -#define DKD_HAVE_IPV6 0x10 > -#define DKD_HAVE_UID 0x20 > -#define DKD_HAVE_PID 0x40 > -#define DKD_MUSTHAVE_SET (DKD_HAVE_HOSTNAME|DKD_HAVE_VERSION|DKD_HAVE_SEC) > +#define DKD_HAVE_IP 0x8 > +#define DKD_HAVE_UID 0x10 > +#define DKD_HAVE_PID 0x20 > +#define DKD_MUSTHAVE_SET (DKD_HAVE_IP|DKD_HAVE_VERSION|DKD_HAVE_SEC) > > static struct decoded_args { > int ver; > char *hostname; > + char *ip; > uid_t uid; > pid_t pid; > sectype_t sec; > @@ -167,6 +167,7 @@ static struct decoded_args { > static unsigned int > decode_key_description(const char *desc, struct decoded_args *arg) > { > + int len; > int retval = 0; > char *pos; > const char *tkn = desc; > @@ -174,7 +175,6 @@ decode_key_description(const char *desc, struct decoded_args *arg) > do { > pos = index(tkn, ';'); > if (strncmp(tkn, "host=", 5) == 0) { > - int len; > > if (pos == NULL) > len = strlen(tkn); > @@ -186,10 +186,18 @@ decode_key_description(const char *desc, struct decoded_args *arg) > arg->hostname = SMB_XMALLOC_ARRAY(char, len); > strlcpy(arg->hostname, tkn + 5, len); > retval |= DKD_HAVE_HOSTNAME; > - } else if (strncmp(tkn, "ipv4=", 5) == 0) { > - /* BB: do we need it if we have hostname already? */ > - } else if (strncmp(tkn, "ipv6=", 5) == 0) { > - /* BB: do we need it if we have hostname already? */ > + } else if (!strncmp(tkn, "ip4=", 4) || > + !strncmp(tkn, "ip6=", 4)) { > + if (pos == NULL) > + len = strlen(tkn); > + else > + len = pos - tkn; > + > + len -= 3; > + SAFE_FREE(arg->ip); > + arg->ip = SMB_XMALLOC_ARRAY(char, len); > + strlcpy(arg->ip, tkn + 4, len); > + retval |= DKD_HAVE_IP; > } else if (strncmp(tkn, "pid=", 4) == 0) { > errno = 0; > arg->pid = strtol(tkn + 4, NULL, 0); > @@ -288,6 +296,35 @@ cifs_resolver(const key_serial_t key, const char *key_descr) > return 0; > } > > +static int > +ip_to_fqdn(const char *ipaddr, char *host, size_t hostlen) > +{ > + int rc; > + struct addrinfo hints = { .ai_flags = AI_NUMERICHOST }; > + struct addrinfo *res; > + > + rc = getaddrinfo(ipaddr, NULL, &hints, &res); > + if (rc) { > + syslog(LOG_DEBUG, "%s: failed to resolve %s to ipaddr: %s", > + __func__, ipaddr, > + rc == EAI_SYSTEM ? strerror(errno) : gai_strerror(rc)); > + return rc; > + } > + > + rc = getnameinfo(res->ai_addr, res->ai_addrlen, host, hostlen, > + NULL, 0, NI_NAMEREQD); > + freeaddrinfo(res); > + if (rc) { > + syslog(LOG_DEBUG, "%s: failed to resolve %s to fqdn: %s", > + __func__, ipaddr, > + rc == EAI_SYSTEM ? strerror(errno) : gai_strerror(rc)); > + return rc; > + } > + > + syslog(LOG_DEBUG, "%s: resolved %s to %s", __func__, ipaddr, host); > + return 0; > +} > + > static void > usage(void) > { > @@ -306,6 +343,7 @@ int main(const int argc, char *const argv[]) > long rc = 1; > int c; > char *buf, *princ, *ccname = NULL; > + char hostbuf[NI_MAXHOST]; > struct decoded_args arg = { }; > const char *oid; > > @@ -383,12 +421,18 @@ int main(const int argc, char *const argv[]) > } > } > > + if (have & DKD_HAVE_IP) { > + rc = ip_to_fqdn(arg.ip, hostbuf, sizeof(hostbuf)); > + if (rc) > + goto out; > + } > + > // do mech specific authorization > switch (arg.sec) { > case MS_KRB5: > case KRB5: > /* for "cifs/" service name + terminating 0 */ > - datalen = strlen(arg.hostname) + 5 + 1; > + datalen = strnlen(hostbuf, sizeof(hostbuf)) + 5 + 1; > princ = SMB_XMALLOC_ARRAY(char, datalen); > if (!princ) { > rc = 1; > @@ -405,7 +449,7 @@ int main(const int argc, char *const argv[]) > * getting a host/ principal if that doesn't work. > */ > strlcpy(princ, "cifs/", datalen); > - strlcpy(princ + 5, arg.hostname, datalen - 5); > + strlcpy(princ + 5, hostbuf, datalen - 5); > rc = handle_krb5_mech(oid, princ, &secblob, &sess_key, ccname); > if (rc) { > memcpy(princ, "host/", 5); > -- > 1.6.0.6 > > _______________________________________________ > linux-cifs-client mailing list > linux-cifs-client@lists.samba.org > https://lists.samba.org/mailman/listinfo/linux-cifs-client >
On Sun, 16 Aug 2009 02:59:24 +0400 "Q (Igor Mammedov)" <qwerty0987654321@mail.ru> wrote: > Jeff, > I'm sorry for a late response. > > I see two possible issues with resolving ip to hostname and using it > as service principal: > 1. In case of spoofed revers lookup or local dns cache or > compromised dns server or router between client and dns > server, we could be connected to a fake server without even > noticing it. I have a hard time understanding this one. I don't think that we gain any security by not trusing reverse hostname resolution. Why? Because you still have to trust the forward resolve to give you the correct address. You're just as likely to end up on a compromised server that way. > If we leave code as it is now, i.e. use hostname > supplied by user at mount time, we will get service ticket for > server we intended to connect to. Only if you use the canonical hostname of the server when mounting. > In this case we at least will > get error message in logs "Unexpected SMB signature". > As I can remember, the current cifs code only checks signature > but doesn't tears session with wrong signature on packets > (transport.c:789) and doesn't do mutual authentication of the peer. > That should probably be fixed sometime, but again, I don't see how you're protected by not trusting reverse hostname resolution. With the previous scheme you *had* to mount with a hostname anyway, so you more or less have to trust your forward resolution anyway. I don't see how trusting reverse resolution increases your security exposure. There's a huge problem with the current scheme however. You need to know the canonical name of the host in the service ticket and then mount that. This is a huge source of confusion for users. Suppose I have a host: server.example.com ...and I have a principal that I need to get in order to mount it: cifs/server.example.com@EXAMPLE.COM ...now, suppose I try to mount up a share from that host, but use a non-canonical hostname in the server section of the UNC: //server/share ...it doesn't work. The upcall will try to assemble a principal name like: cifs/server@EXAMPLE.COM ...similar problem if I try to mount a CNAME for the server. This is also a problem when you want to mix krb5 and DFS. I don't believe the current code sets the hostname. The patch below fixes this (assuming you have your DNS and service principals set up correctly). > 2. It will break working now code In environments where there > is no dns or revers lookup doesn't match with a supplied > server name. And user will not even suspect why cifs doesn't > work anymore. > What about those people who are broken now? I consider the fact that you can't mount using an alternate server hostname a bug. I don't think it's unreasonable to expect that people with a functional krb5 environment also have functioning hostname resolution. I think it's more reasonable to expect that host resolution work than to insist that people use the canonical hostname of the server when mounting. A user may not even have any idea what that hostname actually *is*. We should however probably note that properly functioning reverse host resolution is required in the manpage however (the manpage is due for some work anyway). > PS: > Theoretically we could have uninitialized memory read of > hostbuf if there wasn't ipv6 or ipv4 parameter in the upcall > request. > I don't think so. The patch below also changes: #define DKD_MUSTHAVE_SET (DKD_HAVE_IP|DKD_HAVE_VERSION|DKD_HAVE_SEC) ...or am I missing something? > On Fri, Aug 7, 2009 at 11:43 PM, Jeff Layton<jlayton@redhat.com> wrote: > > Instead of using the hostname given by the upcall to get the server's > > principal, take the IP address given in the upcall and reverse resolve > > it to a hostname. > > > > Signed-off-by: Jeff Layton <jlayton@redhat.com> > > --- > > client/cifs.upcall.c | 68 +++++++++++++++++++++++++++++++++++++++++--------- > > 1 files changed, 56 insertions(+), 12 deletions(-) > > > > diff --git a/client/cifs.upcall.c b/client/cifs.upcall.c > > index 38be876..1e58503 100644 > > --- a/client/cifs.upcall.c > > +++ b/client/cifs.upcall.c > > @@ -150,15 +150,15 @@ handle_krb5_mech(const char *oid, const char *principal, DATA_BLOB *secblob, > > #define DKD_HAVE_HOSTNAME 0x1 > > #define DKD_HAVE_VERSION 0x2 > > #define DKD_HAVE_SEC 0x4 > > -#define DKD_HAVE_IPV4 0x8 > > -#define DKD_HAVE_IPV6 0x10 > > -#define DKD_HAVE_UID 0x20 > > -#define DKD_HAVE_PID 0x40 > > -#define DKD_MUSTHAVE_SET (DKD_HAVE_HOSTNAME|DKD_HAVE_VERSION|DKD_HAVE_SEC) > > +#define DKD_HAVE_IP 0x8 > > +#define DKD_HAVE_UID 0x10 > > +#define DKD_HAVE_PID 0x20 > > +#define DKD_MUSTHAVE_SET (DKD_HAVE_IP|DKD_HAVE_VERSION|DKD_HAVE_SEC) > > > > static struct decoded_args { > > int ver; > > char *hostname; > > + char *ip; > > uid_t uid; > > pid_t pid; > > sectype_t sec; > > @@ -167,6 +167,7 @@ static struct decoded_args { > > static unsigned int > > decode_key_description(const char *desc, struct decoded_args *arg) > > { > > + int len; > > int retval = 0; > > char *pos; > > const char *tkn = desc; > > @@ -174,7 +175,6 @@ decode_key_description(const char *desc, struct decoded_args *arg) > > do { > > pos = index(tkn, ';'); > > if (strncmp(tkn, "host=", 5) == 0) { > > - int len; > > > > if (pos == NULL) > > len = strlen(tkn); > > @@ -186,10 +186,18 @@ decode_key_description(const char *desc, struct decoded_args *arg) > > arg->hostname = SMB_XMALLOC_ARRAY(char, len); > > strlcpy(arg->hostname, tkn + 5, len); > > retval |= DKD_HAVE_HOSTNAME; > > - } else if (strncmp(tkn, "ipv4=", 5) == 0) { > > - /* BB: do we need it if we have hostname already? */ > > - } else if (strncmp(tkn, "ipv6=", 5) == 0) { > > - /* BB: do we need it if we have hostname already? */ > > + } else if (!strncmp(tkn, "ip4=", 4) || > > + !strncmp(tkn, "ip6=", 4)) { > > + if (pos == NULL) > > + len = strlen(tkn); > > + else > > + len = pos - tkn; > > + > > + len -= 3; > > + SAFE_FREE(arg->ip); > > + arg->ip = SMB_XMALLOC_ARRAY(char, len); > > + strlcpy(arg->ip, tkn + 4, len); > > + retval |= DKD_HAVE_IP; > > } else if (strncmp(tkn, "pid=", 4) == 0) { > > errno = 0; > > arg->pid = strtol(tkn + 4, NULL, 0); > > @@ -288,6 +296,35 @@ cifs_resolver(const key_serial_t key, const char *key_descr) > > return 0; > > } > > > > +static int > > +ip_to_fqdn(const char *ipaddr, char *host, size_t hostlen) > > +{ > > + int rc; > > + struct addrinfo hints = { .ai_flags = AI_NUMERICHOST }; > > + struct addrinfo *res; > > + > > + rc = getaddrinfo(ipaddr, NULL, &hints, &res); > > + if (rc) { > > + syslog(LOG_DEBUG, "%s: failed to resolve %s to ipaddr: %s", > > + __func__, ipaddr, > > + rc == EAI_SYSTEM ? strerror(errno) : gai_strerror(rc)); > > + return rc; > > + } > > + > > + rc = getnameinfo(res->ai_addr, res->ai_addrlen, host, hostlen, > > + NULL, 0, NI_NAMEREQD); > > + freeaddrinfo(res); > > + if (rc) { > > + syslog(LOG_DEBUG, "%s: failed to resolve %s to fqdn: %s", > > + __func__, ipaddr, > > + rc == EAI_SYSTEM ? strerror(errno) : gai_strerror(rc)); > > + return rc; > > + } > > + > > + syslog(LOG_DEBUG, "%s: resolved %s to %s", __func__, ipaddr, host); > > + return 0; > > +} > > + > > static void > > usage(void) > > { > > @@ -306,6 +343,7 @@ int main(const int argc, char *const argv[]) > > long rc = 1; > > int c; > > char *buf, *princ, *ccname = NULL; > > + char hostbuf[NI_MAXHOST]; > > struct decoded_args arg = { }; > > const char *oid; > > > > @@ -383,12 +421,18 @@ int main(const int argc, char *const argv[]) > > } > > } > > > > + if (have & DKD_HAVE_IP) { > > + rc = ip_to_fqdn(arg.ip, hostbuf, sizeof(hostbuf)); > > + if (rc) > > + goto out; > > + } > > + > > // do mech specific authorization > > switch (arg.sec) { > > case MS_KRB5: > > case KRB5: > > /* for "cifs/" service name + terminating 0 */ > > - datalen = strlen(arg.hostname) + 5 + 1; > > + datalen = strnlen(hostbuf, sizeof(hostbuf)) + 5 + 1; > > princ = SMB_XMALLOC_ARRAY(char, datalen); > > if (!princ) { > > rc = 1; > > @@ -405,7 +449,7 @@ int main(const int argc, char *const argv[]) > > * getting a host/ principal if that doesn't work. > > */ > > strlcpy(princ, "cifs/", datalen); > > - strlcpy(princ + 5, arg.hostname, datalen - 5); > > + strlcpy(princ + 5, hostbuf, datalen - 5); > > rc = handle_krb5_mech(oid, princ, &secblob, &sess_key, ccname); > > if (rc) { > > memcpy(princ, "host/", 5); > > -- > > 1.6.0.6 > > > > _______________________________________________ > > linux-cifs-client mailing list > > linux-cifs-client@lists.samba.org > > https://lists.samba.org/mailman/listinfo/linux-cifs-client > >
On Sun, Aug 16, 2009 at 4:23 AM, Jeff Layton<jlayton@redhat.com> wrote: > On Sun, 16 Aug 2009 02:59:24 +0400 > "Q (Igor Mammedov)" <qwerty0987654321@mail.ru> wrote: > >> Jeff, >> I'm sorry for a late response. >> >> I see two possible issues with resolving ip to hostname and using it >> as service principal: >> 1. In case of spoofed revers lookup or local dns cache or >> compromised dns server or router between client and dns >> server, we could be connected to a fake server without even >> noticing it. > > I have a hard time understanding this one. I don't think that we gain > any security by not trusing reverse hostname resolution. > > Why? Because you still have to trust the forward resolve to give you > the correct address. You're just as likely to end up on a compromised > server that way. No, we are not trusting anyone, may be except KDC a little ;) > >> If we leave code as it is now, i.e. use hostname >> supplied by user at mount time, we will get service ticket for >> server we intended to connect to. > > Only if you use the canonical hostname of the server when mounting. > >> In this case we at least will >> get error message in logs "Unexpected SMB signature". >> As I can remember, the current cifs code only checks signature >> but doesn't tears session with wrong signature on packets >> (transport.c:789) and doesn't do mutual authentication of the peer. >> > > That should probably be fixed sometime, but again, I don't see how > you're protected by not trusting reverse hostname resolution. With the > previous scheme you *had* to mount with a hostname anyway, so you > more or less have to trust your forward resolution anyway. I don't > see how trusting reverse resolution increases your security exposure. I'll try explain more clearly, what I've meant. Providing that we could have compromised dns resolving, we could not trust forward nor reverse resolution, but the goal of attacker is in redirecting us his server. Case 1: using host name A.B.C supplied at mount time 1.1 we have an IP of a fake server because forward resolution was spoofed 1.2 we get a valid session key from KDC for A.B.C Result: we can detect that packets a coming from a fake server, because of an incorrect signature. Case 2: using host name F.A.K.E from revers resolution 2.1 the same attack vector 1.1, i.e. connect to a fake server's IP, and doing revers resolution we are getting host name of a fake server. 2.2 we get a valid session key from KDC for F.A.K.E because of fake server is a member of our domain. Result: attacker forced us to use his server, nobody will even notice it. I prefer using 'case 1' for my files. And if cifs is fixed to drop a session to a fake server, I will like it even more. Case 2 are safe only in a hardened network environment or with a secure dns setup. > There's a huge problem with the current scheme however. You need to > know the canonical name of the host in the service ticket and then > mount that. This is a huge source of confusion for users. Suppose I > have a host: > > server.example.com > > ...and I have a principal that I need to get in order to mount it: > > cifs/server.example.com@EXAMPLE.COM > > ...now, suppose I try to mount up a share from that host, but use a > non-canonical hostname in the server section of the UNC: > > //server/share > > ...it doesn't work. The upcall will try to assemble a principal name > like: > > cifs/server@EXAMPLE.COM I haven't noticed this case because in AD domain, a machine account is registered with a fqdn and a hostname principals. (At least it is so in my company) So I were able to connect to //server/share > ...similar problem if I try to mount a CNAME for the server. This is > also a problem when you want to mix krb5 and DFS. I don't believe the > current code sets the hostname. The same thing, I someone wishes to provide access to a server via CNAMEs, he/she should create corresponding principals on KDC. This way it will not reduce security. > > The patch below fixes this (assuming you have your DNS and service > principals set up correctly). > >> 2. It will break working now code In environments where there >> is no dns or revers lookup doesn't match with a supplied >> server name. And user will not even suspect why cifs doesn't >> work anymore. >> > > What about those people who are broken now? I consider the fact that > you can't mount using an alternate server hostname a bug. > > I don't think it's unreasonable to expect that people with a functional > krb5 environment also have functioning hostname resolution. I think it's > more reasonable to expect that host resolution work than to insist that > people use the canonical hostname of the server when mounting. A user > may not even have any idea what that hostname actually *is*. > > We should however probably note that properly functioning reverse host > resolution is required in the manpage however (the manpage is due for > some work anyway). And maybe force those who hasn't dns at all, for whatever reason, to use it. > >> PS: >> Theoretically we could have uninitialized memory read of >> hostbuf if there wasn't ipv6 or ipv4 parameter in the upcall >> request. >> > > I don't think so. The patch below also changes: > > #define DKD_MUSTHAVE_SET (DKD_HAVE_IP|DKD_HAVE_VERSION|DKD_HAVE_SEC) > > ...or am I missing something? It just caught my eyes. Anyway I would initialized it, just in case. > >> On Fri, Aug 7, 2009 at 11:43 PM, Jeff Layton<jlayton@redhat.com> wrote: >> > Instead of using the hostname given by the upcall to get the server's >> > principal, take the IP address given in the upcall and reverse resolve >> > it to a hostname. >> > >> > Signed-off-by: Jeff Layton <jlayton@redhat.com> >> > --- >> > client/cifs.upcall.c | 68 +++++++++++++++++++++++++++++++++++++++++--------- >> > 1 files changed, 56 insertions(+), 12 deletions(-) >> > >> > diff --git a/client/cifs.upcall.c b/client/cifs.upcall.c >> > index 38be876..1e58503 100644 >> > --- a/client/cifs.upcall.c >> > +++ b/client/cifs.upcall.c >> > @@ -150,15 +150,15 @@ handle_krb5_mech(const char *oid, const char *principal, DATA_BLOB *secblob, >> > #define DKD_HAVE_HOSTNAME 0x1 >> > #define DKD_HAVE_VERSION 0x2 >> > #define DKD_HAVE_SEC 0x4 >> > -#define DKD_HAVE_IPV4 0x8 >> > -#define DKD_HAVE_IPV6 0x10 >> > -#define DKD_HAVE_UID 0x20 >> > -#define DKD_HAVE_PID 0x40 >> > -#define DKD_MUSTHAVE_SET (DKD_HAVE_HOSTNAME|DKD_HAVE_VERSION|DKD_HAVE_SEC) >> > +#define DKD_HAVE_IP 0x8 >> > +#define DKD_HAVE_UID 0x10 >> > +#define DKD_HAVE_PID 0x20 >> > +#define DKD_MUSTHAVE_SET (DKD_HAVE_IP|DKD_HAVE_VERSION|DKD_HAVE_SEC) >> > >> > static struct decoded_args { >> > int ver; >> > char *hostname; >> > + char *ip; >> > uid_t uid; >> > pid_t pid; >> > sectype_t sec; >> > @@ -167,6 +167,7 @@ static struct decoded_args { >> > static unsigned int >> > decode_key_description(const char *desc, struct decoded_args *arg) >> > { >> > + int len; >> > int retval = 0; >> > char *pos; >> > const char *tkn = desc; >> > @@ -174,7 +175,6 @@ decode_key_description(const char *desc, struct decoded_args *arg) >> > do { >> > pos = index(tkn, ';'); >> > if (strncmp(tkn, "host=", 5) == 0) { >> > - int len; >> > >> > if (pos == NULL) >> > len = strlen(tkn); >> > @@ -186,10 +186,18 @@ decode_key_description(const char *desc, struct decoded_args *arg) >> > arg->hostname = SMB_XMALLOC_ARRAY(char, len); >> > strlcpy(arg->hostname, tkn + 5, len); >> > retval |= DKD_HAVE_HOSTNAME; >> > - } else if (strncmp(tkn, "ipv4=", 5) == 0) { >> > - /* BB: do we need it if we have hostname already? */ >> > - } else if (strncmp(tkn, "ipv6=", 5) == 0) { >> > - /* BB: do we need it if we have hostname already? */ >> > + } else if (!strncmp(tkn, "ip4=", 4) || >> > + !strncmp(tkn, "ip6=", 4)) { >> > + if (pos == NULL) >> > + len = strlen(tkn); >> > + else >> > + len = pos - tkn; >> > + >> > + len -= 3; >> > + SAFE_FREE(arg->ip); >> > + arg->ip = SMB_XMALLOC_ARRAY(char, len); >> > + strlcpy(arg->ip, tkn + 4, len); >> > + retval |= DKD_HAVE_IP; >> > } else if (strncmp(tkn, "pid=", 4) == 0) { >> > errno = 0; >> > arg->pid = strtol(tkn + 4, NULL, 0); >> > @@ -288,6 +296,35 @@ cifs_resolver(const key_serial_t key, const char *key_descr) >> > return 0; >> > } >> > >> > +static int >> > +ip_to_fqdn(const char *ipaddr, char *host, size_t hostlen) >> > +{ >> > + int rc; >> > + struct addrinfo hints = { .ai_flags = AI_NUMERICHOST }; >> > + struct addrinfo *res; >> > + >> > + rc = getaddrinfo(ipaddr, NULL, &hints, &res); >> > + if (rc) { >> > + syslog(LOG_DEBUG, "%s: failed to resolve %s to ipaddr: %s", >> > + __func__, ipaddr, >> > + rc == EAI_SYSTEM ? strerror(errno) : gai_strerror(rc)); >> > + return rc; >> > + } >> > + >> > + rc = getnameinfo(res->ai_addr, res->ai_addrlen, host, hostlen, >> > + NULL, 0, NI_NAMEREQD); >> > + freeaddrinfo(res); >> > + if (rc) { >> > + syslog(LOG_DEBUG, "%s: failed to resolve %s to fqdn: %s", >> > + __func__, ipaddr, >> > + rc == EAI_SYSTEM ? strerror(errno) : gai_strerror(rc)); >> > + return rc; >> > + } >> > + >> > + syslog(LOG_DEBUG, "%s: resolved %s to %s", __func__, ipaddr, host); >> > + return 0; >> > +} >> > + >> > static void >> > usage(void) >> > { >> > @@ -306,6 +343,7 @@ int main(const int argc, char *const argv[]) >> > long rc = 1; >> > int c; >> > char *buf, *princ, *ccname = NULL; >> > + char hostbuf[NI_MAXHOST]; >> > struct decoded_args arg = { }; >> > const char *oid; >> > >> > @@ -383,12 +421,18 @@ int main(const int argc, char *const argv[]) >> > } >> > } >> > >> > + if (have & DKD_HAVE_IP) { >> > + rc = ip_to_fqdn(arg.ip, hostbuf, sizeof(hostbuf)); >> > + if (rc) >> > + goto out; >> > + } >> > + >> > // do mech specific authorization >> > switch (arg.sec) { >> > case MS_KRB5: >> > case KRB5: >> > /* for "cifs/" service name + terminating 0 */ >> > - datalen = strlen(arg.hostname) + 5 + 1; >> > + datalen = strnlen(hostbuf, sizeof(hostbuf)) + 5 + 1; >> > princ = SMB_XMALLOC_ARRAY(char, datalen); >> > if (!princ) { >> > rc = 1; >> > @@ -405,7 +449,7 @@ int main(const int argc, char *const argv[]) >> > * getting a host/ principal if that doesn't work. >> > */ >> > strlcpy(princ, "cifs/", datalen); >> > - strlcpy(princ + 5, arg.hostname, datalen - 5); >> > + strlcpy(princ + 5, hostbuf, datalen - 5); >> > rc = handle_krb5_mech(oid, princ, &secblob, &sess_key, ccname); >> > if (rc) { >> > memcpy(princ, "host/", 5); >> > -- >> > 1.6.0.6 >> > >> > _______________________________________________ >> > linux-cifs-client mailing list >> > linux-cifs-client@lists.samba.org >> > https://lists.samba.org/mailman/listinfo/linux-cifs-client >> > > > > -- > Jeff Layton <jlayton@redhat.com> >
On Sun, 16 Aug 2009 23:52:46 +0400 "Q (Igor Mammedov)" <qwerty0987654321@mail.ru> wrote: > > I'll try explain more clearly, what I've meant. > > Providing that we could have compromised dns resolving, we could not > trust forward nor reverse resolution, but the goal of attacker is in > redirecting us his server. > Case 1: using host name A.B.C supplied at mount time > 1.1 we have an IP of a fake server because forward resolution was spoofed > 1.2 we get a valid session key from KDC for A.B.C > Result: we can detect that packets a coming from a fake server, because > of an incorrect signature. > > Case 2: using host name F.A.K.E from revers resolution > 2.1 the same attack vector 1.1, i.e. connect to a fake server's > IP, and doing > revers resolution we are getting host name of a fake server. > 2.2 we get a valid session key from KDC for F.A.K.E because of fake server > is a member of our domain. > Result: attacker forced us to use his server, nobody will even notice it. > > I prefer using 'case 1' for my files. And if cifs is fixed to drop a session > to a fake server, I will like it even more. > > Case 2 are safe only in a hardened network environment or with a secure > dns setup. > Ok, that makes sense. The attack vector is a little contrived, but I'm ok with preventing it. Still though, the fact that you need prior knowledge of what the host portion of the service principal should be is terribly problematic. Perhaps we should consider a "--trust-dns" flag or something that allows people to enable using reverse resolves? Any thoughts on other ways to prevent the problem where the hostname needed isn't known? > > There's a huge problem with the current scheme however. You need to > > know the canonical name of the host in the service ticket and then > > mount that. This is a huge source of confusion for users. Suppose I > > have a host: > > > > server.example.com > > > > ...and I have a principal that I need to get in order to mount it: > > > > cifs/server.example.com@EXAMPLE.COM > > > > ...now, suppose I try to mount up a share from that host, but use a > > non-canonical hostname in the server section of the UNC: > > > > //server/share > > > > ...it doesn't work. The upcall will try to assemble a principal name > > like: > > > > cifs/server@EXAMPLE.COM > > I haven't noticed this case because in AD domain, a machine > account is registered with a fqdn and a hostname principals. > (At least it is so in my company) > So I were able to connect to //server/share > > > ...similar problem if I try to mount a CNAME for the server. This is > > also a problem when you want to mix krb5 and DFS. I don't believe the > > current code sets the hostname. > > The same thing, I someone wishes to provide access to a server via > CNAMEs, he/she should create corresponding principals on KDC. > This way it will not reduce security. > The problem here is that it's not necessarily evident *why* the mount is failing at this point. If there were a way to spew a printk or log message that makes this evident then I'd be more conducive to it. > > > > I don't think so. The patch below also changes: > > > > #define DKD_MUSTHAVE_SET (DKD_HAVE_IP|DKD_HAVE_VERSION|DKD_HAVE_SEC) > > > > ...or am I missing something? > > It just caught my eyes. > Anyway I would initialized it, just in case. > Yeah, defensive coding doesn't hurt. I'll plan to initialize that once we come to consensus on what to do about the other problem.
diff --git a/client/cifs.upcall.c b/client/cifs.upcall.c index 38be876..1e58503 100644 --- a/client/cifs.upcall.c +++ b/client/cifs.upcall.c @@ -150,15 +150,15 @@ handle_krb5_mech(const char *oid, const char *principal, DATA_BLOB *secblob, #define DKD_HAVE_HOSTNAME 0x1 #define DKD_HAVE_VERSION 0x2 #define DKD_HAVE_SEC 0x4 -#define DKD_HAVE_IPV4 0x8 -#define DKD_HAVE_IPV6 0x10 -#define DKD_HAVE_UID 0x20 -#define DKD_HAVE_PID 0x40 -#define DKD_MUSTHAVE_SET (DKD_HAVE_HOSTNAME|DKD_HAVE_VERSION|DKD_HAVE_SEC) +#define DKD_HAVE_IP 0x8 +#define DKD_HAVE_UID 0x10 +#define DKD_HAVE_PID 0x20 +#define DKD_MUSTHAVE_SET (DKD_HAVE_IP|DKD_HAVE_VERSION|DKD_HAVE_SEC) static struct decoded_args { int ver; char *hostname; + char *ip; uid_t uid; pid_t pid; sectype_t sec; @@ -167,6 +167,7 @@ static struct decoded_args { static unsigned int decode_key_description(const char *desc, struct decoded_args *arg) { + int len; int retval = 0; char *pos; const char *tkn = desc; @@ -174,7 +175,6 @@ decode_key_description(const char *desc, struct decoded_args *arg) do { pos = index(tkn, ';'); if (strncmp(tkn, "host=", 5) == 0) { - int len; if (pos == NULL) len = strlen(tkn); @@ -186,10 +186,18 @@ decode_key_description(const char *desc, struct decoded_args *arg) arg->hostname = SMB_XMALLOC_ARRAY(char, len); strlcpy(arg->hostname, tkn + 5, len); retval |= DKD_HAVE_HOSTNAME; - } else if (strncmp(tkn, "ipv4=", 5) == 0) { - /* BB: do we need it if we have hostname already? */ - } else if (strncmp(tkn, "ipv6=", 5) == 0) { - /* BB: do we need it if we have hostname already? */ + } else if (!strncmp(tkn, "ip4=", 4) || + !strncmp(tkn, "ip6=", 4)) { + if (pos == NULL) + len = strlen(tkn); + else + len = pos - tkn; + + len -= 3; + SAFE_FREE(arg->ip); + arg->ip = SMB_XMALLOC_ARRAY(char, len); + strlcpy(arg->ip, tkn + 4, len); + retval |= DKD_HAVE_IP; } else if (strncmp(tkn, "pid=", 4) == 0) { errno = 0; arg->pid = strtol(tkn + 4, NULL, 0); @@ -288,6 +296,35 @@ cifs_resolver(const key_serial_t key, const char *key_descr) return 0; } +static int +ip_to_fqdn(const char *ipaddr, char *host, size_t hostlen) +{ + int rc; + struct addrinfo hints = { .ai_flags = AI_NUMERICHOST }; + struct addrinfo *res; + + rc = getaddrinfo(ipaddr, NULL, &hints, &res); + if (rc) { + syslog(LOG_DEBUG, "%s: failed to resolve %s to ipaddr: %s", + __func__, ipaddr, + rc == EAI_SYSTEM ? strerror(errno) : gai_strerror(rc)); + return rc; + } + + rc = getnameinfo(res->ai_addr, res->ai_addrlen, host, hostlen, + NULL, 0, NI_NAMEREQD); + freeaddrinfo(res); + if (rc) { + syslog(LOG_DEBUG, "%s: failed to resolve %s to fqdn: %s", + __func__, ipaddr, + rc == EAI_SYSTEM ? strerror(errno) : gai_strerror(rc)); + return rc; + } + + syslog(LOG_DEBUG, "%s: resolved %s to %s", __func__, ipaddr, host); + return 0; +} + static void usage(void) { @@ -306,6 +343,7 @@ int main(const int argc, char *const argv[]) long rc = 1; int c; char *buf, *princ, *ccname = NULL; + char hostbuf[NI_MAXHOST]; struct decoded_args arg = { }; const char *oid; @@ -383,12 +421,18 @@ int main(const int argc, char *const argv[]) } } + if (have & DKD_HAVE_IP) { + rc = ip_to_fqdn(arg.ip, hostbuf, sizeof(hostbuf)); + if (rc) + goto out; + } + // do mech specific authorization switch (arg.sec) { case MS_KRB5: case KRB5: /* for "cifs/" service name + terminating 0 */ - datalen = strlen(arg.hostname) + 5 + 1; + datalen = strnlen(hostbuf, sizeof(hostbuf)) + 5 + 1; princ = SMB_XMALLOC_ARRAY(char, datalen); if (!princ) { rc = 1; @@ -405,7 +449,7 @@ int main(const int argc, char *const argv[]) * getting a host/ principal if that doesn't work. */ strlcpy(princ, "cifs/", datalen); - strlcpy(princ + 5, arg.hostname, datalen - 5); + strlcpy(princ + 5, hostbuf, datalen - 5); rc = handle_krb5_mech(oid, princ, &secblob, &sess_key, ccname); if (rc) { memcpy(princ, "host/", 5);
Instead of using the hostname given by the upcall to get the server's principal, take the IP address given in the upcall and reverse resolve it to a hostname. Signed-off-by: Jeff Layton <jlayton@redhat.com> --- client/cifs.upcall.c | 68 +++++++++++++++++++++++++++++++++++++++++--------- 1 files changed, 56 insertions(+), 12 deletions(-)