| Message ID | 20210916084045.31684-3-hreitz@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | virtiofsd: Allow using file handles instead of O_PATH FDs | expand |
On Thu, Sep 16, 2021 at 10:40:35AM +0200, Hanna Reitz wrote: > We only need to drop/switch our credentials for the (f)setxattr() call > alone, not for the openat() or fchdir() around it. > > (Right now, this may not be that big of a problem, but with inodes being > identified by file handles instead of an O_PATH fd, we will need > open_by_handle_at() calls here, which is really fickle when it comes to > credentials being dropped.) > > Signed-off-by: Hanna Reitz <hreitz@redhat.com> > --- > tools/virtiofsd/passthrough_ll.c | 34 +++++++++++++++++++++++--------- > 1 file changed, 25 insertions(+), 9 deletions(-) > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > index 6511a6acb4..b43afdfbd3 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -3123,6 +3123,7 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, > bool switched_creds = false; > bool cap_fsetid_dropped = false; > struct lo_cred old = {}; > + bool changed_cwd = false; > > if (block_xattr(lo, in_name)) { > fuse_reply_err(req, EOPNOTSUPP); > @@ -3158,6 +3159,24 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, > ", name=%s value=%s size=%zd)\n", ino, name, value, size); > > sprintf(procname, "%i", inode->fd); > + /* > + * We can only open regular files or directories. If the inode is > + * something else, we have to enter /proc/self/fd and use > + * setxattr() on the link's filename there. > + */ > + if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) { > + fd = openat(lo->proc_self_fd, procname, O_RDONLY); > + if (fd < 0) { > + saverr = errno; > + goto out; > + } > + } else { > + /* fchdir should not fail here */ > + FCHDIR_NOFAIL(lo->proc_self_fd); > + /* Set flag so the clean-up path will chdir back */ > + changed_cwd = true; Is there a need to move FCHDIR_NOFAIL() call earlier too? I am assuming this will not be impacted by file handle stuff. So we probably could leave it in place. Easier to read. Vivek > + } > + > /* > * If we are setting posix access acl and if SGID needs to be > * cleared, then switch to caller's gid and drop CAP_FSETID > @@ -3178,20 +3197,12 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, > } > switched_creds = true; > } > - if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) { > - fd = openat(lo->proc_self_fd, procname, O_RDONLY); > - if (fd < 0) { > - saverr = errno; > - goto out; > - } > + if (fd >= 0) { > ret = fsetxattr(fd, name, value, size, flags); > saverr = ret == -1 ? errno : 0; > } else { > - /* fchdir should not fail here */ > - FCHDIR_NOFAIL(lo->proc_self_fd); > ret = setxattr(procname, name, value, size, flags); > saverr = ret == -1 ? errno : 0; > - FCHDIR_NOFAIL(lo->root.fd); > } > if (switched_creds) { > if (cap_fsetid_dropped) > @@ -3201,6 +3212,11 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, > } > > out: > + if (changed_cwd) { > + /* Change CWD back, fchdir should not fail here */ > + FCHDIR_NOFAIL(lo->root.fd); > + } > + > if (fd >= 0) { > close(fd); > } > -- > 2.31.1 >
On 18.10.21 19:20, Vivek Goyal wrote: > On Thu, Sep 16, 2021 at 10:40:35AM +0200, Hanna Reitz wrote: >> We only need to drop/switch our credentials for the (f)setxattr() call >> alone, not for the openat() or fchdir() around it. >> >> (Right now, this may not be that big of a problem, but with inodes being >> identified by file handles instead of an O_PATH fd, we will need >> open_by_handle_at() calls here, which is really fickle when it comes to >> credentials being dropped.) >> >> Signed-off-by: Hanna Reitz <hreitz@redhat.com> >> --- >> tools/virtiofsd/passthrough_ll.c | 34 +++++++++++++++++++++++--------- >> 1 file changed, 25 insertions(+), 9 deletions(-) >> >> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c >> index 6511a6acb4..b43afdfbd3 100644 >> --- a/tools/virtiofsd/passthrough_ll.c >> +++ b/tools/virtiofsd/passthrough_ll.c >> @@ -3123,6 +3123,7 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, >> bool switched_creds = false; >> bool cap_fsetid_dropped = false; >> struct lo_cred old = {}; >> + bool changed_cwd = false; >> >> if (block_xattr(lo, in_name)) { >> fuse_reply_err(req, EOPNOTSUPP); >> @@ -3158,6 +3159,24 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, >> ", name=%s value=%s size=%zd)\n", ino, name, value, size); >> >> sprintf(procname, "%i", inode->fd); >> + /* >> + * We can only open regular files or directories. If the inode is >> + * something else, we have to enter /proc/self/fd and use >> + * setxattr() on the link's filename there. >> + */ >> + if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) { >> + fd = openat(lo->proc_self_fd, procname, O_RDONLY); >> + if (fd < 0) { >> + saverr = errno; >> + goto out; >> + } >> + } else { >> + /* fchdir should not fail here */ >> + FCHDIR_NOFAIL(lo->proc_self_fd); >> + /* Set flag so the clean-up path will chdir back */ >> + changed_cwd = true; > Is there a need to move FCHDIR_NOFAIL() call earlier too? I am assuming > this will not be impacted by file handle stuff. So we probably could > leave it in place. Easier to read. I wanted to limit the region where the creds are dropped to an absolute minimum, i.e. just around (f)setxattr(). I prefer this in general, not just because it breaks opening file handles, and so I wanted to pull out not just the openat(), but the fchdir() as well. Hanna
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 6511a6acb4..b43afdfbd3 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -3123,6 +3123,7 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, bool switched_creds = false; bool cap_fsetid_dropped = false; struct lo_cred old = {}; + bool changed_cwd = false; if (block_xattr(lo, in_name)) { fuse_reply_err(req, EOPNOTSUPP); @@ -3158,6 +3159,24 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, ", name=%s value=%s size=%zd)\n", ino, name, value, size); sprintf(procname, "%i", inode->fd); + /* + * We can only open regular files or directories. If the inode is + * something else, we have to enter /proc/self/fd and use + * setxattr() on the link's filename there. + */ + if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) { + fd = openat(lo->proc_self_fd, procname, O_RDONLY); + if (fd < 0) { + saverr = errno; + goto out; + } + } else { + /* fchdir should not fail here */ + FCHDIR_NOFAIL(lo->proc_self_fd); + /* Set flag so the clean-up path will chdir back */ + changed_cwd = true; + } + /* * If we are setting posix access acl and if SGID needs to be * cleared, then switch to caller's gid and drop CAP_FSETID @@ -3178,20 +3197,12 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, } switched_creds = true; } - if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) { - fd = openat(lo->proc_self_fd, procname, O_RDONLY); - if (fd < 0) { - saverr = errno; - goto out; - } + if (fd >= 0) { ret = fsetxattr(fd, name, value, size, flags); saverr = ret == -1 ? errno : 0; } else { - /* fchdir should not fail here */ - FCHDIR_NOFAIL(lo->proc_self_fd); ret = setxattr(procname, name, value, size, flags); saverr = ret == -1 ? errno : 0; - FCHDIR_NOFAIL(lo->root.fd); } if (switched_creds) { if (cap_fsetid_dropped) @@ -3201,6 +3212,11 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, } out: + if (changed_cwd) { + /* Change CWD back, fchdir should not fail here */ + FCHDIR_NOFAIL(lo->root.fd); + } + if (fd >= 0) { close(fd); }
We only need to drop/switch our credentials for the (f)setxattr() call alone, not for the openat() or fchdir() around it. (Right now, this may not be that big of a problem, but with inodes being identified by file handles instead of an O_PATH fd, we will need open_by_handle_at() calls here, which is really fickle when it comes to credentials being dropped.) Signed-off-by: Hanna Reitz <hreitz@redhat.com> --- tools/virtiofsd/passthrough_ll.c | 34 +++++++++++++++++++++++--------- 1 file changed, 25 insertions(+), 9 deletions(-)