[v4] nss: reject invalid port passed to getaddrinfo [BZ #16208]

When passing a numeric string as port/service to getaddrinfo()
representing a number larger than 65535, the function will not
complain and will simply extract the lowest 16bits of the
converted number.

Specifically, the string is converted to int by calling strtoul()
and later it is moved to gaih_servtuple.num after passing through
htons().

For example, invoking getaddrinfo() with service equal to "70000"
will result in no error and ai_addr->sin_port set to 4464.

This issue was (re)discovered by researcher Anqi Chen while stress
testing OpenVPN with invalid config parameters.

Thanks a lot to Arne Schwabe for finding out that the root
cause was hidden inside glibc.

Similarly when passing an out of range value, no error
is thrown while it should.

Add proper checks to reject invalid values immediately.

The 'num' member has been converted to unsigned long in order
to properly store the result of strtoul(). Then, while checking for
'num' being greater than USHRT_MAX, we also catch overflows/out-of-range
values (strtoul() returns ULONG_MAX in that case).

Cc: Arne Schwabe <arne@rfc2549.org>
Cc: Cristina Nita-Rotaru <crisn@ccs.neu.edu>
Reported-by: Anqi Chen <chen.anqi3@northeastern.edu>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

---
Changes from v4:
* used USHRT_MAX + 1 to report parsing error
* added unit test for port parsing error ("10haha")

Changes from v3:
* extended unit test with more notorius integer constants
* rephrased comment
* removed mention of 0 being invalid from commit message

Changes from v2:
* allowed specifying 0 as port number (equivalent to not passing any
  port)
* changed unit-test to check success when passing 0 as port
---
 nss/Makefile           |  1 +
 nss/getaddrinfo.c      | 17 +++++++--
 nss/tst-getaddrinfo6.c | 85 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 100 insertions(+), 3 deletions(-)
 create mode 100644 nss/tst-getaddrinfo6.c

Subject was supposed to say "PATCH v5" - sorry for the mistake.

On 30/10/2024 01:07, Antonio Quartulli wrote:
> When passing a numeric string as port/service to getaddrinfo()
> representing a number larger than 65535, the function will not
> complain and will simply extract the lowest 16bits of the
> converted number.
> 
> Specifically, the string is converted to int by calling strtoul()
> and later it is moved to gaih_servtuple.num after passing through
> htons().
> 
> For example, invoking getaddrinfo() with service equal to "70000"
> will result in no error and ai_addr->sin_port set to 4464.
> 
> This issue was (re)discovered by researcher Anqi Chen while stress
> testing OpenVPN with invalid config parameters.
> 
> Thanks a lot to Arne Schwabe for finding out that the root
> cause was hidden inside glibc.
> 
> Similarly when passing an out of range value, no error
> is thrown while it should.
> 
> Add proper checks to reject invalid values immediately.
> 
> The 'num' member has been converted to unsigned long in order
> to properly store the result of strtoul(). Then, while checking for
> 'num' being greater than USHRT_MAX, we also catch overflows/out-of-range
> values (strtoul() returns ULONG_MAX in that case).
> 
> Cc: Arne Schwabe <arne@rfc2549.org>
> Cc: Cristina Nita-Rotaru <crisn@ccs.neu.edu>
> Reported-by: Anqi Chen <chen.anqi3@northeastern.edu>
> Signed-off-by: Antonio Quartulli <a@unstable.cc>
> 
> ---
> Changes from v4:
> * used USHRT_MAX + 1 to report parsing error
> * added unit test for port parsing error ("10haha")
> 
> Changes from v3:
> * extended unit test with more notorius integer constants
> * rephrased comment
> * removed mention of 0 being invalid from commit message
> 
> Changes from v2:
> * allowed specifying 0 as port number (equivalent to not passing any
>    port)
> * changed unit-test to check success when passing 0 as port
> ---
>   nss/Makefile           |  1 +
>   nss/getaddrinfo.c      | 17 +++++++--
>   nss/tst-getaddrinfo6.c | 85 ++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 100 insertions(+), 3 deletions(-)
>   create mode 100644 nss/tst-getaddrinfo6.c
> 
> diff --git a/nss/Makefile b/nss/Makefile
> index 9331b3308c..94acfd0e38 100644
> --- a/nss/Makefile
> +++ b/nss/Makefile
> @@ -321,6 +321,7 @@ tests := \
>     tst-getaddrinfo \
>     tst-getaddrinfo2 \
>     tst-getaddrinfo3 \
> +  tst-getaddrinfo6 \
>     tst-gethnm \
>     tst-getpw \
>     tst-gshadow \
> diff --git a/nss/getaddrinfo.c b/nss/getaddrinfo.c
> index 3ccd3905fa..0e5984ef1b 100644
> --- a/nss/getaddrinfo.c
> +++ b/nss/getaddrinfo.c
> @@ -95,7 +95,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>   struct gaih_service
>     {
>       const char *name;
> -    int num;
> +    unsigned long num;
>     };
>   
>   struct gaih_servtuple
> @@ -414,7 +414,7 @@ get_servtuples (const struct gaih_service *service, const struct addrinfo *req,
>     if (service != NULL && (tp->protoflag & GAI_PROTO_NOSERVICE) != 0)
>       return -EAI_SERVICE;
>   
> -  if (service == NULL || service->num >= 0)
> +  if (service == NULL || (service->num >= 0 && service->num <= USHRT_MAX))
>       {
>         int port = service != NULL ? htons (service->num) : 0;
>   
> @@ -2375,7 +2375,18 @@ getaddrinfo (const char *name, const char *service,
>   	      return EAI_NONAME;
>   	    }
>   
> -	  gaih_service.num = -1;
> +	  /* use an out-of-range value to report the parsing error */
> +	  gaih_service.num = USHRT_MAX + 1;
> +	}
> +      /* port number must be in range [0, USHRT_MAX].
> +         Any other value is invalid.
> +         strtoul returns ULONG_MAX in case of out-of-range
> +         input and it is caught by this check */
> +      else if (gaih_service.num > USHRT_MAX)
> +	{
> +	  /* the provided port number is invalid */
> +	  __free_in6ai (in6ai);
> +	  return EAI_NONAME;
>   	}
>   
>         pservice = &gaih_service;
> diff --git a/nss/tst-getaddrinfo6.c b/nss/tst-getaddrinfo6.c
> new file mode 100644
> index 0000000000..2ecd0f07e0
> --- /dev/null
> +++ b/nss/tst-getaddrinfo6.c
> @@ -0,0 +1,85 @@
> +/* Test invalid port/service lookup [BZ #16208].
> +   Copyright (C) 2014-2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <stdio.h>
> +#include <string.h>
> +#include <sys/types.h>
> +#include <sys/socket.h>
> +#include <netinet/in.h>
> +#include <netdb.h>
> +
> +static int
> +do_one_test (const char *service, int expected_err)
> +{
> +  const int family[2] = { AF_INET, AF_INET6 };
> +  struct addrinfo hints, *aitop;
> +  int index, gaierr;
> +  int result = 0;
> +
> +  for (index = 0; index < sizeof (family) / sizeof (family[0]); ++index)
> +    {
> +      memset (&hints, '\0', sizeof (hints));
> +      hints.ai_family = family[index];
> +
> +      gaierr = getaddrinfo (NULL, service, &hints, &aitop);
> +      if (gaierr != expected_err)
> +	{
> +	  printf ("FAIL getaddrinfo returned %d, should return %d\n",
> +		  gaierr, expected_err);
> +	  result = 1;
> +	}
> +    }
> +
> +  return result;
> +}
> +
> +
> +static int
> +do_test (void)
> +{
> +  int err = 0;
> +
> +  // 0 is accepted, test should succeed
> +  err |= do_one_test ("0", 0);
> +  err |= do_one_test ("70000", EAI_NONAME);
> +  err |= do_one_test ("-1", EAI_NONAME);
> +  err |= do_one_test ("10haha", EAI_SERVICE);
> +
> +  // INT_MIN
> +  err |= do_one_test ("-2147483648", EAI_NONAME);
> +  // INT_MAX
> +  err |= do_one_test ("2147483647", EAI_NONAME);
> +  // UINT_MAX / ULONG_MAX 32bit
> +  err |= do_one_test ("4294967295", EAI_NONAME);
> +  // ULONG_MAX 64bit / ULLONG_MAX
> +  err |= do_one_test ("18446744073709551615", EAI_NONAME);
> +  // LONG_MAX 64bit / LLONG_MAX
> +  err |= do_one_test ("9223372036854775807", EAI_NONAME);
> +  // LONG_MIN 64bit / LLONG_MIN
> +  err |= do_one_test ("-9223372036854775808", EAI_NONAME);
> +
> +  // ULONG_MAX 64bit +1 / ULLONG_MAX +1
> +  err |= do_one_test ("18446744073709551616", EAI_NONAME);
> +  // LONG_MIN 64bit -1 / LLONG_MIN -1
> +  err |= do_one_test ("-9223372036854775809", EAI_NONAME);
> +
> +  return err;
> +}
> +#define TEST_FUNCTION do_test ()
> +
> +#include "../test-skeleton.c"

Hi Antonio,

> @@ -414,7 +414,7 @@ get_servtuples (const struct gaih_service *service, const struct addrinfo *req,
>     if (service != NULL && (tp->protoflag & GAI_PROTO_NOSERVICE) != 0)
>       return -EAI_SERVICE;
>  
> -  if (service == NULL || service->num >= 0)
> +  if (service == NULL || (service->num >= 0 && service->num <= USHRT_MAX))

OK.

> @@ -2375,7 +2375,18 @@ getaddrinfo (const char *name, const char *service,
>              return EAI_NONAME;
>            }
>  
> -       gaih_service.num = -1;
> +       /* use an out-of-range value to report the parsing error */
> +       gaih_service.num = USHRT_MAX + 1;
> +     }
> +      /* port number must be in range [0, USHRT_MAX].
> +         Any other value is invalid.
> +         strtoul returns ULONG_MAX in case of out-of-range
> +         input and it is caught by this check */
> +      else if (gaih_service.num > USHRT_MAX)
> +     {
> +       /* the provided port number is invalid */
> +       __free_in6ai (in6ai);
> +       return EAI_NONAME;
>        }

So I'm still confused by this one - basically this treats "10000a" differently
from "100001". If the provided port number is a valid number but too large,
can we assume that AI_NUMERICSERV is set and return an error?

It may be better to treat it like an invalid port number, eg. something like:

      gaih_service.num = strtoul (gaih_service.name, &c, 10);
      /* port number must be a valid number with range [0, USHRT_MAX].
          strtoul returns ULONG_MAX in case of out-of-range.  */
      if (*c != '\0' || gaih_service.num > USHRT_MAX)
        {
          if (hints->ai_flags & AI_NUMERICSERV)
            {
              __free_in6ai (in6ai);
              return EAI_NONAME;
            }

          gaih_service.num = USHRT_MAX + 1;
        }

Cheers,
Wilco