[05/13] resolv: Add internal __ns_name_length_uncompressed function

---
 include/arpa/nameser.h                   |   8 ++
 resolv/Makefile                          |   5 +
 resolv/ns_name_length_uncompressed.c     |  72 ++++++++++++
 resolv/tst-ns_name_length_uncompressed.c | 135 +++++++++++++++++++++++
 4 files changed, 220 insertions(+)
 create mode 100644 resolv/ns_name_length_uncompressed.c
 create mode 100644 resolv/tst-ns_name_length_uncompressed.c

On 2022-08-10 05:30, Florian Weimer via Libc-alpha wrote:
> ---
>   include/arpa/nameser.h                   |   8 ++
>   resolv/Makefile                          |   5 +
>   resolv/ns_name_length_uncompressed.c     |  72 ++++++++++++
>   resolv/tst-ns_name_length_uncompressed.c | 135 +++++++++++++++++++++++
>   4 files changed, 220 insertions(+)
>   create mode 100644 resolv/ns_name_length_uncompressed.c
>   create mode 100644 resolv/tst-ns_name_length_uncompressed.c

LGTM.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

> 
> diff --git a/include/arpa/nameser.h b/include/arpa/nameser.h
> index bb1dede187..6e4808f00d 100644
> --- a/include/arpa/nameser.h
> +++ b/include/arpa/nameser.h
> @@ -95,5 +95,13 @@ libc_hidden_proto (__ns_name_unpack)
>   extern __typeof (ns_samename) __libc_ns_samename;
>   libc_hidden_proto (__libc_ns_samename)
>   
> +/* Packet parser helper functions.  */
> +
> +/* Verify that P points to an uncompressed domain name in wire format.
> +   On success, return the length of the encoded name, including the
> +   terminating null byte.  On failure, return -1 and set errno.  EOM
> +   must point one past the last byte in the packet.  */
> +int __ns_name_length_uncompressed (const unsigned char *p,
> +				   const unsigned char *eom) attribute_hidden;
>   # endif /* !_ISOMAC */
>   #endif
> diff --git a/resolv/Makefile b/resolv/Makefile
> index ec61ad07bd..bf28825f60 100644
> --- a/resolv/Makefile
> +++ b/resolv/Makefile
> @@ -40,6 +40,7 @@ routines := \
>     inet_pton \
>     ns_makecanon \
>     ns_name_compress \
> +  ns_name_length_uncompressed \
>     ns_name_ntop \
>     ns_name_pack \
>     ns_name_pton \
> @@ -111,6 +112,10 @@ tests-static += tst-resolv-txnid-collision
>   tests-internal += tst-ns_samebinaryname
>   tests-static += tst-ns_samebinaryname
>   
> +# Likewise for __ns_name_length_uncompressed.
> +tests-internal += tst-ns_name_length_uncompressed
> +tests-static += tst-ns_name_length_uncompressed
> +
>   # These tests need libdl.
>   ifeq (yes,$(build-shared))
>   tests += \
> diff --git a/resolv/ns_name_length_uncompressed.c b/resolv/ns_name_length_uncompressed.c
> new file mode 100644
> index 0000000000..51296b47ef
> --- /dev/null
> +++ b/resolv/ns_name_length_uncompressed.c
> @@ -0,0 +1,72 @@
> +/* Skip over an uncompressed name in wire format.
> +   Copyright (C) 2022 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 <arpa/nameser.h>
> +#include <errno.h>
> +#include <stdbool.h>
> +
> +int
> +__ns_name_length_uncompressed (const unsigned char *p,
> +                                const unsigned char *eom)
> +{
> +  const unsigned char *start = p;
> +
> +  while (true)
> +    {
> +      if (p == eom)
> +        {
> +          /* Truncated packet: no room for label length.  */
> +          __set_errno (EMSGSIZE);
> +          return -1;
> +        }
> +
> +      unsigned char b = *p;
> +      ++p;
> +      if (b == 0)
> +        {
> +          /* Root label.  */
> +          size_t length = p - start;
> +          if (length > NS_MAXCDNAME)
> +            {
> +              /* Domain name too long.  */
> +              __set_errno (EMSGSIZE);
> +              return -1;
> +            }
> +          return length;
> +        }
> +
> +      if (b <= 63)
> +        {
> +          /* Regular label.  */
> +          if (b <= eom - p)
> +            p += b;
> +          else
> +            {
> +              /* Truncated packet: label incomplete.  */
> +              __set_errno (EMSGSIZE);
> +              return -1;
> +            }
> +        }
> +      else
> +        {
> +          /* Compression reference or corrupted label length.  */
> +          __set_errno (EMSGSIZE);
> +          return -1;
> +        }
> +    }
> +}
> diff --git a/resolv/tst-ns_name_length_uncompressed.c b/resolv/tst-ns_name_length_uncompressed.c
> new file mode 100644
> index 0000000000..c4a2904db7
> --- /dev/null
> +++ b/resolv/tst-ns_name_length_uncompressed.c
> @@ -0,0 +1,135 @@
> +/* Test __ns_name_length_uncompressed.
> +   Copyright (C) 2022 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 <arpa/nameser.h>
> +#include <array_length.h>
> +#include <errno.h>
> +#include <stdio.h>
> +#include <support/check.h>
> +#include <support/next_to_fault.h>
> +
> +/* Reference implementation based on other building blocks.  */
> +static int
> +reference_length (const unsigned char *p, const unsigned char *eom)
> +{
> +  unsigned char buf[NS_MAXCDNAME];
> +  int n = __ns_name_unpack (p, eom, p, buf, sizeof (buf));
> +  if (n < 0)
> +    return n;
> +  const unsigned char *q = buf;
> +  if (__ns_name_skip (&q, array_end (buf)) < 0)
> +    return -1;
> +  if (q - buf != n)
> +    /* Compressed name.  */
> +    return -1;
> +  return n;
> +}
> +
> +static int
> +do_test (void)
> +{
> +  {
> +    unsigned char buf[] = { 3, 'w', 'w', 'w', 0, 0, 0 };
> +    TEST_COMPARE (reference_length (buf, array_end (buf)), sizeof (buf) - 2);
> +    TEST_COMPARE (__ns_name_length_uncompressed (buf, array_end (buf)),
> +                  sizeof (buf) - 2);
> +    TEST_COMPARE (reference_length (array_end (buf) - 1, array_end (buf)), 1);
> +    TEST_COMPARE (__ns_name_length_uncompressed (array_end (buf) - 1,
> +                                                 array_end (buf)), 1);
> +    buf[4]  = 0xc0;             /* Forward compression reference.  */
> +    buf[5]  = 0x06;
> +    TEST_COMPARE (reference_length (buf, array_end (buf)), -1);
> +    TEST_COMPARE (__ns_name_length_uncompressed (buf, array_end (buf)), -1);
> +  }
> +
> +  struct support_next_to_fault ntf = support_next_to_fault_allocate (300);
> +
> +  /* Buffer region with all possible bytes at start and end.  */
> +  for (int length = 1; length <= 300; ++length)
> +    {
> +      unsigned char *end = (unsigned char *) ntf.buffer + ntf.length;
> +      unsigned char *start = end - length;
> +      memset (start, 'X', length);
> +      for (int first = 0; first <= 255; ++first)
> +        {
> +          *start = first;
> +          for (int last = 0; last <= 255; ++last)
> +            {
> +              start[length - 1] = last;
> +              TEST_COMPARE (reference_length (start, end),
> +                            __ns_name_length_uncompressed (start, end));
> +            }
> +        }
> +    }
> +
> +  /* Poor man's fuzz testing: patch two bytes.   */
> +  {
> +    unsigned char ref[] =
> +      {
> +        7, 'e', 'x', 'a', 'm', 'p', 'l', 'e', 3, 'n', 'e', 't', 0, 0, 0
> +      };
> +    TEST_COMPARE (reference_length (ref, array_end (ref)), 13);
> +    TEST_COMPARE (__ns_name_length_uncompressed (ref, array_end (ref)), 13);
> +
> +    int good = 0;
> +    int bad = 0;
> +    for (int length = 1; length <= sizeof (ref); ++length)
> +      {
> +        unsigned char *end = (unsigned char *) ntf.buffer + ntf.length;
> +        unsigned char *start = end - length;
> +        memcpy (start, ref, length);
> +
> +        for (int patch1_pos = 0; patch1_pos < length; ++patch1_pos)
> +          {
> +            for (int patch1_value = 0; patch1_value <= 255; ++patch1_value)
> +              {
> +                start[patch1_pos] = patch1_value;
> +                for (int patch2_pos = 0; patch2_pos < length; ++patch2_pos)
> +                  {
> +                    for (int patch2_value = 0; patch2_value <= 255;
> +                         ++patch2_value)
> +                      {
> +                        start[patch2_pos] = patch2_value;
> +                        int expected = reference_length (start, end);
> +                        errno = EINVAL;
> +                        int actual
> +                          =  __ns_name_length_uncompressed (start, end);
> +                        if (actual > 0)
> +                          ++good;
> +                        else
> +                          {
> +                            TEST_COMPARE (errno, EMSGSIZE);
> +                            ++bad;
> +                          }
> +                        TEST_COMPARE (expected, actual);
> +                      }
> +                    start[patch2_pos] = ref[patch2_pos];
> +                  }
> +              }
> +            start[patch1_pos] = ref[patch1_pos];
> +          }
> +      }
> +    printf ("info: patched inputs with success: %d\n", good);
> +    printf ("info: patched inputs with failure: %d\n", bad);
> +  }
> +
> +  support_next_to_fault_free (&ntf);
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>