Re: [PATCH] Linux: Adjust gedents64 buffer size to int range [BZ #24740]

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 27/06/2019 06:39, Florian Weimer wrote:
> The kernel interface uses type unsigned int, but there is an
> internal conversion to int, so INT_MAX is the correct limit.
> Part of the buffer will always be unused, but this is not a
> problem.  Such huge buffers do not occur in practice anyway.
> 
> 2019-06-27  Florian Weimer  <fweimer@redhat.com>
> 
> 	[BZ #24740]
> 	* sysdeps/unix/sysv/linux/getdents64.c (__getdents64): Adjust
> 	buffer size if necessary.
> 	* sysdeps/unix/sysv/linux/mips/mips64/getdents64.c (__getdents64):
> 	Likewise.
> 	* sysdeps/unix/sysv/linux/tst-getdents64.c (large_buffer_check):
> 	New function.
> 	(large_buffer_checks): Likewise.
> 	(do_test): Call large_buffer_checks.

LGTM, maybe with a suggestion below for the tests.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

> 
> diff --git a/sysdeps/unix/sysv/linux/getdents64.c b/sysdeps/unix/sysv/linux/getdents64.c
> index a6dd22106d..5e3ef9994e 100644
> --- a/sysdeps/unix/sysv/linux/getdents64.c
> +++ b/sysdeps/unix/sysv/linux/getdents64.c
> @@ -19,11 +19,16 @@
>  #include <string.h>
>  #include <dirent.h>
>  #include <errno.h>
> +#include <limits.h>
>  
>  /* The kernel struct linux_dirent64 matches the 'struct dirent64' type.  */
>  ssize_t
>  __getdents64 (int fd, void *buf, size_t nbytes)
>  {
> +  /* The system call takes an unsigned int argument, and some length
> +     checks in the kernel use an int type.  */
> +  if (nbytes > INT_MAX)
> +    nbytes = INT_MAX;
>    return INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
>  }
>  libc_hidden_def (__getdents64)

Ok.

> diff --git a/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c b/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
> index 1e22fa4325..8bf3abb0e0 100644
> --- a/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
> +++ b/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
> @@ -23,12 +23,18 @@
>  #include <sys/param.h>
>  #include <unistd.h>
>  #include <scratch_buffer.h>
> +#include <limits.h>
>  
>  ssize_t
>  __getdents64 (int fd, void *buf0, size_t nbytes)
>  {
>    char *buf = buf0;
>  
> +  /* The system call takes an unsigned int argument, and some length
> +     checks in the kernel use an int type.  */
> +  if (nbytes > INT_MAX)
> +    nbytes = INT_MAX;
> +
>  #ifdef __NR_getdents64
>    ssize_t ret = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
>    if (ret != -1)

Ok.

> diff --git a/sysdeps/unix/sysv/linux/tst-getdents64.c b/sysdeps/unix/sysv/linux/tst-getdents64.c
> index c1f7721221..ece46123f3 100644
> --- a/sysdeps/unix/sysv/linux/tst-getdents64.c
> +++ b/sysdeps/unix/sysv/linux/tst-getdents64.c
> @@ -19,6 +19,7 @@
>  #include <dirent.h>
>  #include <errno.h>
>  #include <fcntl.h>
> +#include <limits.h>
>  #include <stdbool.h>
>  #include <stdio.h>
>  #include <stdlib.h>
> @@ -28,6 +29,48 @@
>  #include <support/xunistd.h>
>  #include <unistd.h>
>  
> +/* Called by large_buffer_checks below.  */
> +static void
> +large_buffer_check (int fd, char *large_buffer, size_t large_buffer_size)
> +{
> +  xlseek (fd, 0, SEEK_SET);
> +  ssize_t ret = getdents64 (fd, large_buffer, large_buffer_size);
> +  if (ret < 0)
> +    FAIL_EXIT1 ("getdents64 for buffer of %zu bytes failed: %m",
> +                large_buffer_size);
> +  if (ret < offsetof (struct dirent64, d_name))
> +    FAIL_EXIT1 ("getdents64 for buffer of %zu returned small value %zd",
> +                large_buffer_size, ret);
> +}
> +
> +/* Bug 24740: Make sure that the system call argument is adjusted
> +   properly for the int type.  A large value should stay a large
> +   value, and not wrap around to something small, causing the system
> +   call to fail with EINVAL.  */
> +static void
> +large_buffer_checks (int fd)
> +{
> +  size_t large_buffer_size = UINT_MAX;
> +  large_buffer_size += 2;
> +  if (large_buffer_size > 2)
> +    {

Maybe

  size_t large_buffer_size;
  if (!__builtin_add_overflow (UINT_MAX, 2, &large_buffer_size))
    { 

Instead?

> +      char *large_buffer = malloc (large_buffer_size);
> +      if (large_buffer == NULL)
> +        printf ("warning: could not allocate %zu bytes of memory,"
> +                " subtests skipped\n", large_buffer_size);
> +      else
> +        {
> +          large_buffer_check (fd, large_buffer, INT_MAX);
> +          large_buffer_check (fd, large_buffer, (size_t) INT_MAX + 1);
> +          large_buffer_check (fd, large_buffer, (size_t) INT_MAX + 2);
> +          large_buffer_check (fd, large_buffer, UINT_MAX);
> +          large_buffer_check (fd, large_buffer, (size_t) UINT_MAX + 1);
> +          large_buffer_check (fd, large_buffer, (size_t) UINT_MAX + 2);
> +        }
> +      free (large_buffer);
> +    }
> +}
> +
>  static int
>  do_test (void)
>  {
> @@ -105,6 +148,8 @@ do_test (void)
>        rewinddir (reference);
>      }
>  
> +  large_buffer_checks (fd);
> +
>    xclose (fd);
>    closedir (reference);
>    return 0;
> 

Ok.