parse_fdinfo: Don't advance pointer twice [BZ #31798]

Message ID 20240525121341.3154251-1-hjl.tools@gmail.com
State Committed
Commit f981bf6b9db87e0732b46bfe92fdad4d363225e8
Headers
Series parse_fdinfo: Don't advance pointer twice [BZ #31798] |

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Commit Message

H.J. Lu May 25, 2024, 12:13 p.m. UTC
  pidfd_getpid.c has

      /* Ignore invalid large values.  */
      if (INT_MULTIPLY_WRAPV (10, n, &n)
          || INT_ADD_WRAPV (n, *l++ - '0', &n))
        return -1;

For GCC older than GCC 7, INT_ADD_WRAPV(a, b, r) is defined as

   _GL_INT_OP_WRAPV (a, b, r, +, _GL_INT_ADD_RANGE_OVERFLOW)

and *l++ - '0' is evaluated twice.  Fix BZ #31798 by moving "l++" out of
the if statement.  Tested with GCC 6.4 and GCC 14.1.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
---
 sysdeps/unix/sysv/linux/pidfd_getpid.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
  

Comments

Adhemerval Zanella Netto May 27, 2024, 1:28 p.m. UTC | #1
On 25/05/24 09:13, H.J. Lu wrote:
> pidfd_getpid.c has
> 
>       /* Ignore invalid large values.  */
>       if (INT_MULTIPLY_WRAPV (10, n, &n)
>           || INT_ADD_WRAPV (n, *l++ - '0', &n))
>         return -1;
> 
> For GCC older than GCC 7, INT_ADD_WRAPV(a, b, r) is defined as
> 
>    _GL_INT_OP_WRAPV (a, b, r, +, _GL_INT_ADD_RANGE_OVERFLOW)
> 
> and *l++ - '0' is evaluated twice.  Fix BZ #31798 by moving "l++" out of
> the if statement.  Tested with GCC 6.4 and GCC 14.1.
> 
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>

The intprops.h is clear about it:

341    These macros may evaluate their arguments zero or multiple times, so the
342    arguments should not have side effects.

LGTM, thanks.

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


> ---
>  sysdeps/unix/sysv/linux/pidfd_getpid.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/pidfd_getpid.c b/sysdeps/unix/sysv/linux/pidfd_getpid.c
> index ebcbe8fdf6..6967477fab 100644
> --- a/sysdeps/unix/sysv/linux/pidfd_getpid.c
> +++ b/sysdeps/unix/sysv/linux/pidfd_getpid.c
> @@ -74,8 +74,10 @@ parse_fdinfo (const char *l, void *arg)
>  
>        /* Ignore invalid large values.  */
>        if (INT_MULTIPLY_WRAPV (10, n, &n)
> -          || INT_ADD_WRAPV (n, *l++ - '0', &n))
> +          || INT_ADD_WRAPV (n, *l - '0', &n))
>          return -1;
> +
> +      l++;
>      }
>  
>    /* -1 indicates that the process is terminated.  */
  

Patch

diff --git a/sysdeps/unix/sysv/linux/pidfd_getpid.c b/sysdeps/unix/sysv/linux/pidfd_getpid.c
index ebcbe8fdf6..6967477fab 100644
--- a/sysdeps/unix/sysv/linux/pidfd_getpid.c
+++ b/sysdeps/unix/sysv/linux/pidfd_getpid.c
@@ -74,8 +74,10 @@  parse_fdinfo (const char *l, void *arg)
 
       /* Ignore invalid large values.  */
       if (INT_MULTIPLY_WRAPV (10, n, &n)
-          || INT_ADD_WRAPV (n, *l++ - '0', &n))
+          || INT_ADD_WRAPV (n, *l - '0', &n))
         return -1;
+
+      l++;
     }
 
   /* -1 indicates that the process is terminated.  */