[glibc/release/2.39/master] parse_fdinfo: Don't advance pointer twice [BZ #31798]

[glibc/release/2.39/master] parse_fdinfo: Don't advance pointer twice [BZ #31798]

[H.J. Lu]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9f2b100d6705b9bbb25206b53e80d7759644e06e

commit 9f2b100d6705b9bbb25206b53e80d7759644e06e
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Sat May 25 05:13:41 2024 -0700

    parse_fdinfo: Don't advance pointer twice [BZ #31798]
    
    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>
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
    (cherry picked from commit f981bf6b9db87e0732b46bfe92fdad4d363225e8)

Diff:
---
 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 8567b413dd..30025e5863 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.  */