Bug#794947: manpages-dev: printf(3) example: possible integer overflow

retitle 794947 printf(3): possible integer overflow in make_message example
severity 794947 wishlist
tags 794947 + confirmed
tags 794947 + upstream
forwarded 794947 linux-man@vger.kernel.org
stop

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Hello Walter,

Jakub Wilk reported a possible integer overflow in make_message example :

The example in the printf(3) manpages looks like this (with boring parts
omitted):

int n;
/* ... */
  n = vsnprintf(p, size, fmt, ap);
   /* ... */
   if (n < 0) {
       /* ... */
       return NULL;
   }
   /* ... */
   size = n + 1;


But vsnprintf could return INT_MAX, which would then cause "n + 1" to
overflow.

(AFAICS, the glibc vsnprintf implementation never returns INT_MAX, but
it could in principle.)

I'd suggest changing "n < 0" to "n < 0 || n == INT_MAX".

Since this example has been modified by you (Walter Harms), after the bug #794947 [1] has been reported, I wanted to ask your opinion on the best option.

Should we add this test to good practice, or rather a comment to mention that the case is not taken into account because the example uses glibc?

Regards,

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=794947

-- 
Stéphane Aulery