[Bug libc/10818] New: printf("%s\n", NULL) segfaults

["kir at sacred dot ru" <sourceware-bugzilla at sourceware dot org>]

[kir@kir ~]$ cat null.c 
#include <stdio.h>

int main(void) {
	fprintf(stdout, "%s\n", NULL);
	printf("%s%s\n", NULL, NULL);
	printf("%s", NULL);
	printf("\n-newline-\n");
	printf("%s\n", NULL);
	return 0;
}
[kir@kir ~]$ gcc null.c
[kir@kir ~]$ ./a.out 
(null)
(null)(null)
(null)
-newline-
Segmentation fault

Note that only printf with "%s\n" segfaults, while others are fine.

This is because 
(1) call to printf("%s\n", str) is optimized to puts(str)
(2) puts(str) calls strlen(str)
(3) strlen(NULL) segfaults

System info:

$ rpm -q fedora-release gcc glibc
fedora-release-10-1.noarch
gcc-4.3.2-7.x86_64
glibc-2.9-3.i686
glibc-2.9-3.x86_64

PS
I discovered this bug when trying to do something like this:

	/* This should return NULL -- buflen is not big enough */
	printf("%s\n", inet_ntop(AF_INET, &in, buf, 2);

and got SIGSEGV instead of (null) being printed.

-- 
           Summary: printf("%s\n", NULL) segfaults
           Product: glibc
           Version: 2.9
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper at redhat dot com
        ReportedBy: kir at sacred dot ru
                CC: glibc-bugs at sources dot redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=10818

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