File 0019-mountd-fix-segfault-in-add_name-with-newer-gcc-compi.patch of Package nfs-utils.12300

Commit: 25e83c2270b2d2966c992885faed0b79be09f474
References: bsc#937039
From: Jeff Layton <>
Date: Thu, 1 May 2014 11:15:16 -0400
Subject: [PATCH] mountd: fix segfault in add_name with newer gcc compilers

I hit a segfault in add_name with a mountd built with gcc-4.9.0. Some
NULL pointer checks got reordered such that a pointer was dereferenced
before checking to see whether it was NULL. The problem was due to
nfs-utils relying on undefined behavior, which tricked gcc into assuming
that the pointer would never be NULL.

At first I assumed that this was a compiler bug, but Jakub Jelinek and
Jeff Law pointed out:

"If old is NULL, then:

	strncpy(new, old, cp-old);

is undefined behavior (even when cp == old == NULL in that case),
therefore gcc assumes that old is never NULL, as otherwise it would be

Just guard
	strncpy(new, old, cp-old);
	new[cp-old] = 0;
with if (old) { ... }."

This patch does that. If old is NULL though, then we still need to
ensure that new is NULL terminated, lest the subsequent strcats walk off
the end of it.

Cc: Jeff Law <>
Cc: Jakub Jelinek <>
Signed-off-by: Jeff Layton <>
Signed-off-by: Steve Dickson <>
Acked-by: NeilBrown <>
 neilb: this may not be needed for SLE12, depending on the compiler
 used, but having it is better than not.
 support/export/client.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/support/export/client.c
+++ b/support/export/client.c
@@ -482,8 +482,12 @@ add_name(char *old, const char *add)
 			cp = cp + strlen(cp);
-	strncpy(new, old, cp-old);
-	new[cp-old] = 0;
+	if (old) {
+		strncpy(new, old, cp-old);
+		new[cp-old] = 0;
+	} else {
+		new[0] = 0;
+	}
 	if (cp != old && !*cp)
 		strcat(new, ",");
 	strcat(new, add);
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