[PATCH 08/14] lib/kasprintf.c: add sanity check to kvasprintf

From: Rasmus Villemoes
Date: Mon Nov 23 2015 - 16:30:07 EST

kasprintf relies on being able to replay the formatting and getting
the same result (in particular, the same length). This will almost
always work, but it is possible that the object pointed to by a %s or
%p argument changed under us (so we might get truncated output). Add a
somewhat paranoid sanity check and let's see if it ever triggers.

Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
lib/kasprintf.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/kasprintf.c b/lib/kasprintf.c
index f194e6e593e1..7f6c506a4942 100644
--- a/lib/kasprintf.c
+++ b/lib/kasprintf.c
@@ -13,19 +13,21 @@
/* Simplified asprintf. */
char *kvasprintf(gfp_t gfp, const char *fmt, va_list ap)
- unsigned int len;
+ unsigned int first, second;
char *p;
va_list aq;

va_copy(aq, ap);
- len = vsnprintf(NULL, 0, fmt, aq);
+ first = vsnprintf(NULL, 0, fmt, aq);

- p = kmalloc_track_caller(len+1, gfp);
+ p = kmalloc_track_caller(first+1, gfp);
if (!p)
return NULL;

- vsnprintf(p, len+1, fmt, ap);
+ second = vsnprintf(p, first+1, fmt, ap);
+ WARN(first != second, "different return values (%u and %u) from vsnprintf(\"%s\", ...)",
+ first, second, fmt);

return p;

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/