Commit 8e2a2bfd authored Jan 15, 2016 by Rasmus Villemoes Committed by Linus Torvalds Jan 16, 2016

lib/kasprintf.c: add sanity check to kvasprintf



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@rasmusvillemoes.dk>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Joe Perches <joe@perches.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Maurizio Lombardi <mlombard@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 4d72ba01

lib/kasprintf.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -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);
		va_end(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;
		}

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