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SubjectRe: [PATCH 08/14] lib/kasprintf.c: add sanity check to kvasprintf
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On Mon, Nov 23, 2015 at 11:29 PM, Rasmus Villemoes
<linux@rasmusvillemoes.dk> wrote:
> 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>
> ---
> 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;

vsnprintf() returns plain int.
Perhaps change the type to follow the function.

> 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;
> }
> --
> 2.6.1
>
> --
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--
With Best Regards,
Andy Shevchenko


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