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

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  [PATCH 08/14] lib/kasprintf.c: add sanity check to kvasprintf Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-11-23 22:40 +0100
    Re: [PATCH 08/14] lib/kasprintf.c: add sanity check to kvasprintf Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-11-24 00:20 +0100

#1275870 — [PATCH 08/14] 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>
---
 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);
 	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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#1275958

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
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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-- 
With Best Regards,
Andy Shevchenko
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