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SubjectRe: [PATCH 2/8] libertas: change snprintf to scnprintf for possible overflow
Willy Tarreau <> writes:

> From: Silvio Cesare <>
> Change snprintf to scnprintf. There are generally two cases where using
> snprintf causes problems.
> 1) Uses of size += snprintf(buf, SIZE - size, fmt, ...)
> In this case, if snprintf would have written more characters than what the
> buffer size (SIZE) is, then size will end up larger than SIZE. In later
> uses of snprintf, SIZE - size will result in a negative number, leading
> to problems. Note that size might already be too large by using
> size = snprintf before the code reaches a case of size += snprintf.
> 2) If size is ultimately used as a length parameter for a copy back to user
> space, then it will potentially allow for a buffer overflow and information
> disclosure when size is greater than SIZE. When the size is used to index
> the buffer directly, we can have memory corruption. This also means when
> size = snprintf... is used, it may also cause problems since size may become
> large. Copying to userspace is mitigated by the HARDENED_USERCOPY kernel
> configuration.
> The solution to these issues is to use scnprintf which returns the number of
> characters actually written to the buffer, so the size variable will never
> exceed SIZE.
> Signed-off-by: Silvio Cesare <>
> Cc: Kalle Valo <>
> Cc: Dan Carpenter <>
> Cc: Kees Cook <>
> Cc: Will Deacon <>
> Cc: Greg KH <>
> Signed-off-by: Willy Tarreau <>

I don't see any mention about which tree this should go to. Can I take
this to wireless-drivers-next?

Kalle Valo

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