Re: [PATCH 2/8] libertas: change snprintf to scnprintf for possible overflow
From: Kalle Valo
Date: Wed Jan 16 2019 - 11:40:38 EST
Willy Tarreau <w@xxxxxx> writes:
> On Tue, Jan 15, 2019 at 07:55:36AM +0200, Kalle Valo wrote:
>> Willy Tarreau <w@xxxxxx> writes:
>> > From: Silvio Cesare <silvio.cesare@xxxxxxxxx>
>> > 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 <silvio.cesare@xxxxxxxxx>
>> > Cc: Kalle Valo <kvalo@xxxxxxxxxxxxxx>
>> > Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
>> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> > Cc: Will Deacon <will.deacon@xxxxxxx>
>> > Cc: Greg KH <greg@xxxxxxxxx>
>> > Signed-off-by: Willy Tarreau <w@xxxxxx>
>> I don't see any mention about which tree this should go to. Can I take
>> this to wireless-drivers-next?
> Possibly. It addresses a small memory disclosure issue when using debugfs,
> and as such it should probably also be submitted to stable branches, so
> please use the most suitable tree that doesn't add too much extra delay.
Ok, I'll queue this for 5.0 and apply it to wireless-drivers instead.