Re: [PATCH] mac80211: fix minstrel single-rate memory corruption

[Felix Fietkau <nbd@openwrt.org>]

Bob Copeland wrote:
> The minstrel rate controller periodically looks up rate indexes in
> a sampling table.  When accessing a specific row and column, minstrel
> correctly does a bounds check which, on the surface, appears to handle
> the case where mi->n_rates < 2.  However, mi->sample_idx is actually
> defined as an unsigned, so the right hand side is taken to be a huge
> positive number when negative, and the check will always fail.
> 
> Consequently, the RC will overrun the array and cause random memory
> corruption when communicating with a peer that has only a single rate.
> The max value of mi->sample_idx is around 25 so casting to int should
> have no ill effects.
> 
> Without the change, uptime is a few minutes under load with an AP
> that has a single hard-coded rate, and both the AP and STA could
> potentially crash.  With the change, both lasted 12 hours with a
> steady load.
> 
> Thanks to Ognjen Maric for providing the single-rate clue so I could
> reproduce this.
> 
> This fixes http://bugzilla.kernel.org/show_bug.cgi?id=12490 on the
> regression list (also http://bugzilla.kernel.org/show_bug.cgi?id=13000).
> 
> Cc: stable@kernel.org
> Reported-by: Sergey S. Kostyliov <rathamahata@gmail.com>
> Reported-by: Ognjen Maric <ognjen.maric@gmail.com>
> Signed-off-by: Bob Copeland <me@bobcopeland.com>
> ---
> 
> John & Felix, the patch itself may be too subtle so feel free to do it a
> different way.  However this is as minimal as it gets so I hope it can
> be applied quickly to stable, and mainline if not too late.
How about changing the type of sample_idx to signed instead of casting
it? It's just a cosmetic thing, so even if you leave at this you get my
Acked-by: Felix Fietkau <nbd@openwrt.org>

- Felix