Re: [PATCH net v3] tipc: check minimum bearer MTU

From: Michal Kubecek <redacted>
Date: Fri,  2 Dec 2016 09:33:41 +0100 (CET)

Qian Zhang (张谦) reported a potential socket buffer overflow in
tipc_msg_build() which is also known as CVE-2016-8632: due to
insufficient checks, a buffer overflow can occur if MTU is too short for
even tipc headers. As anyone can set device MTU in a user/net namespace,
this issue can be abused by a regular user.

As agreed in the discussion on Ben Hutchings' original patch, we should
check the MTU at the moment a bearer is attached rather than for each
processed packet. We also need to repeat the check when bearer MTU is
adjusted to new device MTU. UDP case also needs a check to avoid
overflow when calculating bearer MTU.

Fixes: b97bf3fd8f6a ("[TIPC] Initial merge")
Signed-off-by: Michal Kubecek <redacted>
Reported-by: Qian Zhang (张谦) <redacted>

Applied and queued up for -stable, thanks.
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