sctp: use the right sk after waking up from wait_buf sleep
Commit dfcb9f4f ("sctp: deny peeloff operation on asocs with threads sleeping on it") fixed the race between peeloff and wait sndbuf by checking waitqueue_active(&asoc->wait) in sctp_do_peeloff(). But it actually doesn't work, as even if waitqueue_active returns false the waiting sndbuf thread may still not yet hold sk lock. After asoc is peeled off, sk is not asoc->base.sk any more, then to hold the old sk lock couldn't make assoc safe to access. This patch is to fix this by changing to hold the new sk lock if sk is not asoc->base.sk, meanwhile, also set the sk in sctp_sendmsg with the new sk. With this fix, there is no more race between peeloff and waitbuf, the check 'waitqueue_active' in sctp_do_peeloff can be removed. Thanks Marcelo and Neil for making this clear. v1->v2: fix it by changing to lock the new sock instead of adding a flag in asoc. Suggested-by: NNeil Horman <nhorman@tuxdriver.com> Signed-off-by: NXin Long <lucien.xin@gmail.com> Acked-by: NNeil Horman <nhorman@tuxdriver.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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