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sctp: deny peeloff operation on asocs with threads sleeping on it
commit 2dcab59 ("sctp: avoid BUG_ON on sctp_wait_for_sndbuf") attempted to avoid a BUG_ON call when the association being used for a sendmsg() is blocked waiting for more sndbuf and another thread did a peeloff operation on such asoc, moving it to another socket. As Ben Hutchings noticed, then in such case it would return without locking back the socket and would cause two unlocks in a row. Further analysis also revealed that it could allow a double free if the application managed to peeloff the asoc that is created during the sendmsg call, because then sctp_sendmsg() would try to free the asoc that was created only for that call. This patch takes another approach. It will deny the peeloff operation if there is a thread sleeping on the asoc, so this situation doesn't exist anymore. This avoids the issues described above and also honors the syscalls that are already being handled (it can be multiple sendmsg calls). Joint work with Xin Long. Fixes: 2dcab59 ("sctp: avoid BUG_ON on sctp_wait_for_sndbuf") Cc: Alexander Popov <email@example.com> Cc: Ben Hutchings <firstname.lastname@example.org> Signed-off-by: Marcelo Ricardo Leitner <email@example.com> Signed-off-by: Xin Long <firstname.lastname@example.org> Signed-off-by: David S. Miller <email@example.com>
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