4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Marcelo Ricardo Leitner marcelo.leitner@gmail.com
[ Upstream commit b336decab22158937975293aea79396525f92bb3 ]
syzbot reported an use-after-free involving sctp_id2asoc. Dmitry Vyukov helped to root cause it and it is because of reading the asoc after it was freed:
CPU 1 CPU 2 (working on socket 1) (working on socket 2) sctp_association_destroy sctp_id2asoc spin lock grab the asoc from idr spin unlock spin lock remove asoc from idr spin unlock free(asoc) if asoc->base.sk != sk ... [*]
This can only be hit if trying to fetch asocs from different sockets. As we have a single IDR for all asocs, in all SCTP sockets, their id is unique on the system. An application can try to send stuff on an id that matches on another socket, and the if in [*] will protect from such usage. But it didn't consider that as that asoc may belong to another socket, it may be freed in parallel (read: under another socket lock).
We fix it by moving the checks in [*] into the protected region. This fixes it because the asoc cannot be freed while the lock is held.
Reported-by: syzbot+c7dd55d7aec49d48e49a@syzkaller.appspotmail.com Acked-by: Dmitry Vyukov dvyukov@google.com Signed-off-by: Marcelo Ricardo Leitner marcelo.leitner@gmail.com Acked-by: Neil Horman nhorman@tuxdriver.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/sctp/socket.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
--- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -248,11 +248,10 @@ struct sctp_association *sctp_id2assoc(s
spin_lock_bh(&sctp_assocs_id_lock); asoc = (struct sctp_association *)idr_find(&sctp_assocs_id, (int)id); + if (asoc && (asoc->base.sk != sk || asoc->base.dead)) + asoc = NULL; spin_unlock_bh(&sctp_assocs_id_lock);
- if (!asoc || (asoc->base.sk != sk) || asoc->base.dead) - return NULL; - return asoc; }