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authorMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>2018-10-16 15:18:17 -0300
committerDavid S. Miller <davem@davemloft.net>2018-10-17 22:11:14 -0700
commitb336decab22158937975293aea79396525f92bb3 (patch)
tree377447f6b7b0a37a2f117c1308bc22a5fa906250 /net
parent9675931e6b65d160d16bcc9472c1acef15524def (diff)
downloadlinux-b336decab22158937975293aea79396525f92bb3.tar.bz2
sctp: fix race on sctp_id2asoc
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>
Diffstat (limited to 'net')
-rw-r--r--net/sctp/socket.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index e25a20fc629a..bba877a0205b 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -271,11 +271,10 @@ struct sctp_association *sctp_id2assoc(struct sock *sk, sctp_assoc_t id)
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;
}