sctp: fix error handling on stream scheduler initialization

[ Upstream commit 4d1415811e492d9a8238f8a92dd0d51612c788e9 ]

It allocates the extended area for outbound streams only on sendmsg
calls, if they are not yet allocated.  When using the priority
stream scheduler, this initialization may imply into a subsequent
allocation, which may fail.  In this case, it was aborting the stream
scheduler initialization but leaving the ->ext pointer (allocated) in
there, thus in a partially initialized state.  On a subsequent call to
sendmsg, it would notice the ->ext pointer in there, and trip on
uninitialized stuff when trying to schedule the data chunk.

The fix is undo the ->ext initialization if the stream scheduler
initialization fails and avoid the partially initialized state.

Although syzkaller bisected this to commit 4ff40b86262b ("sctp: set
chunk transport correctly when it's a new asoc"), this bug was actually
introduced on the commit I marked below.

Reported-by: syzbot+c1a380d42b190ad1e559@syzkaller.appspotmail.com
Fixes: 5bbbbe32a431 ("sctp: introduce stream scheduler foundations")
Tested-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Neil Horman <nhorman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/sctp/stream.c b/net/sctp/stream.c
index b6bb68adac6e294b1d4caee5efaab8f93e6a683a..f72dfda4025d46b872829c0c2603ad774cf89afb 100644 (file)
--- a/net/sctp/stream.c
+++ b/net/sctp/stream.c
@@ -168,13 +168,20 @@ out:
 int sctp_stream_init_ext(struct sctp_stream *stream, __u16 sid)
 {
        struct sctp_stream_out_ext *soute;
+       int ret;
 
        soute = kzalloc(sizeof(*soute), GFP_KERNEL);
        if (!soute)
                return -ENOMEM;
        SCTP_SO(stream, sid)->ext = soute;
 
-       return sctp_sched_init_sid(stream, sid, GFP_KERNEL);
+       ret = sctp_sched_init_sid(stream, sid, GFP_KERNEL);
+       if (ret) {
+               kfree(SCTP_SO(stream, sid)->ext);
+               SCTP_SO(stream, sid)->ext = NULL;
+       }
+
+       return ret;
 }
 
 void sctp_stream_free(struct sctp_stream *stream)