This is a note to let you know that I've just added the patch titled SUNRPC: fix refcounting problems with auth_gss messages. to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sunrpc-fix-refcounting-problems-with-auth_gss-messages.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 1cded9d2974fe4fe339fc0ccd6638b80d465ab2c Mon Sep 17 00:00:00 2001 From: NeilBrown <neilb@xxxxxxxx> Date: Mon, 5 Dec 2016 15:10:11 +1100 Subject: SUNRPC: fix refcounting problems with auth_gss messages. From: NeilBrown <neilb@xxxxxxxx> commit 1cded9d2974fe4fe339fc0ccd6638b80d465ab2c upstream. There are two problems with refcounting of auth_gss messages. First, the reference on the pipe->pipe list (taken by a call to rpc_queue_upcall()) is not counted. It seems to be assumed that a message in pipe->pipe will always also be in pipe->in_downcall, where it is correctly reference counted. However there is no guaranty of this. I have a report of a NULL dereferences in rpc_pipe_read() which suggests a msg that has been freed is still on the pipe->pipe list. One way I imagine this might happen is: - message is queued for uid=U and auth->service=S1 - rpc.gssd reads this message and starts processing. This removes the message from pipe->pipe - message is queued for uid=U and auth->service=S2 - rpc.gssd replies to the first message. gss_pipe_downcall() calls __gss_find_upcall(pipe, U, NULL) and it finds the *second* message, as new messages are placed at the head of ->in_downcall, and the service type is not checked. - This second message is removed from ->in_downcall and freed by gss_release_msg() (even though it is still on pipe->pipe) - rpc.gssd tries to read another message, and dereferences a pointer to this message that has just been freed. I fix this by incrementing the reference count before calling rpc_queue_upcall(), and decrementing it if that fails, or normally in gss_pipe_destroy_msg(). It seems strange that the reply doesn't target the message more precisely, but I don't know all the details. In any case, I think the reference counting irregularity became a measureable bug when the extra arg was added to __gss_find_upcall(), hence the Fixes: line below. The second problem is that if rpc_queue_upcall() fails, the new message is not freed. gss_alloc_msg() set the ->count to 1, gss_add_msg() increments this to 2, gss_unhash_msg() decrements to 1, then the pointer is discarded so the memory never gets freed. Fixes: 9130b8dbc6ac ("SUNRPC: allow for upcalls for same uid but different gss service") Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1011250 Signed-off-by: NeilBrown <neilb@xxxxxxxx> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/sunrpc/auth_gss/auth_gss.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/net/sunrpc/auth_gss/auth_gss.c +++ b/net/sunrpc/auth_gss/auth_gss.c @@ -541,9 +541,13 @@ gss_setup_upcall(struct gss_auth *gss_au return gss_new; gss_msg = gss_add_msg(gss_new); if (gss_msg == gss_new) { - int res = rpc_queue_upcall(gss_new->pipe, &gss_new->msg); + int res; + atomic_inc(&gss_msg->count); + res = rpc_queue_upcall(gss_new->pipe, &gss_new->msg); if (res) { gss_unhash_msg(gss_new); + atomic_dec(&gss_msg->count); + gss_release_msg(gss_new); gss_msg = ERR_PTR(res); } } else @@ -836,6 +840,7 @@ gss_pipe_destroy_msg(struct rpc_pipe_msg warn_gssd(); gss_release_msg(gss_msg); } + gss_release_msg(gss_msg); } static void gss_pipe_dentry_destroy(struct dentry *dir, Patches currently in stable-queue which might be from neilb@xxxxxxxx are queue-4.9/md-raid5-limit-request-size-according-to-implementation-limits.patch queue-4.9/sunrpc-fix-refcounting-problems-with-auth_gss-messages.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html