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 4.4-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-4.4 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: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
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-4.4/sunrpc-fix-refcounting-problems-with-auth_gss-messages.patch