This is a note to let you know that I've just added the patch titled
net/iucv: fix use after free in iucv_sock_close()
to the 5.4-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:
net-iucv-fix-use-after-free-in-iucv_sock_close.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1397547707af8d8e47a1138c858a0cc8bfafa5ef
Author: Alexandra Winter <wintera@xxxxxxxxxxxxx>
Date: Mon Jul 29 14:28:16 2024 +0200
net/iucv: fix use after free in iucv_sock_close()
[ Upstream commit f558120cd709682b739207b48cf7479fd9568431 ]
iucv_sever_path() is called from process context and from bh context.
iucv->path is used as indicator whether somebody else is taking care of
severing the path (or it is already removed / never existed).
This needs to be done with atomic compare and swap, otherwise there is a
small window where iucv_sock_close() will try to work with a path that has
already been severed and freed by iucv_callback_connrej() called by
iucv_tasklet_fn().
Example:
[452744.123844] Call Trace:
[452744.123845] ([<0000001e87f03880>] 0x1e87f03880)
[452744.123966] [<00000000d593001e>] iucv_path_sever+0x96/0x138
[452744.124330] [<000003ff801ddbca>] iucv_sever_path+0xc2/0xd0 [af_iucv]
[452744.124336] [<000003ff801e01b6>] iucv_sock_close+0xa6/0x310 [af_iucv]
[452744.124341] [<000003ff801e08cc>] iucv_sock_release+0x3c/0xd0 [af_iucv]
[452744.124345] [<00000000d574794e>] __sock_release+0x5e/0xe8
[452744.124815] [<00000000d5747a0c>] sock_close+0x34/0x48
[452744.124820] [<00000000d5421642>] __fput+0xba/0x268
[452744.124826] [<00000000d51b382c>] task_work_run+0xbc/0xf0
[452744.124832] [<00000000d5145710>] do_notify_resume+0x88/0x90
[452744.124841] [<00000000d5978096>] system_call+0xe2/0x2c8
[452744.125319] Last Breaking-Event-Address:
[452744.125321] [<00000000d5930018>] iucv_path_sever+0x90/0x138
[452744.125324]
[452744.125325] Kernel panic - not syncing: Fatal exception in interrupt
Note that bh_lock_sock() is not serializing the tasklet context against
process context, because the check for sock_owned_by_user() and
corresponding handling is missing.
Ideas for a future clean-up patch:
A) Correct usage of bh_lock_sock() in tasklet context, as described in
Link: https://lore.kernel.org/netdev/1280155406.2899.407.camel@edumazet-laptop/
Re-enqueue, if needed. This may require adding return values to the
tasklet functions and thus changes to all users of iucv.
B) Change iucv tasklet into worker and use only lock_sock() in af_iucv.
Fixes: 7d316b945352 ("af_iucv: remove IUCV-pathes completely")
Reviewed-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
Signed-off-by: Alexandra Winter <wintera@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20240729122818.947756-1-wintera@xxxxxxxxxxxxx
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index 652285191da1e..74cf37f17ea90 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -453,8 +453,8 @@ static void iucv_sever_path(struct sock *sk, int with_user_data)
struct iucv_sock *iucv = iucv_sk(sk);
struct iucv_path *path = iucv->path;
- if (iucv->path) {
- iucv->path = NULL;
+ /* Whoever resets the path pointer, must sever and free it. */
+ if (xchg(&iucv->path, NULL)) {
if (with_user_data) {
low_nmcpy(user_data, iucv->src_name);
high_nmcpy(user_data, iucv->dst_name);
