Patch "net/iucv: fix use after free in iucv_sock_close()" has been added to the 5.4-stable tree

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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);




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