Patch "rose: check NULL rose_loopback_neigh->loopback" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    rose: check NULL rose_loopback_neigh->loopback

to the 5.15-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:
     rose-check-null-rose_loopback_neigh-loopback.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 824e139333031c6c991817f8884ea2cbb1ba5cfb
Author: Bernard Pidoux <f6bvp@xxxxxxx>
Date:   Thu Aug 18 02:02:13 2022 +0200

    rose: check NULL rose_loopback_neigh->loopback
    
    [ Upstream commit 3c53cd65dece47dd1f9d3a809f32e59d1d87b2b8 ]
    
    Commit 3b3fd068c56e3fbea30090859216a368398e39bf added NULL check for
    `rose_loopback_neigh->dev` in rose_loopback_timer() but omitted to
    check rose_loopback_neigh->loopback.
    
    It thus prevents *all* rose connect.
    
    The reason is that a special rose_neigh loopback has a NULL device.
    
    /proc/net/rose_neigh illustrates it via rose_neigh_show() function :
    [...]
    seq_printf(seq, "%05d %-9s %-4s   %3d %3d  %3s     %3s %3lu %3lu",
               rose_neigh->number,
               (rose_neigh->loopback) ? "RSLOOP-0" : ax2asc(buf, &rose_neigh->callsign),
               rose_neigh->dev ? rose_neigh->dev->name : "???",
               rose_neigh->count,
    
    /proc/net/rose_neigh displays special rose_loopback_neigh->loopback as
    callsign RSLOOP-0:
    
    addr  callsign  dev  count use mode restart  t0  tf digipeaters
    00001 RSLOOP-0  ???      1   2  DCE     yes   0   0
    
    By checking rose_loopback_neigh->loopback, rose_rx_call_request() is called
    even in case rose_loopback_neigh->dev is NULL. This repairs rose connections.
    
    Verification with rose client application FPAC:
    
    FPAC-Node v 4.1.3 (built Aug  5 2022) for LINUX (help = h)
    F6BVP-4 (Commands = ?) : u
    Users - AX.25 Level 2 sessions :
    Port   Callsign     Callsign  AX.25 state  ROSE state  NetRom status
    axudp  F6BVP-5   -> F6BVP-9   Connected    Connected   ---------
    
    Fixes: 3b3fd068c56e ("rose: Fix Null pointer dereference in rose_send_frame()")
    Signed-off-by: Bernard Pidoux <f6bvp@xxxxxxx>
    Suggested-by: Francois Romieu <romieu@xxxxxxxxxxxxx>
    Cc: Thomas DL9SAU Osterried <thomas@xxxxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c
index 11c45c8c6c164..036d92c0ad794 100644
--- a/net/rose/rose_loopback.c
+++ b/net/rose/rose_loopback.c
@@ -96,7 +96,8 @@ static void rose_loopback_timer(struct timer_list *unused)
 		}
 
 		if (frametype == ROSE_CALL_REQUEST) {
-			if (!rose_loopback_neigh->dev) {
+			if (!rose_loopback_neigh->dev &&
+			    !rose_loopback_neigh->loopback) {
 				kfree_skb(skb);
 				continue;
 			}