5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Nikolay Aleksandrov razor@blackwall.org
[ Upstream commit 92c4ee25208d0f35dafc3213cdf355fbe449e078 ]
syzbot hit a use-after-free[1] which is caused because the bridge doesn't make sure that all previous garbage has been collected when removing a port. What happens is: CPU 1 CPU 2 start gc cycle remove port acquire gc lock first wait for lock call br_multicasg_gc() directly acquire lock now but free port the port can be freed while grp timers still running
Make sure all previous gc cycles have finished by using flush_work before freeing the port.
[1] BUG: KASAN: slab-use-after-free in br_multicast_port_group_expired+0x4c0/0x550 net/bridge/br_multicast.c:861 Read of size 8 at addr ffff888071d6d000 by task syz.5.1232/9699
CPU: 1 PID: 9699 Comm: syz.5.1232 Not tainted 6.10.0-rc5-syzkaller-00021-g24ca36a562d6 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024 Call Trace: <IRQ> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114 print_address_description mm/kasan/report.c:377 [inline] print_report+0xc3/0x620 mm/kasan/report.c:488 kasan_report+0xd9/0x110 mm/kasan/report.c:601 br_multicast_port_group_expired+0x4c0/0x550 net/bridge/br_multicast.c:861 call_timer_fn+0x1a3/0x610 kernel/time/timer.c:1792 expire_timers kernel/time/timer.c:1843 [inline] __run_timers+0x74b/0xaf0 kernel/time/timer.c:2417 __run_timer_base kernel/time/timer.c:2428 [inline] __run_timer_base kernel/time/timer.c:2421 [inline] run_timer_base+0x111/0x190 kernel/time/timer.c:2437
Reported-by: syzbot+263426984509be19c9a0@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=263426984509be19c9a0 Fixes: e12cec65b554 ("net: bridge: mcast: destroy all entries via gc") Signed-off-by: Nikolay Aleksandrov razor@blackwall.org Link: https://patch.msgid.link/20240802080730.3206303-1-razor@blackwall.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/bridge/br_multicast.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index 9765f9f9bf7ff..3cd2b648408d6 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -1890,16 +1890,14 @@ void br_multicast_del_port(struct net_bridge_port *port) { struct net_bridge *br = port->br; struct net_bridge_port_group *pg; - HLIST_HEAD(deleted_head); struct hlist_node *n;
/* Take care of the remaining groups, only perm ones should be left */ spin_lock_bh(&br->multicast_lock); hlist_for_each_entry_safe(pg, n, &port->mglist, mglist) br_multicast_find_del_pg(br, pg); - hlist_move_list(&br->mcast_gc_list, &deleted_head); spin_unlock_bh(&br->multicast_lock); - br_multicast_gc(&deleted_head); + flush_work(&br->mcast_gc_work); br_multicast_port_ctx_deinit(&port->multicast_ctx); free_percpu(port->mcast_stats); }