Patch "net/sched: act_api: fix possible infinite loop in tcf_idr_check_alloc()" has been added to the 6.9-stable tree

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

    net/sched: act_api: fix possible infinite loop in tcf_idr_check_alloc()

to the 6.9-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-sched-act_api-fix-possible-infinite-loop-in-tcf_.patch
and it can be found in the queue-6.9 subdirectory.

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



commit b08452fe569a379468dd7c1a5d2034c55b45ea08
Author: David Ruth <druth@xxxxxxxxxxxx>
Date:   Fri Jun 14 19:03:26 2024 +0000

    net/sched: act_api: fix possible infinite loop in tcf_idr_check_alloc()
    
    [ Upstream commit d864319871b05fadd153e0aede4811ca7008f5d6 ]
    
    syzbot found hanging tasks waiting on rtnl_lock [1]
    
    A reproducer is available in the syzbot bug.
    
    When a request to add multiple actions with the same index is sent, the
    second request will block forever on the first request. This holds
    rtnl_lock, and causes tasks to hang.
    
    Return -EAGAIN to prevent infinite looping, while keeping documented
    behavior.
    
    [1]
    
    INFO: task kworker/1:0:5088 blocked for more than 143 seconds.
    Not tainted 6.9.0-rc4-syzkaller-00173-g3cdb45594619 #0
    "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    task:kworker/1:0 state:D stack:23744 pid:5088 tgid:5088 ppid:2 flags:0x00004000
    Workqueue: events_power_efficient reg_check_chans_work
    Call Trace:
    <TASK>
    context_switch kernel/sched/core.c:5409 [inline]
    __schedule+0xf15/0x5d00 kernel/sched/core.c:6746
    __schedule_loop kernel/sched/core.c:6823 [inline]
    schedule+0xe7/0x350 kernel/sched/core.c:6838
    schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6895
    __mutex_lock_common kernel/locking/mutex.c:684 [inline]
    __mutex_lock+0x5b8/0x9c0 kernel/locking/mutex.c:752
    wiphy_lock include/net/cfg80211.h:5953 [inline]
    reg_leave_invalid_chans net/wireless/reg.c:2466 [inline]
    reg_check_chans_work+0x10a/0x10e0 net/wireless/reg.c:2481
    
    Fixes: 0190c1d452a9 ("net: sched: atomically check-allocate action")
    Reported-by: syzbot+b87c222546179f4513a7@xxxxxxxxxxxxxxxxxxxxxxxxx
    Closes: https://syzkaller.appspot.com/bug?extid=b87c222546179f4513a7
    Signed-off-by: David Ruth <druth@xxxxxxxxxxxx>
    Reviewed-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240614190326.1349786-1-druth@xxxxxxxxxxxx
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 9ee622fb1160f..2520708b06a12 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -830,7 +830,6 @@ int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index,
 	u32 max;
 
 	if (*index) {
-again:
 		rcu_read_lock();
 		p = idr_find(&idrinfo->action_idr, *index);
 
@@ -839,7 +838,7 @@ int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index,
 			 * index but did not assign the pointer yet.
 			 */
 			rcu_read_unlock();
-			goto again;
+			return -EAGAIN;
 		}
 
 		if (!p) {




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