5.15-stable review patch. If anyone has any objections, please let me know.
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From: Jiayuan Chen jiayuan.chen@linux.dev
[ Upstream commit 76be5fae32febb1fdb848ba09f78c4b2c76cb337 ]
We observed an issue from the latest selftest: sockmap_redir where sk_psock(psock->sk) != psock in the backlog. The root cause is the special behavior in sockmap_redir - it frequently performs map_update() and map_delete() on the same socket. During map_update(), we create a new psock and during map_delete(), we eventually free the psock via rcu_work in sk_psock_drop(). However, pending workqueues might still exist and not be processed yet. If users immediately perform another map_update(), a new psock will be allocated for the same sk, resulting in two psocks pointing to the same sk.
When the pending workqueue is later triggered, it uses the old psock to access sk for I/O operations, which is incorrect.
Timing Diagram:
cpu0 cpu1
map_update(sk): sk->psock = psock1 psock1->sk = sk map_delete(sk): rcu_work_free(psock1)
map_update(sk): sk->psock = psock2 psock2->sk = sk workqueue: wakeup with psock1, but the sk of psock1 doesn't belong to psock1 rcu_handler: clean psock1 free(psock1)
Previously, we used reference counting to address the concurrency issue between backlog and sock_map_close(). This logic remains necessary as it prevents the sk from being freed while processing the backlog. But this patch prevents pending backlogs from using a psock after it has been stopped.
Note: We cannot call cancel_delayed_work_sync() in map_delete() since this might be invoked in BPF context by BPF helper, and the function may sleep.
Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface") Signed-off-by: Jiayuan Chen jiayuan.chen@linux.dev Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Link: https://lore.kernel.org/bpf/20250609025908.79331-1-jiayuan.chen@linux.dev Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/skmsg.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 1d7cf920bf4e..68e5fd7aa128 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -648,6 +648,13 @@ static void sk_psock_backlog(struct work_struct *work) bool ingress; int ret;
+ /* If sk is quickly removed from the map and then added back, the old + * psock should not be scheduled, because there are now two psocks + * pointing to the same sk. + */ + if (!sk_psock_test_state(psock, SK_PSOCK_TX_ENABLED)) + return; + /* Increment the psock refcnt to synchronize with close(fd) path in * sock_map_close(), ensuring we wait for backlog thread completion * before sk_socket freed. If refcnt increment fails, it indicates