The kernel crash was caused by a BPF program attached to the "lsm_cgroup/socket_sock_rcv_skb" hook, which performed a call to `bpf_setsockopt()` in order to set the TCP_NODELAY flag as an example. Flags like TCP_NODELAY can prompt the kernel to flush a socket's outgoing queue, and this hook "lsm_cgroup/socket_sock_rcv_skb" is frequently triggered by softirqs. The issue was that in certain circumstances, when `tcp_write_xmit()` was called to flush the queue, it would also allow BH (bottom-half) to run. This could lead to our program attempting to flush the same socket recursively, which caused a `skbuf` to be unlinked twice. `security_sock_rcv_skb()` is triggered by `tcp_filter()`. This occurs before the sock ownership is checked in `tcp_v4_rcv()`. Consequently, if a bpf program runs on `security_sock_rcv_skb()` while under softirq conditions, it may not possess the lock needed for `bpf_setsoppt()`, thus presenting an issue. The patch fixes this issue by ensuring that a BPF program attached to the "lsm_cgroup/socket_sock_rcv_skb" hook is not allowed to call `bpf_setsockopt()`. The differences from v1 are - changing commit log to explain holding the lock of the sock, - emphasizing that TCP_NODELAY is not the only flag, and - adding the fixes tag. v1: https://lore.kernel.org/bpf/20230125000244.1109228-1-kuifeng@xxxxxxxx/ Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxxxx> Fixes: 9113d7e48e91 ("bpf: expose bpf_{g,s}etsockopt to lsm cgroup") --- kernel/bpf/bpf_lsm.c | 1 - 1 file changed, 1 deletion(-) diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c index a4a41ee3e80b..e14c822f8911 100644 --- a/kernel/bpf/bpf_lsm.c +++ b/kernel/bpf/bpf_lsm.c @@ -51,7 +51,6 @@ BTF_SET_END(bpf_lsm_current_hooks) */ BTF_SET_START(bpf_lsm_locked_sockopt_hooks) #ifdef CONFIG_SECURITY_NETWORK -BTF_ID(func, bpf_lsm_socket_sock_rcv_skb) BTF_ID(func, bpf_lsm_sock_graft) BTF_ID(func, bpf_lsm_inet_csk_clone) BTF_ID(func, bpf_lsm_inet_conn_established) -- 2.30.2
