CVE-2025-38166

In the Linux kernel, the following vulnerability has been resolved:

bpf: fix ktls panic with sockmap

[ 2172.936997] ————[ cut here ]———— [ 2172.936999] kernel BUG at lib/iov_iter.c:629! …… [ 2172.944996] PKRU: 55555554 [ 2172.945155] Call Trace: [ 2172.945299] [ 2172.945428] ? die+0x36/0x90 [ 2172.945601] ? do_trap+0xdd/0x100 [ 2172.945795] ? iov_iter_revert+0x178/0x180 [ 2172.946031] ? iov_iter_revert+0x178/0x180 [ 2172.946267] ? do_error_trap+0x7d/0x110 [ 2172.946499] ? iov_iter_revert+0x178/0x180 [ 2172.946736] ? exc_invalid_op+0x50/0x70 [ 2172.946961] ? iov_iter_revert+0x178/0x180 [ 2172.947197] ? asm_exc_invalid_op+0x1a/0x20 [ 2172.947446] ? iov_iter_revert+0x178/0x180 [ 2172.947683] ? iov_iter_revert+0x5c/0x180 [ 2172.947913] tls_sw_sendmsg_locked.isra.0+0x794/0x840 [ 2172.948206] tls_sw_sendmsg+0x52/0x80 [ 2172.948420] ? inet_sendmsg+0x1f/0x70 [ 2172.948634] __sys_sendto+0x1cd/0x200 [ 2172.948848] ? find_held_lock+0x2b/0x80 [ 2172.949072] ? syscall_trace_enter+0x140/0x270 [ 2172.949330] ? __lock_release.isra.0+0x5e/0x170 [ 2172.949595] ? find_held_lock+0x2b/0x80 [ 2172.949817] ? syscall_trace_enter+0x140/0x270 [ 2172.950211] ? lockdep_hardirqs_on_prepare+0xda/0x190 [ 2172.950632] ? ktime_get_coarse_real_ts64+0xc2/0xd0 [ 2172.951036] __x64_sys_sendto+0x24/0x30 [ 2172.951382] do_syscall_64+0x90/0x170 ……

After calling bpf_exec_tx_verdict(), the size of msg_pl->sg may increase, e.g., when the BPF program executes bpf_msg_push_data().

If the BPF program sets cork_bytes and sg.size is smaller than cork_bytes, it will return -ENOSPC and attempt to roll back to the non-zero copy logic. However, during rollback, msg->msg_iter is reset, but since msg_pl->sg.size has been increased, subsequent executions will exceed the actual size of msg_iter.

iov_iter_revert(&msg->msg_iter, msg_pl->sg.size - orig_size);

The changes in this commit are based on the following considerations:

1. When cork_bytes is set, rolling back to non-zero copy logic is pointless and can directly go to zero-copy logic.

2. We can not calculate the correct number of bytes to revert msg_iter.

Assume the original data is abcdefgh (8 bytes), and after 3 pushes by the BPF program, it becomes 11-byte data: abc?de?fgh?. Then, we set cork_bytes to 6, which means the first 6 bytes have been processed, and the remaining 5 bytes ?fgh? will be cached until the length meets the cork_bytes requirement.

However, some data in ?fgh? is not within sg->msg_iter (but in msg_pl instead), especially the data ? we pushed.

So it doesnt seem as simple as just reverting through an offset of msg_iter.

3. For non-TLS sockets in tcp_bpf_sendmsg, when a cork situation occurs, the user-space send() doesnt return an error, and the returned length is the same as the input length parameter, even if some data is cached.

Additionally, I saw that the current non-zero-copy logic for handling corking is written as:

line 1177 else if (ret != -EAGAIN) { if (ret == -ENOSPC) ret = 0; goto send_end;

So its ok to just return copied without error when a cork situation occurs.

Affected Software

References

• https://git.kernel.org/stable/c/2e36a81d388ec9c3f78b6223f7eda2088cd40adb
• https://git.kernel.org/stable/c/328cac3f9f8ae394748485e769a527518a9137c8
• https://git.kernel.org/stable/c/54a3ecaeeeae8176da8badbd7d72af1017032c39
• https://git.kernel.org/stable/c/57fbbe29e86042bbaa31c1a30d2afa16c427e3f7
• https://git.kernel.org/stable/c/603943f022a7fe5cc83ca7005faf34798fb7853f
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html