| Message ID | 155871006055.18695.17031102947214023468.stgit@john-Precision-5820-Tower |
|---|---|
| State | Accepted |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [v2] bpf: sockmap, fix use after free from sleep in psock backlog workqueue | expand |
On 05/24/2019 05:01 PM, John Fastabend wrote: > Backlog work for psock (sk_psock_backlog) might sleep while waiting > for memory to free up when sending packets. However, while sleeping > the socket may be closed and removed from the map by the user space > side. > > This breaks an assumption in sk_stream_wait_memory, which expects the > wait queue to be still there when it wakes up resulting in a > use-after-free shown below. To fix his mark sendmsg as MSG_DONTWAIT > to avoid the sleep altogether. We already set the flag for the > sendpage case but we missed the case were sendmsg is used. > Sockmap is currently the only user of skb_send_sock_locked() so only > the sockmap paths should be impacted. > > ================================================================== > BUG: KASAN: use-after-free in remove_wait_queue+0x31/0x70 > Write of size 8 at addr ffff888069a0c4e8 by task kworker/0:2/110 > > CPU: 0 PID: 110 Comm: kworker/0:2 Not tainted 5.0.0-rc2-00335-g28f9d1a3d4fe-dirty #14 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-2.fc27 04/01/2014 > Workqueue: events sk_psock_backlog > Call Trace: > print_address_description+0x6e/0x2b0 > ? remove_wait_queue+0x31/0x70 > kasan_report+0xfd/0x177 > ? remove_wait_queue+0x31/0x70 > ? remove_wait_queue+0x31/0x70 > remove_wait_queue+0x31/0x70 > sk_stream_wait_memory+0x4dd/0x5f0 > ? sk_stream_wait_close+0x1b0/0x1b0 > ? wait_woken+0xc0/0xc0 > ? tcp_current_mss+0xc5/0x110 > tcp_sendmsg_locked+0x634/0x15d0 > ? tcp_set_state+0x2e0/0x2e0 > ? __kasan_slab_free+0x1d1/0x230 > ? kmem_cache_free+0x70/0x140 > ? sk_psock_backlog+0x40c/0x4b0 > ? process_one_work+0x40b/0x660 > ? worker_thread+0x82/0x680 > ? kthread+0x1b9/0x1e0 > ? ret_from_fork+0x1f/0x30 > ? check_preempt_curr+0xaf/0x130 > ? iov_iter_kvec+0x5f/0x70 [...] Applied, thanks!
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index e89be62..4a7c656 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -2337,6 +2337,7 @@ int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset, kv.iov_base = skb->data + offset; kv.iov_len = slen; memset(&msg, 0, sizeof(msg)); + msg.msg_flags = MSG_DONTWAIT; ret = kernel_sendmsg_locked(sk, &msg, &kv, 1, slen); if (ret <= 0)
Backlog work for psock (sk_psock_backlog) might sleep while waiting for memory to free up when sending packets. However, while sleeping the socket may be closed and removed from the map by the user space side. This breaks an assumption in sk_stream_wait_memory, which expects the wait queue to be still there when it wakes up resulting in a use-after-free shown below. To fix his mark sendmsg as MSG_DONTWAIT to avoid the sleep altogether. We already set the flag for the sendpage case but we missed the case were sendmsg is used. Sockmap is currently the only user of skb_send_sock_locked() so only the sockmap paths should be impacted. ================================================================== BUG: KASAN: use-after-free in remove_wait_queue+0x31/0x70 Write of size 8 at addr ffff888069a0c4e8 by task kworker/0:2/110 CPU: 0 PID: 110 Comm: kworker/0:2 Not tainted 5.0.0-rc2-00335-g28f9d1a3d4fe-dirty #14 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-2.fc27 04/01/2014 Workqueue: events sk_psock_backlog Call Trace: print_address_description+0x6e/0x2b0 ? remove_wait_queue+0x31/0x70 kasan_report+0xfd/0x177 ? remove_wait_queue+0x31/0x70 ? remove_wait_queue+0x31/0x70 remove_wait_queue+0x31/0x70 sk_stream_wait_memory+0x4dd/0x5f0 ? sk_stream_wait_close+0x1b0/0x1b0 ? wait_woken+0xc0/0xc0 ? tcp_current_mss+0xc5/0x110 tcp_sendmsg_locked+0x634/0x15d0 ? tcp_set_state+0x2e0/0x2e0 ? __kasan_slab_free+0x1d1/0x230 ? kmem_cache_free+0x70/0x140 ? sk_psock_backlog+0x40c/0x4b0 ? process_one_work+0x40b/0x660 ? worker_thread+0x82/0x680 ? kthread+0x1b9/0x1e0 ? ret_from_fork+0x1f/0x30 ? check_preempt_curr+0xaf/0x130 ? iov_iter_kvec+0x5f/0x70 ? kernel_sendmsg_locked+0xa0/0xe0 skb_send_sock_locked+0x273/0x3c0 ? skb_splice_bits+0x180/0x180 ? start_thread+0xe0/0xe0 ? update_min_vruntime.constprop.27+0x88/0xc0 sk_psock_backlog+0xb3/0x4b0 ? strscpy+0xbf/0x1e0 process_one_work+0x40b/0x660 worker_thread+0x82/0x680 ? process_one_work+0x660/0x660 kthread+0x1b9/0x1e0 ? __kthread_create_on_node+0x250/0x250 ret_from_fork+0x1f/0x30 Fixes: 20bf50de3028c ("skbuff: Function to send an skbuf on a socket") Reported-by: Jakub Sitnicki <jakub@cloudflare.com> Tested-by: Jakub Sitnicki <jakub@cloudflare.com> Signed-off-by: John Fastabend <john.fastabend@gmail.com> --- net/core/skbuff.c | 1 + 1 file changed, 1 insertion(+)