init_dummy_netdev() leaves its netdev_ops pointer zeroed. This leads to a NULL pointer dereference when sk_busy_loop fires against an iwlwifi wireless adapter and checks napi->dev->netdev_ops->ndo_busy_poll.

Avoid this by ensuring napi->dev->netdev_ops is valid before following the pointer, avoiding the following panic when busy polling on a dummy netdev:

BUG: unable to handle kernel NULL pointer dereference at 00000000000000c8 IP: [<ffffffff817b4b72>] sk_busy_loop+0x92/0x2f0 Call Trace: [<ffffffff815a3134>] ? uart_write_room+0x74/0xf0 [<ffffffff817964a9>] sock_poll+0x99/0xa0 [<ffffffff81223142>] do_sys_poll+0x2e2/0x520 [<ffffffff8118d3fc>] ? get_page_from_freelist+0x3bc/0xa30 [<ffffffff810ada22>] ? update_curr+0x62/0x140 [<ffffffff811ea671>] ? __slab_free+0xa1/0x2a0 [<ffffffff811ea671>] ? __slab_free+0xa1/0x2a0 [<ffffffff8179dbb1>] ? skb_free_head+0x21/0x30 [<ffffffff81221bd0>] ? poll_initwait+0x50/0x50 [<ffffffff811eaa36>] ? kmem_cache_free+0x1c6/0x1e0 [<ffffffff815a4884>] ? uart_write+0x124/0x1d0 [<ffffffff810bd1cd>] ? remove_wait_queue+0x4d/0x60 [<ffffffff810bd224>] ? __wake_up+0x44/0x50 [<ffffffff81582731>] ? tty_write_unlock+0x31/0x40 [<ffffffff8158c5c6>] ? tty_ldisc_deref+0x16/0x20 [<ffffffff81584820>] ? tty_write+0x1e0/0x2f0 [<ffffffff81587e50>] ? process_echoes+0x80/0x80 [<ffffffff8120c17b>] ? __vfs_write+0x2b/0x130 [<ffffffff8120d09a>] ? vfs_write+0x15a/0x1a0 [<ffffffff81223455>] SyS_poll+0x75/0x100 [<ffffffff819a6524>] entry_SYSCALL_64_fastpath+0x24/0xcf

Commit 79e7fff47b7b ("net: remove support for per driver ndo_busy_poll()") indirectly fixed this upstream in linux-4.11 by removing the offending pointer usage. No other users of napi->dev touch its netdev_ops.

Fixes: 8b80cda536ea ("net: rename include/net/ll_poll.h to include/net/busy_poll.h") # 4.4.y Signed-off-by: Josh Elsasser jelsasser@appneta.com ---

This is a straightforward backport of the 4.9.y fix[1] for this crash, which doesn't apply to the older LTS releases. Only build-tested on 4.4.y, as I don't have access to wireless hardware and firmware that runs on older LTS kernels.

[1]: https://lore.kernel.org/stable/20190701234143.72631-1-jelsasser@appneta.com/...

include/net/busy_poll.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h index 1d67fb6b23a0..6d238506d49b 100644 --- a/include/net/busy_poll.h +++ b/include/net/busy_poll.h @@ -93,7 +93,7 @@ static inline bool sk_busy_loop(struct sock *sk, int nonblock) goto out;

ops = napi->dev->netdev_ops; - if (!ops->ndo_busy_poll) + if (!ops || !ops->ndo_busy_poll) goto out;

do {