syzbot triggered an uninit value[1] error in bridge device's xmit path
by sending a short (less than ETH_HLEN bytes) skb. To fix it check if
we can actually pull that amount instead of assuming.
Tested with dropwatch:
drop at: br_dev_xmit+0xb93/0x12d0 [bridge] (0xffffffffc06739b3)
origin: software
timestamp: Mon May 13 11:31:53 2024 778214037 nsec
protocol: 0x88a8
length: 2
original length: 2
drop reason: PKT_TOO_SMALL
[1]
BUG: KMSAN: uninit-value in br_dev_xmit+0x61d/0x1cb0 net/bridge/br_device.c:65
br_dev_xmit+0x61d/0x1cb0 net/bridge/br_device.c:65
__netdev_start_xmit include/linux/netdevice.h:4903 [inline]
netdev_start_xmit include/linux/netdevice.h:4917 [inline]
xmit_one net/core/dev.c:3531 [inline]
dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3547
__dev_queue_xmit+0x34db/0x5350 net/core/dev.c:4341
dev_queue_xmit include/linux/netdevice.h:3091 [inline]
__bpf_tx_skb net/core/filter.c:2136 [inline]
__bpf_redirect_common net/core/filter.c:2180 [inline]
__bpf_redirect+0x14a6/0x1620 net/core/filter.c:2187
____bpf_clone_redirect net/core/filter.c:2460 [inline]
bpf_clone_redirect+0x328/0x470 net/core/filter.c:2432
___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997
__bpf_prog_run512+0xb5/0xe0 kernel/bpf/core.c:2238
bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
__bpf_prog_run include/linux/filter.h:657 [inline]
bpf_prog_run include/linux/filter.h:664 [inline]
bpf_test_run+0x499/0xc30 net/bpf/test_run.c:425
bpf_prog_test_run_skb+0x14ea/0x1f20 net/bpf/test_run.c:1058
bpf_prog_test_run+0x6b7/0xad0 kernel/bpf/syscall.c:4269
__sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5678
__do_sys_bpf kernel/bpf/syscall.c:5767 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5765 [inline]
__x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5765
x64_sys_call+0x96b/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:322
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+a63a1f6a062033cf0f40@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=a63a1f6a062033cf0f40
Signed-off-by: Nikolay Aleksandrov <razor@xxxxxxxxxxxxx>
---
net/bridge/br_device.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index c366ccc8b3db..ecac7886988b 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -27,6 +27,7 @@ EXPORT_SYMBOL_GPL(nf_br_ops);
/* net device transmit always called with BH disabled */
netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
{
+ enum skb_drop_reason reason = pskb_may_pull_reason(skb, ETH_HLEN);
struct net_bridge_mcast_port *pmctx_null = NULL;
struct net_bridge *br = netdev_priv(dev);
struct net_bridge_mcast *brmctx = &br->multicast_ctx;
@@ -38,6 +39,11 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
const unsigned char *dest;
u16 vid = 0;
+ if (unlikely(reason != SKB_NOT_DROPPED_YET)) {
+ kfree_skb_reason(skb, reason);
+ return NETDEV_TX_OK;
+ }
+
memset(skb->cb, 0, sizeof(struct br_input_skb_cb));
br_tc_skb_miss_set(skb, false);
--
2.44.0
