On 24/02/2020 10:38, syzbot wrote:> Hello, > > syzbot found the following crash on: > > HEAD commit: 8bbbc5cf kmsan: don't compile memmove > git tree: https://github.com/google/kmsan.git master > console output: https://syzkaller.appspot.com/x/log.txt?x=14d9a3d9e00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=cd0e9a6b0e555cc3 > dashboard link: https://syzkaller.appspot.com/bug?extid=18c8b623c66fc198c493 > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > userspace arch: i386 > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+18c8b623c66fc198c493 at syzkaller.appspotmail.com >br_allowed_ingress() can call skb_vlan_untag() which does pskb_may_pull() and so the cached eth header can become invalid. I'll prepare a fix. Cheers, Nik> ====================================================> BUG: KMSAN: uninit-value in br_dev_xmit+0x99a/0x1730 net/bridge/br_device.c:64 > CPU: 0 PID: 14704 Comm: syz-executor.1 Not tainted 5.6.0-rc2-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x1c9/0x220 lib/dump_stack.c:118 > kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118 > __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215 > br_dev_xmit+0x99a/0x1730 net/bridge/br_device.c:64 > __netdev_start_xmit include/linux/netdevice.h:4524 [inline] > netdev_start_xmit include/linux/netdevice.h:4538 [inline] > xmit_one net/core/dev.c:3470 [inline] > dev_hard_start_xmit+0x531/0xab0 net/core/dev.c:3486 > __dev_queue_xmit+0x37de/0x4220 net/core/dev.c:4063 > dev_queue_xmit+0x4b/0x60 net/core/dev.c:4096 > __bpf_tx_skb net/core/filter.c:2061 [inline] > __bpf_redirect_common net/core/filter.c:2100 [inline] > __bpf_redirect+0x11d5/0x1440 net/core/filter.c:2107 > ____bpf_clone_redirect net/core/filter.c:2140 [inline] > bpf_clone_redirect+0x466/0x620 net/core/filter.c:2112 > bpf_prog_a481c1313990ee2c+0x5e0/0x1000 > bpf_dispatcher_nopfunc include/linux/bpf.h:521 [inline] > bpf_test_run+0x60c/0xe50 net/bpf/test_run.c:48 > bpf_prog_test_run_skb+0xcab/0x24a0 net/bpf/test_run.c:388 > bpf_prog_test_run kernel/bpf/syscall.c:2572 [inline] > __do_sys_bpf+0xa684/0x13510 kernel/bpf/syscall.c:3414 > __se_sys_bpf kernel/bpf/syscall.c:3355 [inline] > __ia32_sys_bpf+0xdb/0x120 kernel/bpf/syscall.c:3355 > do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline] > do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410 > entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139 > RIP: 0023:0xf7f79d99 > Code: 90 e8 0b 00 00 00 f3 90 0f ae e8 eb f9 8d 74 26 00 89 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90 > RSP: 002b:00000000f5d740cc EFLAGS: 00000296 ORIG_RAX: 0000000000000165 > RAX: ffffffffffffffda RBX: 000000000000000a RCX: 0000000020000140 > RDX: 0000000000000040 RSI: 0000000000000000 RDI: 0000000000000000 > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > > Uninit was created at: > kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline] > kmsan_internal_poison_shadow+0x66/0xd0 mm/kmsan/kmsan.c:127 > kmsan_slab_alloc+0x8a/0xe0 mm/kmsan/kmsan_hooks.c:82 > slab_alloc_node mm/slub.c:2793 [inline] > __kmalloc_node_track_caller+0xb40/0x1200 mm/slub.c:4401 > __kmalloc_reserve net/core/skbuff.c:142 [inline] > pskb_expand_head+0x20b/0x1b00 net/core/skbuff.c:1629 > skb_ensure_writable+0x3ea/0x490 net/core/skbuff.c:5453 > __bpf_try_make_writable net/core/filter.c:1635 [inline] > bpf_try_make_writable net/core/filter.c:1641 [inline] > bpf_try_make_head_writable net/core/filter.c:1649 [inline] > ____bpf_clone_redirect net/core/filter.c:2134 [inline] > bpf_clone_redirect+0x251/0x620 net/core/filter.c:2112 > bpf_prog_a481c1313990ee2c+0x5e0/0x1000 > bpf_dispatcher_nopfunc include/linux/bpf.h:521 [inline] > bpf_test_run+0x60c/0xe50 net/bpf/test_run.c:48 > bpf_prog_test_run_skb+0xcab/0x24a0 net/bpf/test_run.c:388 > bpf_prog_test_run kernel/bpf/syscall.c:2572 [inline] > __do_sys_bpf+0xa684/0x13510 kernel/bpf/syscall.c:3414 > __se_sys_bpf kernel/bpf/syscall.c:3355 [inline] > __ia32_sys_bpf+0xdb/0x120 kernel/bpf/syscall.c:3355 > do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline] > do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410 > entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139 > ====================================================> > > --- > This bug is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller at googlegroups.com. > > syzbot will keep track of this bug report. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. >
Nikolay Aleksandrov
2020-Feb-24 13:07 UTC
[Bridge] [PATCH net] net: bridge: fix stale eth hdr pointer in br_dev_xmit
In br_dev_xmit() we perform vlan filtering in br_allowed_ingress() but
if the packet has the vlan header inside (e.g. bridge with disabled
tx-vlan-offload) then the vlan filtering code will use skb_vlan_untag()
to extract the vid before filtering which in turn calls pskb_may_pull()
and we may end up with a stale eth pointer. Moreover the cached eth header
pointer will generally be wrong after that operation. Remove the eth header
caching and just use eth_hdr() directly, the compiler does the right thing
and calculates it only once so we don't lose anything.
Reported-by: syzbot+18c8b623c66fc198c493 at syzkaller.appspotmail.com
Fixes: 057658cb33fb ("bridge: suppress arp pkts on BR_NEIGH_SUPPRESS
ports")
Signed-off-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
---
net/bridge/br_device.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index dc3d2c1dd9d5..0e3dbc5f3c34 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -34,7 +34,6 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device
*dev)
const struct nf_br_ops *nf_ops;
u8 state = BR_STATE_FORWARDING;
const unsigned char *dest;
- struct ethhdr *eth;
u16 vid = 0;
rcu_read_lock();
@@ -54,15 +53,14 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct
net_device *dev)
BR_INPUT_SKB_CB(skb)->frag_max_size = 0;
skb_reset_mac_header(skb);
- eth = eth_hdr(skb);
skb_pull(skb, ETH_HLEN);
if (!br_allowed_ingress(br, br_vlan_group_rcu(br), skb, &vid, &state))
goto out;
if (IS_ENABLED(CONFIG_INET) &&
- (eth->h_proto == htons(ETH_P_ARP) ||
- eth->h_proto == htons(ETH_P_RARP)) &&
+ (eth_hdr(skb)->h_proto == htons(ETH_P_ARP) ||
+ eth_hdr(skb)->h_proto == htons(ETH_P_RARP)) &&
br_opt_get(br, BROPT_NEIGH_SUPPRESS_ENABLED)) {
br_do_proxy_suppress_arp(skb, br, vid, NULL);
} else if (IS_ENABLED(CONFIG_IPV6) &&
--
2.24.1