diff options
| author | Eyal Birger <eyal.birger@gmail.com> | 2022-04-20 19:52:19 +0300 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2022-04-22 17:45:25 +0200 |
| commit | b02d196c44ead1a5949729be9ff08fe781c3e48a (patch) | |
| tree | 9705f30c2900f9b67bf47fd25db4940ae7f6b97e /net | |
| parent | 425d239379db03d514cb1c476bfe7c320bb89dfc (diff) | |
bpf, lwt: Fix crash when using bpf_skb_set_tunnel_key() from bpf_xmit lwt hook
xmit_check_hhlen() observes the dst for getting the device hard header
length to make sure a modified packet can fit. When a helper which changes
the dst - such as bpf_skb_set_tunnel_key() - is called as part of the
xmit program the accessed dst is no longer valid.
This leads to the following splat:
BUG: kernel NULL pointer dereference, address: 00000000000000de
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 0 PID: 798 Comm: ping Not tainted 5.18.0-rc2+ #103
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
RIP: 0010:bpf_xmit+0xfb/0x17f
Code: c6 c0 4d cd 8e 48 c7 c7 7d 33 f0 8e e8 42 09 fb ff 48 8b 45 58 48 8b 95 c8 00 00 00 48 2b 95 c0 00 00 00 48 83 e0 fe 48 8b 00 <0f> b7 80 de 00 00 00 39 c2 73 22 29 d0 b9 20 0a 00 00 31 d2 48 89
RSP: 0018:ffffb148c0bc7b98 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000240008 RCX: 0000000000000000
RDX: 0000000000000010 RSI: 00000000ffffffea RDI: 00000000ffffffff
RBP: ffff922a828a4e00 R08: ffffffff8f1350e8 R09: 00000000ffffdfff
R10: ffffffff8f055100 R11: ffffffff8f105100 R12: 0000000000000000
R13: ffff922a828a4e00 R14: 0000000000000040 R15: 0000000000000000
FS: 00007f414e8f0080(0000) GS:ffff922afdc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000000de CR3: 0000000002d80006 CR4: 0000000000370ef0
Call Trace:
<TASK>
lwtunnel_xmit.cold+0x71/0xc8
ip_finish_output2+0x279/0x520
? __ip_finish_output.part.0+0x21/0x130
Fix by fetching the device hard header length before running the BPF code.
Fixes: 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel infrastructure")
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220420165219.1755407-1-eyal.birger@gmail.com
Diffstat (limited to 'net')
| -rw-r--r-- | net/core/lwt_bpf.c | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c index 349480ef68a5..8b6b5e72b217 100644 --- a/net/core/lwt_bpf.c +++ b/net/core/lwt_bpf.c @@ -159,10 +159,8 @@ static int bpf_output(struct net *net, struct sock *sk, struct sk_buff *skb) return dst->lwtstate->orig_output(net, sk, skb); } -static int xmit_check_hhlen(struct sk_buff *skb) +static int xmit_check_hhlen(struct sk_buff *skb, int hh_len) { - int hh_len = skb_dst(skb)->dev->hard_header_len; - if (skb_headroom(skb) < hh_len) { int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb)); @@ -274,6 +272,7 @@ static int bpf_xmit(struct sk_buff *skb) bpf = bpf_lwt_lwtunnel(dst->lwtstate); if (bpf->xmit.prog) { + int hh_len = dst->dev->hard_header_len; __be16 proto = skb->protocol; int ret; @@ -291,7 +290,7 @@ static int bpf_xmit(struct sk_buff *skb) /* If the header was expanded, headroom might be too * small for L2 header to come, expand as needed. */ - ret = xmit_check_hhlen(skb); + ret = xmit_check_hhlen(skb, hh_len); if (unlikely(ret)) return ret; |