[PATCH AUTOSEL 5.2 034/123] bpf: fix access to skb_shared_info->gso_segs
From: Sasha Levin <sashal@kernel.org>
Date: 2019-08-14 02:11:57
Also in:
bpf, lkml, stable
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Eric Dumazet <edumazet@google.com>
[ Upstream commit 06a22d897d82f12776d44dbf0850f5895469cb2a ]
It is possible we reach bpf_convert_ctx_access() with
si->dst_reg == si->src_reg
Therefore, we need to load BPF_REG_AX before eventually
mangling si->src_reg.
syzbot generated this x86 code :
3: 55 push %rbp
4: 48 89 e5 mov %rsp,%rbp
7: 48 81 ec 00 00 00 00 sub $0x0,%rsp // Might be avoided ?
e: 53 push %rbx
f: 41 55 push %r13
11: 41 56 push %r14
13: 41 57 push %r15
15: 6a 00 pushq $0x0
17: 31 c0 xor %eax,%eax
19: 48 8b bf c0 00 00 00 mov 0xc0(%rdi),%rdi
20: 44 8b 97 bc 00 00 00 mov 0xbc(%rdi),%r10d
27: 4c 01 d7 add %r10,%rdi
2a: 48 0f b7 7f 06 movzwq 0x6(%rdi),%rdi // Crash
2f: 5b pop %rbx
30: 41 5f pop %r15
32: 41 5e pop %r14
34: 41 5d pop %r13
36: 5b pop %rbx
37: c9 leaveq
38: c3 retq
Fixes: d9ff286a0f59 ("bpf: allow BPF programs access skb_shared_info->gso_segs field")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <redacted>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/filter.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index f681fb772940c..534c310bb0893 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -7325,12 +7325,12 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type, case offsetof(struct __sk_buff, gso_segs): /* si->dst_reg = skb_shinfo(SKB); */ #ifdef NET_SKBUFF_DATA_USES_OFFSET - *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, head), - si->dst_reg, si->src_reg, - offsetof(struct sk_buff, head)); *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, end), BPF_REG_AX, si->src_reg, offsetof(struct sk_buff, end)); + *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, head), + si->dst_reg, si->src_reg, + offsetof(struct sk_buff, head)); *insn++ = BPF_ALU64_REG(BPF_ADD, si->dst_reg, BPF_REG_AX); #else *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, end),
--
2.20.1