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Subject[PATCH 5.1 014/138] bpf: sockmap, restore sk_write_space when psock gets dropped
Date
[ Upstream commit 186bcc3dcd106dc52d706117f912054b616666e1 ]

Once psock gets unlinked from its sock (sk_psock_drop), user-space can
still trigger a call to sk->sk_write_space by setting TCP_NOTSENT_LOWAT
socket option. This causes a null-ptr-deref because we try to read
psock->saved_write_space from sk_psock_write_space:

==================================================================
BUG: KASAN: null-ptr-deref in sk_psock_write_space+0x69/0x80
Read of size 8 at addr 00000000000001a0 by task sockmap-echo/131

CPU: 0 PID: 131 Comm: sockmap-echo Not tainted 5.2.0-rc1-00094-gf49aa1de9836 #81
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
?-20180724_192412-buildhw-07.phx2.fedoraproject.org-1.fc29 04/01/2014
Call Trace:
? sk_psock_write_space+0x69/0x80
__kasan_report.cold.2+0x5/0x3f
? sk_psock_write_space+0x69/0x80
kasan_report+0xe/0x20
sk_psock_write_space+0x69/0x80
tcp_setsockopt+0x69a/0xfc0
? tcp_shutdown+0x70/0x70
? fsnotify+0x5b0/0x5f0
? remove_wait_queue+0x90/0x90
? __fget_light+0xa5/0xf0
__sys_setsockopt+0xe6/0x180
? sockfd_lookup_light+0xb0/0xb0
? vfs_write+0x195/0x210
? ksys_write+0xc9/0x150
? __x64_sys_read+0x50/0x50
? __bpf_trace_x86_fpu+0x10/0x10
__x64_sys_setsockopt+0x61/0x70
do_syscall_64+0xc5/0x520
? vmacache_find+0xc0/0x110
? syscall_return_slowpath+0x110/0x110
? handle_mm_fault+0xb4/0x110
? entry_SYSCALL_64_after_hwframe+0x3e/0xbe
? trace_hardirqs_off_caller+0x4b/0x120
? trace_hardirqs_off_thunk+0x1a/0x3a
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f2e5e7cdcce
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb b1 66 2e 0f 1f 84 00 00 00 00 00
0f 1f 44 00 00 f3 0f 1e fa 49 89 ca b8 36 00 00 00 0f 05 <48> 3d 01 f0 ff
ff 73 01 c3 48 8b 0d 8a 11 0c 00 f7 d8 64 89 01 48
RSP: 002b:00007ffed011b778 EFLAGS: 00000206 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f2e5e7cdcce
RDX: 0000000000000019 RSI: 0000000000000006 RDI: 0000000000000007
RBP: 00007ffed011b790 R08: 0000000000000004 R09: 00007f2e5e84ee80
R10: 00007ffed011b788 R11: 0000000000000206 R12: 00007ffed011b78c
R13: 00007ffed011b788 R14: 0000000000000007 R15: 0000000000000068
==================================================================

Restore the saved sk_write_space callback when psock is being dropped to
fix the crash.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/skmsg.h | 2 ++
1 file changed, 2 insertions(+)

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 178a3933a71b..50ced8aba9db 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -351,6 +351,8 @@ static inline void sk_psock_update_proto(struct sock *sk,
static inline void sk_psock_restore_proto(struct sock *sk,
struct sk_psock *psock)
{
+ sk->sk_write_space = psock->saved_write_space;
+
if (psock->sk_proto) {
sk->sk_prot = psock->sk_proto;
psock->sk_proto = NULL;
--
2.20.1


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