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Date: Mon, 30 Oct 2023 08:45:29 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, syzbot <syzkaller@...glegroups.com>, 
	Dmitry Safonov <dima@...sta.com>, Francesco Ruggeri <fruggeri@...sta.com>, David Ahern <dsahern@...nel.org>
Subject: [PATCH net] net/tcp: fix possible out-of-bounds reads in tcp_hash_fail()

syzbot managed to trigger a fault by sending TCP packets
with all flags being set.

BUG: KASAN: stack-out-of-bounds in string_nocheck lib/vsprintf.c:645 [inline]
BUG: KASAN: stack-out-of-bounds in string+0x394/0x3d0 lib/vsprintf.c:727
Read of size 1 at addr ffffc9000397f3f5 by task syz-executor299/5039

CPU: 1 PID: 5039 Comm: syz-executor299 Not tainted 6.6.0-rc7-syzkaller-02075-g55c900477f5b #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xc4/0x620 mm/kasan/report.c:475
kasan_report+0xda/0x110 mm/kasan/report.c:588
string_nocheck lib/vsprintf.c:645 [inline]
string+0x394/0x3d0 lib/vsprintf.c:727
vsnprintf+0xc5f/0x1870 lib/vsprintf.c:2818
vprintk_store+0x3a0/0xb80 kernel/printk/printk.c:2191
vprintk_emit+0x14c/0x5f0 kernel/printk/printk.c:2288
vprintk+0x7b/0x90 kernel/printk/printk_safe.c:45
_printk+0xc8/0x100 kernel/printk/printk.c:2332
tcp_inbound_hash.constprop.0+0xdb2/0x10d0 include/net/tcp.h:2760
tcp_v6_rcv+0x2b31/0x34d0 net/ipv6/tcp_ipv6.c:1882
ip6_protocol_deliver_rcu+0x33b/0x13d0 net/ipv6/ip6_input.c:438
ip6_input_finish+0x14f/0x2f0 net/ipv6/ip6_input.c:483
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ip6_input+0xce/0x440 net/ipv6/ip6_input.c:492
dst_input include/net/dst.h:461 [inline]
ip6_rcv_finish net/ipv6/ip6_input.c:79 [inline]
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ipv6_rcv+0x563/0x720 net/ipv6/ip6_input.c:310
__netif_receive_skb_one_core+0x115/0x180 net/core/dev.c:5527
__netif_receive_skb+0x1f/0x1b0 net/core/dev.c:5641
netif_receive_skb_internal net/core/dev.c:5727 [inline]
netif_receive_skb+0x133/0x700 net/core/dev.c:5786
tun_rx_batched+0x429/0x780 drivers/net/tun.c:1579
tun_get_user+0x29e7/0x3bc0 drivers/net/tun.c:2002
tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2048
call_write_iter include/linux/fs.h:1956 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x650/0xe40 fs/read_write.c:584
ksys_write+0x12f/0x250 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 2717b5adea9e ("net/tcp: Add tcp_hash_fail() ratelimited logs")
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Dmitry Safonov <dima@...sta.com>
Cc: Francesco Ruggeri <fruggeri@...sta.com>
Cc: David Ahern <dsahern@...nel.org>
---
 include/net/tcp_ao.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
index a375a171ef3cb37ab1d8246c72c6a3e83f5c9184..5daf96a3dbee14bd3786e19ea4972e351058e6e7 100644
--- a/include/net/tcp_ao.h
+++ b/include/net/tcp_ao.h
@@ -124,7 +124,7 @@ struct tcp_ao_info {
 #define tcp_hash_fail(msg, family, skb, fmt, ...)			\
 do {									\
 	const struct tcphdr *th = tcp_hdr(skb);				\
-	char hdr_flags[5] = {};						\
+	char hdr_flags[5];						\
 	char *f = hdr_flags;						\
 									\
 	if (th->fin)							\
@@ -135,8 +135,7 @@ do {									\
 		*f++ = 'R';						\
 	if (th->ack)							\
 		*f++ = 'A';						\
-	if (f != hdr_flags)						\
-		*f = ' ';						\
+	*f = 0;								\
 	if ((family) == AF_INET) {					\
 		net_info_ratelimited("%s for (%pI4, %d)->(%pI4, %d) %s" fmt "\n", \
 				msg, &ip_hdr(skb)->saddr, ntohs(th->source), \
-- 
2.42.0.820.g83a721a137-goog


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