[PATCH 4.9 149/207] llc: fix out-of-bound array index in llc_sk_dev_hash()

Greg Kroah-Hartman
2021-11-24T12:24:08Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 8ac9dfd58b138f7e82098a4e0a0d46858b12215b ]

Both ifindex and LLC_SK_DEV_HASH_ENTRIES are signed.

This means that (ifindex % LLC_SK_DEV_HASH_ENTRIES) is negative
if @ifindex is negative.

We could simply make LLC_SK_DEV_HASH_ENTRIES unsigned.

In this patch I chose to use hash_32() to get more entropy
from @ifindex, like llc_sk_laddr_hashfn().

UBSAN: array-index-out-of-bounds in ./include/net/llc.h:75:26
index -43 is out of range for type 'hlist_head [64]'
CPU: 1 PID: 20999 Comm: syz-executor.3 Not tainted 5.15.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
ubsan_epilogue+0xb/0x5a lib/ubsan.c:151
__ubsan_handle_out_of_bounds.cold+0x62/0x6c lib/ubsan.c:291
llc_sk_dev_hash include/net/llc.h:75 [inline]
llc_sap_add_socket+0x49c/0x520 net/llc/llc_conn.c:697
llc_ui_bind+0x680/0xd70 net/llc/af_llc.c:404
__sys_bind+0x1e9/0x250 net/socket.c:1693
__do_sys_bind net/socket.c:1704 [inline]
__se_sys_bind net/socket.c:1702 [inline]
__x64_sys_bind+0x6f/0xb0 net/socket.c:1702
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fa503407ae9

Fixes: 6d2e3ea28446 ("llc: use a device based hash table to speed up multicast delivery")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/llc.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/net/llc.h b/include/net/llc.h
index 95e5ced4c1339..18dfd3e49a69f 100644
--- a/include/net/llc.h
+++ b/include/net/llc.h
@@ -72,7 +72,9 @@ struct llc_sap {
static inline
struct hlist_head *llc_sk_dev_hash(struct llc_sap *sap, int ifindex)
{
- return &sap->sk_dev_hash[ifindex % LLC_SK_DEV_HASH_ENTRIES];
+ u32 bucket = hash_32(ifindex, LLC_SK_DEV_HASH_BITS);
+
+ return &sap->sk_dev_hash[bucket];
}

static inline
--
2.33.0