[PATCH 5.4 149/215] net/sched: act_skbmod: prevent kernel-infoleak

Greg Kroah-Hartman
2024-04-11T10:22:10Z

From: Eric Dumazet <edumazet@google.com>

commit d313eb8b77557a6d5855f42d2234bd592c7b50dd upstream.

syzbot found that tcf_skbmod_dump() was copying four bytes
from kernel stack to user space [1].

The issue here is that 'struct tc_skbmod' has a four bytes hole.

We need to clear the structure before filling fields.

[1]
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
BUG: KMSAN: kernel-infoleak in copy_to_user_iter lib/iov_iter.c:24 [inline]
BUG: KMSAN: kernel-infoleak in iterate_ubuf include/linux/iov_iter.h:29 [inline]
BUG: KMSAN: kernel-infoleak in iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
BUG: KMSAN: kernel-infoleak in iterate_and_advance include/linux/iov_iter.h:271 [inline]
BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x366/0x2520 lib/iov_iter.c:185
instrument_copy_to_user include/linux/instrumented.h:114 [inline]
copy_to_user_iter lib/iov_iter.c:24 [inline]
iterate_ubuf include/linux/iov_iter.h:29 [inline]
iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
iterate_and_advance include/linux/iov_iter.h:271 [inline]
_copy_to_iter+0x366/0x2520 lib/iov_iter.c:185
copy_to_iter include/linux/uio.h:196 [inline]
simple_copy_to_iter net/core/datagram.c:532 [inline]
__skb_datagram_iter+0x185/0x1000 net/core/datagram.c:420
skb_copy_datagram_iter+0x5c/0x200 net/core/datagram.c:546
skb_copy_datagram_msg include/linux/skbuff.h:4050 [inline]
netlink_recvmsg+0x432/0x1610 net/netlink/af_netlink.c:1962
sock_recvmsg_nosec net/socket.c:1046 [inline]
sock_recvmsg+0x2c4/0x340 net/socket.c:1068
__sys_recvfrom+0x35a/0x5f0 net/socket.c:2242
__do_sys_recvfrom net/socket.c:2260 [inline]
__se_sys_recvfrom net/socket.c:2256 [inline]
__x64_sys_recvfrom+0x126/0x1d0 net/socket.c:2256
do_syscall_64+0xd5/0x1f0
entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was stored to memory at:
pskb_expand_head+0x30f/0x19d0 net/core/skbuff.c:2253
netlink_trim+0x2c2/0x330 net/netlink/af_netlink.c:1317
netlink_unicast+0x9f/0x1260 net/netlink/af_netlink.c:1351
nlmsg_unicast include/net/netlink.h:1144 [inline]
nlmsg_notify+0x21d/0x2f0 net/netlink/af_netlink.c:2610
rtnetlink_send+0x73/0x90 net/core/rtnetlink.c:741
rtnetlink_maybe_send include/linux/rtnetlink.h:17 [inline]
tcf_add_notify net/sched/act_api.c:2048 [inline]
tcf_action_add net/sched/act_api.c:2071 [inline]
tc_ctl_action+0x146e/0x19d0 net/sched/act_api.c:2119
rtnetlink_rcv_msg+0x1737/0x1900 net/core/rtnetlink.c:6595
netlink_rcv_skb+0x375/0x650 net/netlink/af_netlink.c:2559
rtnetlink_rcv+0x34/0x40 net/core/rtnetlink.c:6613
netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
netlink_unicast+0xf4c/0x1260 net/netlink/af_netlink.c:1361
netlink_sendmsg+0x10df/0x11f0 net/netlink/af_netlink.c:1905
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x30f/0x380 net/socket.c:745
____sys_sendmsg+0x877/0xb60 net/socket.c:2584
___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
__sys_sendmsg net/socket.c:2667 [inline]
__do_sys_sendmsg net/socket.c:2676 [inline]
__se_sys_sendmsg net/socket.c:2674 [inline]
__x64_sys_sendmsg+0x307/0x4a0 net/socket.c:2674
do_syscall_64+0xd5/0x1f0
entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was stored to memory at:
__nla_put lib/nlattr.c:1041 [inline]
nla_put+0x1c6/0x230 lib/nlattr.c:1099
tcf_skbmod_dump+0x23f/0xc20 net/sched/act_skbmod.c:256
tcf_action_dump_old net/sched/act_api.c:1191 [inline]
tcf_action_dump_1+0x85e/0x970 net/sched/act_api.c:1227
tcf_action_dump+0x1fd/0x460 net/sched/act_api.c:1251
tca_get_fill+0x519/0x7a0 net/sched/act_api.c:1628
tcf_add_notify_msg net/sched/act_api.c:2023 [inline]
tcf_add_notify net/sched/act_api.c:2042 [inline]
tcf_action_add net/sched/act_api.c:2071 [inline]
tc_ctl_action+0x1365/0x19d0 net/sched/act_api.c:2119
rtnetlink_rcv_msg+0x1737/0x1900 net/core/rtnetlink.c:6595
netlink_rcv_skb+0x375/0x650 net/netlink/af_netlink.c:2559
rtnetlink_rcv+0x34/0x40 net/core/rtnetlink.c:6613
netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
netlink_unicast+0xf4c/0x1260 net/netlink/af_netlink.c:1361
netlink_sendmsg+0x10df/0x11f0 net/netlink/af_netlink.c:1905
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x30f/0x380 net/socket.c:745
____sys_sendmsg+0x877/0xb60 net/socket.c:2584
___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
__sys_sendmsg net/socket.c:2667 [inline]
__do_sys_sendmsg net/socket.c:2676 [inline]
__se_sys_sendmsg net/socket.c:2674 [inline]
__x64_sys_sendmsg+0x307/0x4a0 net/socket.c:2674
do_syscall_64+0xd5/0x1f0
entry_SYSCALL_64_after_hwframe+0x6d/0x75

Local variable opt created at:
tcf_skbmod_dump+0x9d/0xc20 net/sched/act_skbmod.c:244
tcf_action_dump_old net/sched/act_api.c:1191 [inline]
tcf_action_dump_1+0x85e/0x970 net/sched/act_api.c:1227

Bytes 188-191 of 248 are uninitialized
Memory access of size 248 starts at ffff888117697680
Data copied to user address 00007ffe56d855f0

Fixes: 86da71b57383 ("net_sched: Introduce skbmod action")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20240403130908.93421-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/act_skbmod.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/net/sched/act_skbmod.c
+++ b/net/sched/act_skbmod.c
@@ -219,13 +219,13 @@ static int tcf_skbmod_dump(struct sk_buf
struct tcf_skbmod *d = to_skbmod(a);
unsigned char *b = skb_tail_pointer(skb);
struct tcf_skbmod_params *p;
- struct tc_skbmod opt = {
- .index = d->tcf_index,
- .refcnt = refcount_read(&d->tcf_refcnt) - ref,
- .bindcnt = atomic_read(&d->tcf_bindcnt) - bind,
- };
+ struct tc_skbmod opt;
struct tcf_t t;

+ memset(&opt, 0, sizeof(opt));
+ opt.index = d->tcf_index;
+ opt.refcnt = refcount_read(&d->tcf_refcnt) - ref,
+ opt.bindcnt = atomic_read(&d->tcf_bindcnt) - bind;
spin_lock_bh(&d->tcf_lock);
opt.action = d->tcf_action;
p = rcu_dereference_protected(d->skbmod_p,