[PATCH 4.14 14/33] net_sched: fix NULL deref in fifo_set_limit()

Greg Kroah-Hartman
2021-10-14T14:57:57Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 560ee196fe9e5037e5015e2cdb14b3aecb1cd7dc ]

syzbot reported another NULL deref in fifo_set_limit() [1]

I could repro the issue with :

unshare -n
tc qd add dev lo root handle 1:0 tbf limit 200000 burst 70000 rate 100Mbit
tc qd replace dev lo parent 1:0 pfifo_fast
tc qd change dev lo root handle 1:0 tbf limit 300000 burst 70000 rate 100Mbit

pfifo_fast does not have a change() operation.
Make fifo_set_limit() more robust about this.

[1]
BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 1cf99067 P4D 1cf99067 PUD 7ca49067 PMD 0
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 14443 Comm: syz-executor959 Not tainted 5.15.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc9000e2f7310 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffffffff8d6ecc00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff888024c27910 RDI: ffff888071e34000
RBP: ffff888071e34000 R08: 0000000000000001 R09: ffffffff8fcfb947
R10: 0000000000000001 R11: 0000000000000000 R12: ffff888024c27910
R13: ffff888071e34018 R14: 0000000000000000 R15: ffff88801ef74800
FS: 00007f321d897700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000722c3000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
fifo_set_limit net/sched/sch_fifo.c:242 [inline]
fifo_set_limit+0x198/0x210 net/sched/sch_fifo.c:227
tbf_change+0x6ec/0x16d0 net/sched/sch_tbf.c:418
qdisc_change net/sched/sch_api.c:1332 [inline]
tc_modify_qdisc+0xd9a/0x1a60 net/sched/sch_api.c:1634
rtnetlink_rcv_msg+0x413/0xb80 net/core/rtnetlink.c:5572
netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504
netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1340
netlink_sendmsg+0x86d/0xdb0 net/netlink/af_netlink.c:1929
sock_sendmsg_nosec net/socket.c:704 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:724
____sys_sendmsg+0x6e8/0x810 net/socket.c:2409
___sys_sendmsg+0xf3/0x170 net/socket.c:2463
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2492
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

Fixes: fb0305ce1b03 ("net-sched: consolidate default fifo qdisc setup")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Link: https://lore.kernel.org/r/20210930212239.3430364-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/sch_fifo.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/sched/sch_fifo.c b/net/sched/sch_fifo.c
index 1e37247656f8..8b7110cbcce4 100644
--- a/net/sched/sch_fifo.c
+++ b/net/sched/sch_fifo.c
@@ -151,6 +151,9 @@ int fifo_set_limit(struct Qdisc *q, unsigned int limit)
if (strncmp(q->ops->id + 1, "fifo", 4) != 0)
return 0;

+ if (!q->ops->change)
+ return 0;
+
nla = kmalloc(nla_attr_size(sizeof(struct tc_fifo_qopt)), GFP_KERNEL);
if (nla) {
nla->nla_type = RTM_NEWQDISC;
--
2.33.0