[PATCH] net: prevent user from passing illegal stab size

[王贇]

We observed below report when playing with netlink sock:

  UBSAN: shift-out-of-bounds in net/sched/sch_api.c:580:10
  shift exponent 249 is too large for 32-bit type
  CPU: 0 PID: 685 Comm: a.out Not tainted
  Call Trace:
   dump_stack_lvl+0x8d/0xcf
   ubsan_epilogue+0xa/0x4e
   __ubsan_handle_shift_out_of_bounds+0x161/0x182
   __qdisc_calculate_pkt_len+0xf0/0x190
   __dev_queue_xmit+0x2ed/0x15b0

it seems like kernel won't check the stab size_log passing from
user, and will use the insane value later to calculate pkt_len.

This patch just add a check on the size_log to avoid insane
calculation.

Reported-by: Abaci <abaci@xxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Wang <yun.wang@xxxxxxxxxxxxxxxxx>
---
 include/uapi/linux/pkt_sched.h | 1 +
 net/sched/sch_api.c            | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index ec88590..fa194a0 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -98,6 +98,7 @@ struct tc_ratespec {
 };

 #define TC_RTAB_SIZE	1024
+#define TC_LOG_MAX	30

 struct tc_sizespec {
 	unsigned char	cell_log;
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 5e90e9b..1b6b8f8 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -513,6 +513,9 @@ static struct qdisc_size_table *qdisc_get_stab(struct nlattr *opt,
 		return stab;
 	}

+	if (s->size_log > TC_LOG_MAX)
+		return ERR_PTR(-EINVAL);
+
 	stab = kmalloc(sizeof(*stab) + tsize * sizeof(u16), GFP_KERNEL);
 	if (!stab)
 		return ERR_PTR(-ENOMEM);
-- 
1.8.3.1