Subject: [PATCH AUTOSEL 5.14 25/40] net: prevent user from passing illegal stab size

From: Sasha Levin <[email-masked]>
Date: Tue, 5 Oct 2021 09:50:04 -0400

From: 王贇 <[email-masked]>

[ Upstream commit b193e15ac69d56f35e1d8e2b5d16cbd47764d053 ]

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 log value passing from
user, and will use the insane value later to calculate pkt_len.

This patch just add a check on the size/cell_log to avoid insane
calculation.

Reported-by: Abaci <[email-masked]>
Signed-off-by: Michael Wang <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---
 include/net/pkt_sched.h | 1 +
 net/sched/sch_api.c     | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 6d7b12cba015..bf79f3a890af 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -11,6 +11,7 @@
 #include <uapi/linux/pkt_sched.h>
 
 #define DEFAULT_TX_QUEUE_LEN	1000
+#define STAB_SIZE_LOG_MAX	30
 
 struct qdisc_walker {
 	int	stop;
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index f87d07736a14..148edd0e71e3 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -513,6 +513,12 @@ static struct qdisc_size_table *qdisc_get_stab(struct nlattr *opt,
 		return stab;
 	}
 
+	if (s->size_log > STAB_SIZE_LOG_MAX ||
+	    s->cell_log > STAB_SIZE_LOG_MAX) {
+		NL_SET_ERR_MSG(extack, "Invalid logarithmic size of size table");
+		return ERR_PTR(-EINVAL);
+	}
+
 	stab = kmalloc(sizeof(*stab) + tsize * sizeof(u16), GFP_KERNEL);
 	if (!stab)
 		return ERR_PTR(-ENOMEM);
-- 
2.33.0