2021-09-23 09:10:44

by 王贇

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

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 <[email protected]>
Signed-off-by: Michael Wang <[email protected]>
---
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

2021-09-24 02:39:38

by 王贇

Subject: [PATCH v2] net: prevent user from passing illegal stab size

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 protected]>
Signed-off-by: Michael Wang <[email protected]>
---
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 6d7b12c..bf79f3a 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 5e90e9b..12f39a2 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);
--
1.8.3.1