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Date:   Tue, 24 Oct 2023 13:01:58 -0500
From:   George Kennedy <>
Subject: [PATCH v2] mlx5: fix init stage error handling to avoid double free of same QP and UAF

In the unlikely event that workqueue allocation fails and returns
NULL in mlx5_mkey_cache_init(), delete the call to
mlx5r_umr_resource_cleanup() (which frees the QP) in
mlx5_ib_stage_post_ib_reg_umr_init().  This will avoid attempted
double free of the same QP when __mlx5_ib_add() does its cleanup.

Syzkaller reported a UAF in ib_destroy_qp_user

workqueue: Failed to create a rescuer kthread for wq "mkey_cache": -EINTR
infiniband mlx5_0: mlx5_mkey_cache_init:981:(pid 1642):
failed to create work queue
infiniband mlx5_0: mlx5_ib_stage_post_ib_reg_umr_init:4075:(pid 1642):
mr cache init failed -12
BUG: KASAN: slab-use-after-free in ib_destroy_qp_user (drivers/infiniband/core/verbs.c:2073)
Read of size 8 at addr ffff88810da310a8 by task repro_upstream/1642

Call Trace:
kasan_report (mm/kasan/report.c:590)
ib_destroy_qp_user (drivers/infiniband/core/verbs.c:2073)
mlx5r_umr_resource_cleanup (drivers/infiniband/hw/mlx5/umr.c:198)
__mlx5_ib_add (drivers/infiniband/hw/mlx5/main.c:4178)
mlx5r_probe (drivers/infiniband/hw/mlx5/main.c:4402)

Allocated by task 1642:
__kmalloc (./include/linux/kasan.h:198 mm/slab_common.c:1026
create_qp (./include/linux/slab.h:603 ./include/linux/slab.h:720
./include/rdma/ib_verbs.h:2795 drivers/infiniband/core/verbs.c:1209)
ib_create_qp_kernel (drivers/infiniband/core/verbs.c:1347)
mlx5r_umr_resource_init (drivers/infiniband/hw/mlx5/umr.c:164)
mlx5_ib_stage_post_ib_reg_umr_init (drivers/infiniband/hw/mlx5/main.c:4070)
__mlx5_ib_add (drivers/infiniband/hw/mlx5/main.c:4168)
mlx5r_probe (drivers/infiniband/hw/mlx5/main.c:4402)

Freed by task 1642:
__kmem_cache_free (mm/slub.c:1826 mm/slub.c:3809 mm/slub.c:3822)
ib_destroy_qp_user (drivers/infiniband/core/verbs.c:2112)
mlx5r_umr_resource_cleanup (drivers/infiniband/hw/mlx5/umr.c:198)
mlx5_ib_stage_post_ib_reg_umr_init (drivers/infiniband/hw/mlx5/main.c:4076
__mlx5_ib_add (drivers/infiniband/hw/mlx5/main.c:4168)
mlx5r_probe (drivers/infiniband/hw/mlx5/main.c:4402)

The buggy address belongs to the object at ffff88810da31000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 168 bytes inside of
freed 2048-byte region [ffff88810da31000, ffff88810da31800)

The buggy address belongs to the physical page:
page:000000003b5e469d refcount:1 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x10da30
head:000000003b5e469d order:3 entire_mapcount:0 nr_pages_mapped:0
flags: 0x17ffffc0000840(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
page_type: 0xffffffff()
raw: 0017ffffc0000840 ffff888100042f00 ffffea0004180800 dead000000000002
raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88810da30f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88810da31000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88810da31080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810da31100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810da31180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
Disabling lock debugging due to kernel taint

Fixes: 04876c12c19e ("RDMA/mlx5: Move init and cleanup of UMR to umr.c")
Reported-by: syzkaller <>
Suggested-by: Leon Romanovsky <>
Signed-off-by: George Kennedy <>
v2: went with fix suggested by: Leon Romanovsky <>

 drivers/infiniband/hw/mlx5/main.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index 555629b7..5d963ab 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -4071,10 +4071,8 @@ static int mlx5_ib_stage_post_ib_reg_umr_init(struct mlx5_ib_dev *dev)
 		return ret;
 	ret = mlx5_mkey_cache_init(dev);
-	if (ret) {
+	if (ret)
 		mlx5_ib_warn(dev, "mr cache init failed %d\n", ret);
-		mlx5r_umr_resource_cleanup(dev);
-	}
 	return ret;

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