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Subject[PATCH 5.15 150/262] blktrace: fix use after free for struct blk_trace
Date
From: Yu Kuai <yukuai3@huawei.com>

commit 30939293262eb433c960c4532a0d59c4073b2b84 upstream.

When tracing the whole disk, 'dropped' and 'msg' will be created
under 'q->debugfs_dir' and 'bt->dir' is NULL, thus blk_trace_free()
won't remove those files. What's worse, the following UAF can be
triggered because of accessing stale 'dropped' and 'msg':

==================================================================
BUG: KASAN: use-after-free in blk_dropped_read+0x89/0x100
Read of size 4 at addr ffff88816912f3d8 by task blktrace/1188

CPU: 27 PID: 1188 Comm: blktrace Not tainted 5.17.0-rc4-next-20220217+ #469
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-4
Call Trace:
<TASK>
dump_stack_lvl+0x34/0x44
print_address_description.constprop.0.cold+0xab/0x381
? blk_dropped_read+0x89/0x100
? blk_dropped_read+0x89/0x100
kasan_report.cold+0x83/0xdf
? blk_dropped_read+0x89/0x100
kasan_check_range+0x140/0x1b0
blk_dropped_read+0x89/0x100
? blk_create_buf_file_callback+0x20/0x20
? kmem_cache_free+0xa1/0x500
? do_sys_openat2+0x258/0x460
full_proxy_read+0x8f/0xc0
vfs_read+0xc6/0x260
ksys_read+0xb9/0x150
? vfs_write+0x3d0/0x3d0
? fpregs_assert_state_consistent+0x55/0x60
? exit_to_user_mode_prepare+0x39/0x1e0
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fbc080d92fd
Code: ce 20 00 00 75 10 b8 00 00 00 00 0f 05 48 3d 01 f0 ff ff 73 31 c3 48 83 1
RSP: 002b:00007fbb95ff9cb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007fbb95ff9dc0 RCX: 00007fbc080d92fd
RDX: 0000000000000100 RSI: 00007fbb95ff9cc0 RDI: 0000000000000045
RBP: 0000000000000045 R08: 0000000000406299 R09: 00000000fffffffd
R10: 000000000153afa0 R11: 0000000000000293 R12: 00007fbb780008c0
R13: 00007fbb78000938 R14: 0000000000608b30 R15: 00007fbb780029c8
</TASK>

Allocated by task 1050:
kasan_save_stack+0x1e/0x40
__kasan_kmalloc+0x81/0xa0
do_blk_trace_setup+0xcb/0x410
__blk_trace_setup+0xac/0x130
blk_trace_ioctl+0xe9/0x1c0
blkdev_ioctl+0xf1/0x390
__x64_sys_ioctl+0xa5/0xe0
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 1050:
kasan_save_stack+0x1e/0x40
kasan_set_track+0x21/0x30
kasan_set_free_info+0x20/0x30
__kasan_slab_free+0x103/0x180
kfree+0x9a/0x4c0
__blk_trace_remove+0x53/0x70
blk_trace_ioctl+0x199/0x1c0
blkdev_common_ioctl+0x5e9/0xb30
blkdev_ioctl+0x1a5/0x390
__x64_sys_ioctl+0xa5/0xe0
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff88816912f380
which belongs to the cache kmalloc-96 of size 96
The buggy address is located 88 bytes inside of
96-byte region [ffff88816912f380, ffff88816912f3e0)
The buggy address belongs to the page:
page:000000009a1b4e7c refcount:1 mapcount:0 mapping:0000000000000000 index:0x0f
flags: 0x17ffffc0000200(slab|node=0|zone=2|lastcpupid=0x1fffff)
raw: 0017ffffc0000200 ffffea00044f1100 dead000000000002 ffff88810004c780
raw: 0000000000000000 0000000000200020 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88816912f280: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
ffff88816912f300: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>ffff88816912f380: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
^
ffff88816912f400: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
ffff88816912f480: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
==================================================================

Fixes: c0ea57608b69 ("blktrace: remove debugfs file dentries from struct blk_trace")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220228034354.4047385-1-yukuai3@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/blktrace.c | 26 ++++++++++++++++++--------
1 file changed, 18 insertions(+), 8 deletions(-)

--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -310,10 +310,20 @@ record_it:
local_irq_restore(flags);
}

-static void blk_trace_free(struct blk_trace *bt)
+static void blk_trace_free(struct request_queue *q, struct blk_trace *bt)
{
relay_close(bt->rchan);
- debugfs_remove(bt->dir);
+
+ /*
+ * If 'bt->dir' is not set, then both 'dropped' and 'msg' are created
+ * under 'q->debugfs_dir', thus lookup and remove them.
+ */
+ if (!bt->dir) {
+ debugfs_remove(debugfs_lookup("dropped", q->debugfs_dir));
+ debugfs_remove(debugfs_lookup("msg", q->debugfs_dir));
+ } else {
+ debugfs_remove(bt->dir);
+ }
free_percpu(bt->sequence);
free_percpu(bt->msg_data);
kfree(bt);
@@ -335,10 +345,10 @@ static void put_probe_ref(void)
mutex_unlock(&blk_probe_mutex);
}

-static void blk_trace_cleanup(struct blk_trace *bt)
+static void blk_trace_cleanup(struct request_queue *q, struct blk_trace *bt)
{
synchronize_rcu();
- blk_trace_free(bt);
+ blk_trace_free(q, bt);
put_probe_ref();
}

@@ -352,7 +362,7 @@ static int __blk_trace_remove(struct req
return -EINVAL;

if (bt->trace_state != Blktrace_running)
- blk_trace_cleanup(bt);
+ blk_trace_cleanup(q, bt);

return 0;
}
@@ -572,7 +582,7 @@ static int do_blk_trace_setup(struct req
ret = 0;
err:
if (ret)
- blk_trace_free(bt);
+ blk_trace_free(q, bt);
return ret;
}

@@ -1615,7 +1625,7 @@ static int blk_trace_remove_queue(struct

put_probe_ref();
synchronize_rcu();
- blk_trace_free(bt);
+ blk_trace_free(q, bt);
return 0;
}

@@ -1646,7 +1656,7 @@ static int blk_trace_setup_queue(struct
return 0;

free_bt:
- blk_trace_free(bt);
+ blk_trace_free(q, bt);
return ret;
}


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