On Sat, Feb 26, 2022 at 05:53:43PM +0800, Yu Kuai wrote:
> This reverts commit c0ea57608b691d6cde8aff23e11f9858a86b5918.
>
> 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 stale 'dropped' and 'msg':
Only root has access to these files, right?
>
> ==================================================================
> 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@xxxxxxxxxx>
> ---
> include/linux/blktrace_api.h | 2 ++
> kernel/trace/blktrace.c | 8 ++++++--
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h
> index 22501a293fa5..f288d229727c 100644
> --- a/include/linux/blktrace_api.h
> +++ b/include/linux/blktrace_api.h
> @@ -23,6 +23,8 @@ struct blk_trace {
> u32 pid;
> u32 dev;
> struct dentry *dir;
> + struct dentry *dropped_file;
> + struct dentry *msg_file;
No need to save these dentries. Just look them up when you want to
remove the files.
> struct list_head running_list;
> atomic_t dropped;
> };
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 19514edc44f7..13152a17fdb3 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -312,6 +312,8 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
>
> static void blk_trace_free(struct blk_trace *bt)
> {
> + debugfs_remove(bt->msg_file);
> + debugfs_remove(bt->dropped_file);
> relay_close(bt->rchan);
> debugfs_remove(bt->dir);
Why not just move this line up above relay_close()?
Then you the whole directory is properly removed, along with the files
in it.
So this can just be a 1 line change :)
thanks,
greg k-h
