When I debug a kernel crash issue in funcitonfs, found ffs_data.ref overflowed, While functionfs is unmounting, ffs_data is put twice.

Commit 43938613c6fd ("drivers, usb: convert ffs_data.ref from atomic_t to refcount_t") can avoid refcount overflow, but that is risk some situations. So no need put ffs data in ffs_fs_kill_sb, already put in ffs_data_closed.

The issue can be reproduced in Mediatek mt6763 SoC, ffs for ADB device. KASAN enabled configuration reports use-after-free errro.

BUG: KASAN: use-after-free in refcount_dec_and_test+0x14/0xe0 at addr ffffffc0579386a0 Read of size 4 by task umount/4650 ==================================================== BUG kmalloc-512 (Tainted: P W O ): kasan: bad access detected -----------------------------------------------------------------------------

INFO: Allocated in ffs_fs_mount+0x194/0x844 age=22856 cpu=2 pid=566 alloc_debug_processing+0x1ac/0x1e8 ___slab_alloc.constprop.63+0x640/0x648 __slab_alloc.isra.57.constprop.62+0x24/0x34 kmem_cache_alloc_trace+0x1a8/0x2bc ffs_fs_mount+0x194/0x844 mount_fs+0x6c/0x1d0 vfs_kern_mount+0x50/0x1b4 do_mount+0x258/0x1034 INFO: Freed in ffs_data_put+0x25c/0x320 age=0 cpu=3 pid=4650 free_debug_processing+0x22c/0x434 __slab_free+0x2d8/0x3a0 kfree+0x254/0x264 ffs_data_put+0x25c/0x320 ffs_data_closed+0x124/0x15c ffs_fs_kill_sb+0xb8/0x110 deactivate_locked_super+0x6c/0x98 deactivate_super+0xb0/0xbc INFO: Object 0xffffffc057938600 @offset=1536 fp=0x (null) ...... Call trace: [<ffffff900808cf5c>] dump_backtrace+0x0/0x250 [<ffffff900808d3a0>] show_stack+0x14/0x1c [<ffffff90084a8c04>] dump_stack+0xa0/0xc8 [<ffffff900826c2b4>] print_trailer+0x158/0x260 [<ffffff900826d9d8>] object_err+0x3c/0x40 [<ffffff90082745f0>] kasan_report_error+0x2a8/0x754 [<ffffff9008274f84>] kasan_report+0x5c/0x60 [<ffffff9008273208>] __asan_load4+0x70/0x88 [<ffffff90084cd81c>] refcount_dec_and_test+0x14/0xe0 [<ffffff9008d98f9c>] ffs_data_put+0x80/0x320 [<ffffff9008d9d904>] ffs_fs_kill_sb+0xc8/0x110 [<ffffff90082852a0>] deactivate_locked_super+0x6c/0x98 [<ffffff900828537c>] deactivate_super+0xb0/0xbc [<ffffff90082af0c0>] cleanup_mnt+0x64/0xec [<ffffff90082af1b0>] __cleanup_mnt+0x10/0x18 [<ffffff90080d9e68>] task_work_run+0xcc/0x124 [<ffffff900808c8c0>] do_notify_resume+0x60/0x70 [<ffffff90080866e4>] work_pending+0x10/0x14

Cc: stable@vger.kernel.org Signed-off-by: Xinyong xinyong.fang@linux.alibaba.com --- drivers/usb/gadget/function/f_fs.c | 1 - 1 file changed, 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index c2592d8..d2428a9 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -1538,7 +1538,6 @@ static int ffs_fs_parse_opts(struct ffs_sb_fill_data *data, char *opts) if (sb->s_fs_info) { ffs_release_dev(sb->s_fs_info); ffs_data_closed(sb->s_fs_info); - ffs_data_put(sb->s_fs_info); } }