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If a later step fails, error_sysfs removes the device with list_del_rcu() and then frees it without waiting for an RCU grace period. A concurrent reader such as btrfs_ioctl_dev_info() may still hold the device pointer it obtained under rcu_read_lock() and dereference it after btrfs_free_device() has already freed it, triggering a KASAN slab-use-after-free report: BUG: KASAN: slab-use-after-free in btrfs_ioctl+0x58e4/0x5d40 Read of size 8 at addr ffff8881176fa870 by task poc/84 Call Trace: kasan_report+0xe4/0x1a0 btrfs_ioctl+0x58e4/0x5d40 __x64_sys_ioctl+0x121/0x1a0 do_syscall_64+0xf7/0x5a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f Allocated by task 81: btrfs_alloc_device+0xb0/0x3e0 btrfs_init_new_device+0x4b2/0x3660 btrfs_ioctl_add_dev+0x179/0x430 btrfs_ioctl+0x11e0/0x5d40 Freed by task 81: kfree+0x1b8/0x550 btrfs_init_new_device+0x56b/0x3660 btrfs_ioctl_add_dev+0x179/0x430 btrfs_ioctl+0x11e0/0x5d40 Wait for an RCU grace period after removing the device from the list and before freeing it. Fixes: 39379faaad79 ("btrfs: revert fs_devices state on error of btrfs_init_new_device") Assisted-by: Codex:gpt-5.6 Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Mai Hai Son --- fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 9b66eb584..af59291b7 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -3133,6 +3133,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path btrfs_update_per_profile_avail(fs_info); mutex_unlock(&fs_info->chunk_mutex); mutex_unlock(&fs_info->fs_devices->device_list_mutex); + synchronize_rcu(); error_trans: if (trans) btrfs_end_transaction(trans); base-commit: 4d7d9486c04d917265f64c55bd23b2cc4fe7749c