6.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Johannes Thumshirn johannes.thumshirn@wdc.com
commit 1ec17ef59168a1a6f1105f5dc517f783839a5302 upstream.
Shinichiro reported the following use-after-free triggered by the device replace operation in fstests btrfs/070.
BTRFS info (device nullb1): scrub: finished on devid 1 with status: 0 ================================================================== BUG: KASAN: slab-use-after-free in do_zone_finish+0x91a/0xb90 [btrfs] Read of size 8 at addr ffff8881543c8060 by task btrfs-cleaner/3494007
CPU: 0 PID: 3494007 Comm: btrfs-cleaner Tainted: G W 6.8.0-rc5-kts #1 Hardware name: Supermicro Super Server/X11SPi-TF, BIOS 3.3 02/21/2020 Call Trace: <TASK> dump_stack_lvl+0x5b/0x90 print_report+0xcf/0x670 ? __virt_addr_valid+0x200/0x3e0 kasan_report+0xd8/0x110 ? do_zone_finish+0x91a/0xb90 [btrfs] ? do_zone_finish+0x91a/0xb90 [btrfs] do_zone_finish+0x91a/0xb90 [btrfs] btrfs_delete_unused_bgs+0x5e1/0x1750 [btrfs] ? __pfx_btrfs_delete_unused_bgs+0x10/0x10 [btrfs] ? btrfs_put_root+0x2d/0x220 [btrfs] ? btrfs_clean_one_deleted_snapshot+0x299/0x430 [btrfs] cleaner_kthread+0x21e/0x380 [btrfs] ? __pfx_cleaner_kthread+0x10/0x10 [btrfs] kthread+0x2e3/0x3c0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x31/0x70 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1b/0x30 </TASK>
Allocated by task 3493983: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 btrfs_alloc_device+0xb3/0x4e0 [btrfs] device_list_add.constprop.0+0x993/0x1630 [btrfs] btrfs_scan_one_device+0x219/0x3d0 [btrfs] btrfs_control_ioctl+0x26e/0x310 [btrfs] __x64_sys_ioctl+0x134/0x1b0 do_syscall_64+0x99/0x190 entry_SYSCALL_64_after_hwframe+0x6e/0x76
Freed by task 3494056: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3f/0x60 poison_slab_object+0x102/0x170 __kasan_slab_free+0x32/0x70 kfree+0x11b/0x320 btrfs_rm_dev_replace_free_srcdev+0xca/0x280 [btrfs] btrfs_dev_replace_finishing+0xd7e/0x14f0 [btrfs] btrfs_dev_replace_by_ioctl+0x1286/0x25a0 [btrfs] btrfs_ioctl+0xb27/0x57d0 [btrfs] __x64_sys_ioctl+0x134/0x1b0 do_syscall_64+0x99/0x190 entry_SYSCALL_64_after_hwframe+0x6e/0x76
The buggy address belongs to the object at ffff8881543c8000 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 96 bytes inside of freed 1024-byte region [ffff8881543c8000, ffff8881543c8400)
The buggy address belongs to the physical page: page:00000000fe2c1285 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1543c8 head:00000000fe2c1285 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0 flags: 0x17ffffc0000840(slab|head|node=0|zone=2|lastcpupid=0x1fffff) page_type: 0xffffffff() raw: 0017ffffc0000840 ffff888100042dc0 ffffea0019e8f200 dead000000000002 raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: ffff8881543c7f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff8881543c7f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8881543c8000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^ ffff8881543c8080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881543c8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
This UAF happens because we're accessing stale zone information of a already removed btrfs_device in do_zone_finish().
The sequence of events is as follows:
btrfs_dev_replace_start btrfs_scrub_dev btrfs_dev_replace_finishing btrfs_dev_replace_update_device_in_mapping_tree <-- devices replaced btrfs_rm_dev_replace_free_srcdev btrfs_free_device <-- device freed
cleaner_kthread btrfs_delete_unused_bgs btrfs_zone_finish do_zone_finish <-- refers the freed device
The reason for this is that we're using a cached pointer to the chunk_map from the block group, but on device replace this cached pointer can contain stale device entries.
The staleness comes from the fact, that btrfs_block_group::physical_map is not a pointer to a btrfs_chunk_map but a memory copy of it.
Also take the fs_info::dev_replace::rwsem to prevent btrfs_dev_replace_update_device_in_mapping_tree() from changing the device underneath us again.
Note: btrfs_dev_replace_update_device_in_mapping_tree() is holding fs_info::mapping_tree_lock, but as this is a spinning read/write lock we cannot take it as the call to blkdev_zone_mgmt() requires a memory allocation which may not sleep. But btrfs_dev_replace_update_device_in_mapping_tree() is always called with the fs_info::dev_replace::rwsem held in write mode.
Many thanks to Shinichiro for analyzing the bug.
Reported-by: Shinichiro Kawasaki shinichiro.kawasaki@wdc.com CC: stable@vger.kernel.org # 6.8 Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Johannes Thumshirn johannes.thumshirn@wdc.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/zoned.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
--- a/fs/btrfs/zoned.c +++ b/fs/btrfs/zoned.c @@ -1563,11 +1563,7 @@ int btrfs_load_block_group_zone_info(str if (!map) return -EINVAL;
- cache->physical_map = btrfs_clone_chunk_map(map, GFP_NOFS); - if (!cache->physical_map) { - ret = -ENOMEM; - goto out; - } + cache->physical_map = map;
zone_info = kcalloc(map->num_stripes, sizeof(*zone_info), GFP_NOFS); if (!zone_info) { @@ -1679,7 +1675,6 @@ out: } bitmap_free(active); kfree(zone_info); - btrfs_free_chunk_map(map);
return ret; } @@ -2164,6 +2159,7 @@ static int do_zone_finish(struct btrfs_b struct btrfs_chunk_map *map; const bool is_metadata = (block_group->flags & (BTRFS_BLOCK_GROUP_METADATA | BTRFS_BLOCK_GROUP_SYSTEM)); + struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace; int ret = 0; int i;
@@ -2239,6 +2235,7 @@ static int do_zone_finish(struct btrfs_b btrfs_clear_data_reloc_bg(block_group); spin_unlock(&block_group->lock);
+ down_read(&dev_replace->rwsem); map = block_group->physical_map; for (i = 0; i < map->num_stripes; i++) { struct btrfs_device *device = map->stripes[i].dev; @@ -2253,13 +2250,16 @@ static int do_zone_finish(struct btrfs_b zinfo->zone_size >> SECTOR_SHIFT, GFP_NOFS);
- if (ret) + if (ret) { + up_read(&dev_replace->rwsem); return ret; + }
if (!(block_group->flags & BTRFS_BLOCK_GROUP_DATA)) zinfo->reserved_active_zones++; btrfs_dev_clear_active_zone(device, physical); } + up_read(&dev_replace->rwsem);
if (!fully_written) btrfs_dec_block_group_ro(block_group);