Created attachment 276197 [details] The (compressed) crafted image which causes crash - Overview use-after-free in try_merge_free_space() when mounting a crafted btrfs image - Reproduce (4.17 KASAN build) # mkdir mnt # mount -t btrfs 8.img mnt - Kernel Message [ 449.751861] BTRFS: device fsid 12b338de-a2e9-40fa-a4b0-90e53b7c5773 devid 1 transid 8 /dev/loop0 [ 449.757216] BTRFS info (device loop0): disk space caching is enabled [ 449.757221] BTRFS info (device loop0): has skinny extents [ 449.785096] BTRFS error (device loop0): bad tree block start 0 29396992 [ 449.788629] BTRFS info (device loop0): read error corrected: ino 0 off 29396992 (dev /dev/loop0 sector 73800) [ 449.792965] BTRFS error (device loop0): bad fsid on block 29409280 [ 449.795193] BTRFS info (device loop0): read error corrected: ino 0 off 29409280 (dev /dev/loop0 sector 73824) [ 449.795401] BTRFS info (device loop0): creating UUID tree [ 449.883426] ================================================================== [ 449.886228] BUG: KASAN: use-after-free in try_merge_free_space+0xc0/0x2e0 [ 449.888344] Read of size 8 at addr ffff8801ed10f030 by task mount/1291 [ 449.889947] CPU: 1 PID: 1291 Comm: mount Not tainted 4.17.0-rc5+ #6 [ 449.889951] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 [ 449.889953] Call Trace: [ 449.889976] dump_stack+0x7b/0xb5 [ 449.890274] print_address_description+0x70/0x290 [ 449.890286] kasan_report+0x291/0x390 [ 449.890296] ? try_merge_free_space+0xc0/0x2e0 [ 449.890303] __asan_load8+0x54/0x90 [ 449.890310] try_merge_free_space+0xc0/0x2e0 [ 449.890318] __btrfs_add_free_space+0x96/0x5e0 [ 449.890324] ? kasan_check_write+0x14/0x20 [ 449.890331] ? btrfs_get_block_group+0x1e/0x30 [ 449.890337] ? block_group_cache_tree_search+0xef/0x150 [ 449.890343] unpin_extent_range+0x376/0x670 [ 449.890350] ? __exclude_logged_extent+0x160/0x160 [ 449.890358] btrfs_finish_extent_commit+0x15b/0x490 [ 449.890371] ? __find_get_block+0x106/0x400 [ 449.890378] ? btrfs_prepare_extent_commit+0x1a0/0x1a0 [ 449.890384] ? write_all_supers+0x714/0x1420 [ 449.890394] btrfs_commit_transaction+0xaf4/0xfa0 [ 449.890402] ? btrfs_apply_pending_changes+0xa0/0xa0 [ 449.890407] ? start_transaction+0x153/0x640 [ 449.890414] btrfs_create_uuid_tree+0x6a/0x170 [ 449.890419] open_ctree+0x3b26/0x3ce9 [ 449.890429] ? close_ctree+0x4a0/0x4a0 [ 449.890441] ? bdi_register_va+0x44/0x50 [ 449.890451] ? super_setup_bdi_name+0x11b/0x1a0 [ 449.890457] ? kill_block_super+0x80/0x80 [ 449.890468] ? snprintf+0x96/0xd0 [ 449.890479] btrfs_mount_root+0xae6/0xc60 [ 449.890485] ? btrfs_mount_root+0xae6/0xc60 [ 449.890491] ? pcpu_block_update_hint_alloc+0x1f5/0x2a0 [ 449.890498] ? btrfs_decode_error+0x40/0x40 [ 449.890510] ? find_next_bit+0x57/0x90 [ 449.890517] ? cpumask_next+0x1a/0x20 [ 449.890522] ? pcpu_alloc+0x449/0x8c0 [ 449.890528] ? pcpu_free_area+0x410/0x410 [ 449.890534] ? memcg_kmem_put_cache+0x1b/0xa0 [ 449.890540] ? memcpy+0x45/0x50 [ 449.890547] mount_fs+0x60/0x1a0 [ 449.890553] ? btrfs_decode_error+0x40/0x40 [ 449.890558] ? mount_fs+0x60/0x1a0 [ 449.890565] ? alloc_vfsmnt+0x309/0x360 [ 449.890570] vfs_kern_mount+0x6b/0x1a0 [ 449.890576] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 449.890583] btrfs_mount+0x209/0xb71 [ 449.890589] ? pcpu_block_update_hint_alloc+0x1f5/0x2a0 [ 449.890595] ? btrfs_remount+0x8e0/0x8e0 [ 449.890601] ? find_next_zero_bit+0x2c/0xa0 [ 449.890608] ? find_next_bit+0x57/0x90 [ 449.890613] ? cpumask_next+0x1a/0x20 [ 449.890617] ? pcpu_alloc+0x449/0x8c0 [ 449.890624] ? pcpu_free_area+0x410/0x410 [ 449.890629] ? memcg_kmem_put_cache+0x1b/0xa0 [ 449.890634] ? memcpy+0x45/0x50 [ 449.890641] mount_fs+0x60/0x1a0 [ 449.890646] ? btrfs_remount+0x8e0/0x8e0 [ 449.890652] ? mount_fs+0x60/0x1a0 [ 449.890656] ? alloc_vfsmnt+0x309/0x360 [ 449.890662] vfs_kern_mount+0x6b/0x1a0 [ 449.890668] do_mount+0x34a/0x18a0 [ 449.890673] ? lockref_put_or_lock+0xcf/0x160 [ 449.890680] ? copy_mount_string+0x20/0x20 [ 449.890685] ? memcg_kmem_put_cache+0x1b/0xa0 [ 449.890691] ? kasan_check_write+0x14/0x20 [ 449.890696] ? _copy_from_user+0x6a/0x90 [ 449.890702] ? memdup_user+0x42/0x60 [ 449.890708] ksys_mount+0x83/0xd0 [ 449.890714] __x64_sys_mount+0x67/0x80 [ 449.890723] do_syscall_64+0x78/0x170 [ 449.890729] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 449.890734] RIP: 0033:0x7fc36964fb9a [ 449.890737] RSP: 002b:00007ffd268892f8 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5 [ 449.890744] RAX: ffffffffffffffda RBX: 0000000000e7f030 RCX: 00007fc36964fb9a [ 449.890747] RDX: 0000000000e7f210 RSI: 0000000000e80f30 RDI: 0000000000e87ec0 [ 449.890750] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000014 [ 449.890753] R10: 00000000c0ed0000 R11: 0000000000000202 R12: 0000000000e87ec0 [ 449.890756] R13: 0000000000e7f210 R14: 0000000000000000 R15: 0000000000000003 [ 449.891109] Allocated by task 1291: [ 449.891832] save_stack+0x46/0xd0 [ 449.891838] kasan_kmalloc+0xad/0xe0 [ 449.891843] kasan_slab_alloc+0x11/0x20 [ 449.891848] kmem_cache_alloc+0xd1/0x1e0 [ 449.891854] __btrfs_add_free_space+0x43/0x5e0 [ 449.891859] add_new_free_space+0x22b/0x240 [ 449.891864] btrfs_read_block_groups+0xae3/0xc60 [ 449.891868] open_ctree+0x2cfc/0x3ce9 [ 449.891873] btrfs_mount_root+0xae6/0xc60 [ 449.891878] mount_fs+0x60/0x1a0 [ 449.891883] vfs_kern_mount+0x6b/0x1a0 [ 449.891888] btrfs_mount+0x209/0xb71 [ 449.891893] mount_fs+0x60/0x1a0 [ 449.891897] vfs_kern_mount+0x6b/0x1a0 [ 449.891902] do_mount+0x34a/0x18a0 [ 449.891906] ksys_mount+0x83/0xd0 [ 449.891911] __x64_sys_mount+0x67/0x80 [ 449.891916] do_syscall_64+0x78/0x170 [ 449.891921] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 449.892235] Freed by task 1291: [ 449.892866] save_stack+0x46/0xd0 [ 449.892872] __kasan_slab_free+0x13c/0x1a0 [ 449.892877] kasan_slab_free+0xe/0x10 [ 449.892882] kmem_cache_free+0x89/0x1e0 [ 449.892888] try_merge_free_space+0x274/0x2e0 [ 449.892894] __btrfs_add_free_space+0x96/0x5e0 [ 449.892898] unpin_extent_range+0x376/0x670 [ 449.892904] btrfs_finish_extent_commit+0x15b/0x490 [ 449.892909] btrfs_commit_transaction+0xaf4/0xfa0 [ 449.892913] btrfs_create_uuid_tree+0x6a/0x170 [ 449.892917] open_ctree+0x3b26/0x3ce9 [ 449.892922] btrfs_mount_root+0xae6/0xc60 [ 449.892927] mount_fs+0x60/0x1a0 [ 449.892932] vfs_kern_mount+0x6b/0x1a0 [ 449.892937] btrfs_mount+0x209/0xb71 [ 449.892942] mount_fs+0x60/0x1a0 [ 449.892946] vfs_kern_mount+0x6b/0x1a0 [ 449.892951] do_mount+0x34a/0x18a0 [ 449.892955] ksys_mount+0x83/0xd0 [ 449.892960] __x64_sys_mount+0x67/0x80 [ 449.892965] do_syscall_64+0x78/0x170 [ 449.892970] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 449.893286] The buggy address belongs to the object at ffff8801ed10f000 which belongs to the cache btrfs_free_space of size 72 [ 449.895793] The buggy address is located 48 bytes inside of 72-byte region [ffff8801ed10f000, ffff8801ed10f048) [ 449.898035] The buggy address belongs to the page: [ 449.898979] page:ffffea0007b443c0 count:1 mapcount:0 mapping:0000000000000000 index:0x0 [ 449.900562] flags: 0x2ffff0000000100(slab) [ 449.901379] raw: 02ffff0000000100 0000000000000000 0000000000000000 0000000180270027 [ 449.902881] raw: dead000000000100 dead000000000200 ffff8801e0a676c0 0000000000000000 [ 449.904396] page dumped because: kasan: bad access detected [ 449.905800] Memory state around the buggy address: [ 449.906748] ffff8801ed10ef00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 449.908165] ffff8801ed10ef80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 449.909577] >ffff8801ed10f000: fb fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc [ 449.910969] ^ [ 449.911933] ffff8801ed10f080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 449.913328] ffff8801ed10f100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 449.914720] ================================================================== [ 449.916119] Disabling lock debugging due to kernel taint No kernel crash on plain kernel. - Reason https://elixir.bootlin.com/linux/v4.17-rc5/source/fs/btrfs/free-space-cache.c#L2161 if (left_info && !left_info->bitmap && left_info->offset + left_info->bytes == offset) { if (update_stat) unlink_free_space(ctl, left_info); else __unlink_free_space(ctl, left_info); info->offset = left_info->offset; info->bytes += left_info->bytes; kmem_cache_free(btrfs_free_space_cachep, left_info); merged = true; } return merged; Regarding KASAN report, left_info is already freed but referenced (->bitmap). It is in fact freed just several lines after, namely kmem_cache_free(btrfs_free_space_cachep, left_info); Found by Wen Xu and Po-Ning Tseng from SSLab, Gatech.
Created attachment 276199 [details] KASAN build config (4.17-rc5) used to reproduce the bug
https://patchwork.kernel.org/patch/10503099/