In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
btrfs: fix use-after-free on reloc root after error in insert_dirty_subvol()<\/p>\n
If during relocation we fail in insert_dirty_subvol() because
\nbtrfs_update_reloc_root() returned an error, we will leave a root’s
\nreloc_root field pointing to a reloc root that was freed instead of NULL,
\nresulting later in a use-after-free, or double free attempt during
\nunmount.<\/p>\n
The sequence of steps is this:<\/p>\n
1) During relocation the call to btrfs_update_reloc_root() in
\n insert_dirty_subvol() fails, so insert_dirty_subvol() returns the
\n error to merge_reloc_root() without adding the root to the list
\n rc->dirty_subvol_roots;<\/p>\n
2) Then merge_reloc_root() aborts the current transaction because
\n insert_dirty_subvol() returned an error;<\/p>\n
3) Up the call chain, merge_reloc_roots() gets the error, adds the
\n reloc root for root X to the local reloc_roots list and jumps to the
\n ‘out’ label, where it calls free_reloc_roots() to free all the reloc
\n roots in the local reloc_roots list. This frees the reloc root for
\n root X;<\/p>\n
4) We go up the call chain to relocate_block_group() which calls
\n clean_dirty_subvols() to go over dirty roots and set their
\n ->reloc_root field to NULL, but root X is not in the dirty_subvol_roots
\n list, so its ->reloc_root still points to a reloc root;<\/p>\n
5) Relocation finishes, with an error and a transaction abort, but the
\n ->reloc_root field for root X still points to the reloc root that was
\n freed in step 3;<\/p>\n
6) When unmounting the fs we end up calling:<\/p>\n
btrfs_free_fs_roots()
\n btrfs_drop_and_free_fs_root()
\n –> calls btrfs_put_root() against root X’s ->reloc_root
\n which is not NULL and points to the already freed
\n reloc root in step 4 above<\/p>\n
Resulting in a use-after-free to a double free attempt.<\/p>\n
Syzbot reported this with the following dmesg\/syslog:<\/p>\n
[ 106.004389][ T5339] BTRFS error (device loop0 state A): Transaction aborted (error -5)
\n [ 106.014266][ T5339] BTRFS: error (device loop0 state A) in merge_reloc_root:1655: errno=-5 IO failure
\n [ 106.021891][ T1061] BTRFS error (device loop0 state A): error while writing out transaction: -5
\n [ 106.026964][ T1061] BTRFS warning (device loop0 state A): Skipping commit of aborted transaction.
\n [ 106.033807][ T5340] BTRFS error (device loop0 state A): bdev \/dev\/loop0 errs: wr 3, rd 0, flush 0, corrupt 0, gen 0
\n [ 106.039265][ T1061] BTRFS: error (device loop0 state A) in cleanup_transaction:2067: errno=-5 IO failure
\n [ 106.044382][ T5339] BTRFS info (device loop0 state EA): forced readonly
\n [ 106.074329][ T5339] BTRFS: error (device loop0 state EA) in merge_reloc_roots:1887: errno=-5 IO failure
\n [ 106.081004][ T5356] BTRFS info (device loop0 state EA): scrub: started on devid 1
\n [ 106.085611][ T5339] BTRFS info (device loop0 state EA): balance: ended with status: -30
\n [ 106.089517][ T5356] BTRFS info (device loop0 state EA): scrub: not finished on devid 1 with status: -30
\n [ 106.662365][ T5338] BTRFS info (device loop0 state EA): last unmount of filesystem 3a375e4e-b156-4d76-a2ad-16e198ce1409
\n [ 106.682946][ T5338] ==================================================================
\n [ 106.686574][ T5338] BUG: KASAN: slab-use-after-free in btrfs_put_root+0x2f\/0x250
\n [ 106.690090][ T5338] Write of size 4 at addr ffff88803f978630 by task syz.0.0\/5338
\n [ 106.693173][ T5338]
\n [ 106.694279][ T5338] CPU: 0 UID: 0 PID: 5338 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
\n [ 106.694293][ T5338] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04\/01\/2014
\n [ 106.694300][ T5338] Call Trace:
\n [ 106.694308][ T5338]
\n [ 106.694314][ T5338] dump_stack_lvl+0xe8\/0x150
\n [ 106.694331][ T5338] print_address_description+0x55\/0x1e0
\n [ 106.694343][ T5338] ? btrfs_put_root+0x2f\/0x250
\n [ 106.694358][ T5338] print_report+0x58\/0x70
\n [ 106.
\n—truncated—<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
btrfs: fix use-after-free on reloc root after error in insert_dirty_subvol()<\/p>\n
If during relocation we fail in insert_dirty_subvol()<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-28615","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/28615","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=28615"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=28615"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=28615"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}