On 12/11/19 12:00 AM, Qu Wenruo wrote:
[BUG]
When running a workload with balance start/cancel, snapshot creation and
deletion, and fsstress, we can get the following KASAN report:
==================================================================
BUG: KASAN: use-after-free in should_ignore_root+0x54/0xb0 [btrfs]
Read of size 8 at addr ffff888146e340f0 by task btrfs/1216
CPU: 6 PID: 1216 Comm: btrfs Tainted: G O 5.5.0-rc1-custom+ #40
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Call Trace:
dump_stack+0xc2/0x11a
print_address_description.constprop.0+0x20/0x210
__kasan_report.cold+0x1b/0x41
kasan_report+0x12/0x20
check_memory_region+0x13c/0x1b0
__asan_loadN+0xf/0x20
should_ignore_root+0x54/0xb0 [btrfs]
build_backref_tree+0x11af/0x2280 [btrfs]
relocate_tree_blocks+0x391/0xb80 [btrfs]
relocate_block_group+0x3e5/0xa00 [btrfs]
btrfs_relocate_block_group+0x240/0x4d0 [btrfs]
btrfs_relocate_chunk+0x53/0xf0 [btrfs]
btrfs_balance+0xc91/0x1840 [btrfs]
btrfs_ioctl_balance+0x416/0x4e0 [btrfs]
btrfs_ioctl+0x8af/0x3e60 [btrfs]
do_vfs_ioctl+0x831/0xb10
ksys_ioctl+0x67/0x90
__x64_sys_ioctl+0x43/0x50
do_syscall_64+0x79/0xe0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
[CAUSE]
When should_ignore_root() accessing root->reloc_root, the reloc_root can
be being dropped, thus root->reloc_root can be unreliable.
[FIX]
Check DEAD_RELOC_ROOT bit before accessing root->reloc_root.
Furthermore in the context of should_ignore_root(), if the root has
already gone through tree merge, we don't need to trace that root
anymore.
Thus we need to return 1, for root with dead reloc root.
Reported-by: Zygo Blaxell <ce3g8jdj@xxxxxxxxxxxxxxxxxxxxx>
Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Thanks,
Josef
