From: Qu Wenruo Date: Wed, 11 Dec 2019 05:00:04 +0000 (+0800) Subject: btrfs: relocation: Fix a KASAN report on btrfs_reloc_pre_snapshot() due to extended... X-Git-Url: http://git.hungrycats.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f7849bea98d786224f726e38fd23b3b51c9cdf4d;p=linux btrfs: relocation: Fix a KASAN report on btrfs_reloc_pre_snapshot() due to extended reloc root lifespan [BUG] When running workload with balance start/cancel, snapshot creation/deletion and fsstress, we can hit the following KASAN report: ================================================================== BUG: KASAN: use-after-free in btrfs_reloc_pre_snapshot+0x85/0xc0 [btrfs] Read of size 4 at addr ffff888157140100 by task btrfs/1822 CPU: 2 PID: 1822 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 btrfs_reloc_pre_snapshot+0x85/0xc0 [btrfs] create_pending_snapshot+0x209/0x15f0 [btrfs] create_pending_snapshots+0x111/0x140 [btrfs] btrfs_commit_transaction+0x7a6/0x1360 [btrfs] btrfs_mksubvol+0x915/0x960 [btrfs] btrfs_ioctl_snap_create_transid+0x1d5/0x1e0 [btrfs] btrfs_ioctl_snap_create_v2+0x1d3/0x270 [btrfs] btrfs_ioctl+0x241b/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] Again, we try to access root->reloc_root without verify if that reloc root is already dead (being freed). [FIX] Check if the root has dead reloc root before accessing it. Reported-by: Zygo Blaxell Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots") Signed-off-by: Qu Wenruo (cherry picked from commit 6fcb3c241e81ef5812388a4ef81dc5c815f643d3) --- diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c index d5723182477d..ed89e3522b13 100644 --- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -4759,7 +4759,8 @@ void btrfs_reloc_pre_snapshot(struct btrfs_pending_snapshot *pending, struct btrfs_root *root = pending->root; struct reloc_control *rc = root->fs_info->reloc_ctl; - if (!root->reloc_root || !rc) + if (!root->reloc_root || !rc || test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, + &root->state)) return; if (!rc->merge_reloc_tree)