Btrfs: fix use-after-free when using the tree modification log
At ctree.c:get_old_root(), we are accessing a root's header owner field
after we have freed the respective extent buffer. This results in an
use-after-free that can lead to crashes, and when CONFIG_DEBUG_PAGEALLOC
is set, results in a stack trace like the following:
[ 3876.799331] stack segment: 0000 [#1] SMP DEBUG_PAGEALLOC PTI
[ 3876.799363] CPU: 0 PID: 15436 Comm: pool Not tainted 5.3.0-rc3-btrfs-next-54 #1
[ 3876.799385] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org 04/01/2014
[ 3876.799433] RIP: 0010:btrfs_search_old_slot+0x652/0xd80 [btrfs]
(...)
[ 3876.799502] RSP: 0018:
ffff9f08c1a2f9f0 EFLAGS:
00010286
[ 3876.799518] RAX:
ffff8dd300000000 RBX:
ffff8dd85a7a9348 RCX:
000000038da26000
[ 3876.799538] RDX:
0000000000000000 RSI:
ffffe522ce368980 RDI:
0000000000000246
[ 3876.799559] RBP:
dae1922adadad000 R08:
0000000008020000 R09:
ffffe522c0000000
[ 3876.799579] R10:
ffff8dd57fd788c8 R11:
000000007511b030 R12:
ffff8dd781ddc000
[ 3876.799599] R13:
ffff8dd9e6240578 R14:
ffff8dd6896f7a88 R15:
ffff8dd688cf90b8
[ 3876.799620] FS:
00007f23ddd97700(0000) GS:
ffff8dda20200000(0000) knlGS:
0000000000000000
[ 3876.799643] CS: 0010 DS: 0000 ES: 0000 CR0:
0000000080050033
[ 3876.799660] CR2:
00007f23d4024000 CR3:
0000000710bb0005 CR4:
00000000003606f0
[ 3876.799682] DR0:
0000000000000000 DR1:
0000000000000000 DR2:
0000000000000000
[ 3876.799703] DR3:
0000000000000000 DR6:
00000000fffe0ff0 DR7:
0000000000000400
[ 3876.799723] Call Trace:
[ 3876.799735] ? do_raw_spin_unlock+0x49/0xc0
[ 3876.799749] ? _raw_spin_unlock+0x24/0x30
[ 3876.799779] resolve_indirect_refs+0x1eb/0xc80 [btrfs]
[ 3876.799810] find_parent_nodes+0x38d/0x1180 [btrfs]
[ 3876.799841] btrfs_check_shared+0x11a/0x1d0 [btrfs]
[ 3876.799870] ? extent_fiemap+0x598/0x6e0 [btrfs]
[ 3876.799895] extent_fiemap+0x598/0x6e0 [btrfs]
[ 3876.799913] do_vfs_ioctl+0x45a/0x700
[ 3876.799926] ksys_ioctl+0x70/0x80
[ 3876.799938] ? trace_hardirqs_off_thunk+0x1a/0x20
[ 3876.799953] __x64_sys_ioctl+0x16/0x20
[ 3876.799965] do_syscall_64+0x62/0x220
[ 3876.799977] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 3876.799993] RIP: 0033:0x7f23e0013dd7
(...)
[ 3876.800056] RSP: 002b:
00007f23ddd96ca8 EFLAGS:
00000246 ORIG_RAX:
0000000000000010
[ 3876.800078] RAX:
ffffffffffffffda RBX:
00007f23d80210f8 RCX:
00007f23e0013dd7
[ 3876.800099] RDX:
00007f23d80210f8 RSI:
00000000c020660b RDI:
0000000000000003
[ 3876.800626] RBP:
000055fa2a2a2440 R08:
0000000000000000 R09:
00007f23ddd96d7c
[ 3876.801143] R10:
00007f23d8022000 R11:
0000000000000246 R12:
00007f23ddd96d80
[ 3876.801662] R13:
00007f23ddd96d78 R14:
00007f23d80210f0 R15:
00007f23ddd96d80
(...)
[ 3876.805107] ---[ end trace
e53161e179ef04f9 ]---
Fix that by saving the root's header owner field into a local variable
before freeing the root's extent buffer, and then use that local variable
when needed.
Fixes:
30b0463a9394d9 ("Btrfs: fix accessing the root pointer in tree mod log functions")
CC: stable@vger.kernel.org # 3.10+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>