[PATCH 4.9 034/101] Btrfs: fix use-after-free when dumping free space

From: Greg Kroah-Hartman
Date: Thu Dec 06 2018 - 09:45:22 EST

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4.9-stable review patch. If anyone has any objections, please let me know.

------------------

From: Filipe Manana <fdmanana@xxxxxxxx>

commit 9084cb6a24bf5838a665af92ded1af8363f9e563 upstream.

We were iterating a block group's free space cache rbtree without locking
first the lock that protects it (the free_space_ctl->free_space_offset
rbtree is protected by the free_space_ctl->tree_lock spinlock).

KASAN reported an use-after-free problem when iterating such a rbtree due
to a concurrent rbtree delete:

[ 9520.359168] ==================================================================
[ 9520.359656] BUG: KASAN: use-after-free in rb_next+0x13/0x90
[ 9520.359949] Read of size 8 at addr ffff8800b7ada500 by task btrfs-transacti/1721
[ 9520.360357]
[ 9520.360530] CPU: 4 PID: 1721 Comm: btrfs-transacti Tainted: G L 4.19.0-rc8-nbor #555
[ 9520.360990] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[ 9520.362682] Call Trace:
[ 9520.362887] dump_stack+0xa4/0xf5
[ 9520.363146] print_address_description+0x78/0x280
[ 9520.363412] kasan_report+0x263/0x390
[ 9520.363650] ? rb_next+0x13/0x90
[ 9520.363873] __asan_load8+0x54/0x90
[ 9520.364102] rb_next+0x13/0x90
[ 9520.364380] btrfs_dump_free_space+0x146/0x160 [btrfs]
[ 9520.364697] dump_space_info+0x2cd/0x310 [btrfs]
[ 9520.364997] btrfs_reserve_extent+0x1ee/0x1f0 [btrfs]
[ 9520.365310] __btrfs_prealloc_file_range+0x1cc/0x620 [btrfs]
[ 9520.365646] ? btrfs_update_time+0x180/0x180 [btrfs]
[ 9520.365923] ? _raw_spin_unlock+0x27/0x40
[ 9520.366204] ? btrfs_alloc_data_chunk_ondemand+0x2c0/0x5c0 [btrfs]
[ 9520.366549] btrfs_prealloc_file_range_trans+0x23/0x30 [btrfs]
[ 9520.366880] cache_save_setup+0x42e/0x580 [btrfs]
[ 9520.367220] ? btrfs_check_data_free_space+0xd0/0xd0 [btrfs]
[ 9520.367518] ? lock_downgrade+0x2f0/0x2f0
[ 9520.367799] ? btrfs_write_dirty_block_groups+0x11f/0x6e0 [btrfs]
[ 9520.368104] ? kasan_check_read+0x11/0x20
[ 9520.368349] ? do_raw_spin_unlock+0xa8/0x140
[ 9520.368638] btrfs_write_dirty_block_groups+0x2af/0x6e0 [btrfs]
[ 9520.368978] ? btrfs_start_dirty_block_groups+0x870/0x870 [btrfs]
[ 9520.369282] ? do_raw_spin_unlock+0xa8/0x140
[ 9520.369534] ? _raw_spin_unlock+0x27/0x40
[ 9520.369811] ? btrfs_run_delayed_refs+0x1b8/0x230 [btrfs]
[ 9520.370137] commit_cowonly_roots+0x4b9/0x610 [btrfs]
[ 9520.370560] ? commit_fs_roots+0x350/0x350 [btrfs]
[ 9520.370926] ? btrfs_run_delayed_refs+0x1b8/0x230 [btrfs]
[ 9520.371285] btrfs_commit_transaction+0x5e5/0x10e0 [btrfs]
[ 9520.371612] ? btrfs_apply_pending_changes+0x90/0x90 [btrfs]
[ 9520.371943] ? start_transaction+0x168/0x6c0 [btrfs]
[ 9520.372257] transaction_kthread+0x21c/0x240 [btrfs]
[ 9520.372537] kthread+0x1d2/0x1f0
[ 9520.372793] ? btrfs_cleanup_transaction+0xb50/0xb50 [btrfs]
[ 9520.373090] ? kthread_park+0xb0/0xb0
[ 9520.373329] ret_from_fork+0x3a/0x50
[ 9520.373567]
[ 9520.373738] Allocated by task 1804:
[ 9520.373974] kasan_kmalloc+0xff/0x180
[ 9520.374208] kasan_slab_alloc+0x11/0x20
[ 9520.374447] kmem_cache_alloc+0xfc/0x2d0
[ 9520.374731] __btrfs_add_free_space+0x40/0x580 [btrfs]
[ 9520.375044] unpin_extent_range+0x4f7/0x7a0 [btrfs]
[ 9520.375383] btrfs_finish_extent_commit+0x15f/0x4d0 [btrfs]
[ 9520.375707] btrfs_commit_transaction+0xb06/0x10e0 [btrfs]
[ 9520.376027] btrfs_alloc_data_chunk_ondemand+0x237/0x5c0 [btrfs]
[ 9520.376365] btrfs_check_data_free_space+0x81/0xd0 [btrfs]
[ 9520.376689] btrfs_delalloc_reserve_space+0x25/0x80 [btrfs]
[ 9520.377018] btrfs_direct_IO+0x42e/0x6d0 [btrfs]
[ 9520.377284] generic_file_direct_write+0x11e/0x220
[ 9520.377587] btrfs_file_write_iter+0x472/0xac0 [btrfs]
[ 9520.377875] aio_write+0x25c/0x360
[ 9520.378106] io_submit_one+0xaa0/0xdc0
[ 9520.378343] __se_sys_io_submit+0xfa/0x2f0
[ 9520.378589] __x64_sys_io_submit+0x43/0x50
[ 9520.378840] do_syscall_64+0x7d/0x240
[ 9520.379081] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 9520.379387]
[ 9520.379557] Freed by task 1802:
[ 9520.379782] __kasan_slab_free+0x173/0x260
[ 9520.380028] kasan_slab_free+0xe/0x10
[ 9520.380262] kmem_cache_free+0xc1/0x2c0
[ 9520.380544] btrfs_find_space_for_alloc+0x4cd/0x4e0 [btrfs]
[ 9520.380866] find_free_extent+0xa99/0x17e0 [btrfs]
[ 9520.381166] btrfs_reserve_extent+0xd5/0x1f0 [btrfs]
[ 9520.381474] btrfs_get_blocks_direct+0x60b/0xbd0 [btrfs]
[ 9520.381761] __blockdev_direct_IO+0x10ee/0x58a1
[ 9520.382059] btrfs_direct_IO+0x25a/0x6d0 [btrfs]
[ 9520.382321] generic_file_direct_write+0x11e/0x220
[ 9520.382623] btrfs_file_write_iter+0x472/0xac0 [btrfs]
[ 9520.382904] aio_write+0x25c/0x360
[ 9520.383172] io_submit_one+0xaa0/0xdc0
[ 9520.383416] __se_sys_io_submit+0xfa/0x2f0
[ 9520.383678] __x64_sys_io_submit+0x43/0x50
[ 9520.383927] do_syscall_64+0x7d/0x240
[ 9520.384165] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 9520.384439]
[ 9520.384610] The buggy address belongs to the object at ffff8800b7ada500
which belongs to the cache btrfs_free_space of size 72
[ 9520.385175] The buggy address is located 0 bytes inside of
72-byte region [ffff8800b7ada500, ffff8800b7ada548)
[ 9520.385691] The buggy address belongs to the page:
[ 9520.385957] page:ffffea0002deb680 count:1 mapcount:0 mapping:ffff880108a1d700 index:0x0 compound_mapcount: 0
[ 9520.388030] flags: 0x8100(slab|head)
[ 9520.388281] raw: 0000000000008100 ffffea0002deb608 ffffea0002728808 ffff880108a1d700
[ 9520.388722] raw: 0000000000000000 0000000000130013 00000001ffffffff 0000000000000000
[ 9520.389169] page dumped because: kasan: bad access detected
[ 9520.389473]
[ 9520.389658] Memory state around the buggy address:
[ 9520.389943] ffff8800b7ada400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 9520.390368] ffff8800b7ada480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 9520.390796] >ffff8800b7ada500: fb fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc
[ 9520.391223] ^
[ 9520.391461] ffff8800b7ada580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 9520.391885] ffff8800b7ada600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 9520.392313] ==================================================================
[ 9520.392772] BTRFS critical (device vdc): entry offset 2258497536, bytes 131072, bitmap no
[ 9520.393247] BUG: unable to handle kernel NULL pointer dereference at 0000000000000011
[ 9520.393705] PGD 800000010dbab067 P4D 800000010dbab067 PUD 107551067 PMD 0
[ 9520.394059] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
[ 9520.394378] CPU: 4 PID: 1721 Comm: btrfs-transacti Tainted: G B L 4.19.0-rc8-nbor #555
[ 9520.394858] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[ 9520.395350] RIP: 0010:rb_next+0x3c/0x90
[ 9520.396461] RSP: 0018:ffff8801074ff780 EFLAGS: 00010292
[ 9520.396762] RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffffffff81b5ac4c
[ 9520.397115] RDX: 0000000000000000 RSI: 0000000000000008 RDI: 0000000000000011
[ 9520.397468] RBP: ffff8801074ff7a0 R08: ffffed0021d64ccc R09: ffffed0021d64ccc
[ 9520.397821] R10: 0000000000000001 R11: ffffed0021d64ccb R12: ffff8800b91e0000
[ 9520.398188] R13: ffff8800a3ceba48 R14: ffff8800b627bf80 R15: 0000000000020000
[ 9520.398555] FS: 0000000000000000(0000) GS:ffff88010eb00000(0000) knlGS:0000000000000000
[ 9520.399007] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 9520.399335] CR2: 0000000000000011 CR3: 0000000106b52000 CR4: 00000000000006a0
[ 9520.399679] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 9520.400023] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 9520.400400] Call Trace:
[ 9520.400648] btrfs_dump_free_space+0x146/0x160 [btrfs]
[ 9520.400974] dump_space_info+0x2cd/0x310 [btrfs]
[ 9520.401287] btrfs_reserve_extent+0x1ee/0x1f0 [btrfs]
[ 9520.401609] __btrfs_prealloc_file_range+0x1cc/0x620 [btrfs]
[ 9520.401952] ? btrfs_update_time+0x180/0x180 [btrfs]
[ 9520.402232] ? _raw_spin_unlock+0x27/0x40
[ 9520.402522] ? btrfs_alloc_data_chunk_ondemand+0x2c0/0x5c0 [btrfs]
[ 9520.402882] btrfs_prealloc_file_range_trans+0x23/0x30 [btrfs]
[ 9520.403261] cache_save_setup+0x42e/0x580 [btrfs]
[ 9520.403570] ? btrfs_check_data_free_space+0xd0/0xd0 [btrfs]
[ 9520.403871] ? lock_downgrade+0x2f0/0x2f0
[ 9520.404161] ? btrfs_write_dirty_block_groups+0x11f/0x6e0 [btrfs]
[ 9520.404481] ? kasan_check_read+0x11/0x20
[ 9520.404732] ? do_raw_spin_unlock+0xa8/0x140
[ 9520.405026] btrfs_write_dirty_block_groups+0x2af/0x6e0 [btrfs]
[ 9520.405375] ? btrfs_start_dirty_block_groups+0x870/0x870 [btrfs]
[ 9520.405694] ? do_raw_spin_unlock+0xa8/0x140
[ 9520.405958] ? _raw_spin_unlock+0x27/0x40
[ 9520.406243] ? btrfs_run_delayed_refs+0x1b8/0x230 [btrfs]
[ 9520.406574] commit_cowonly_roots+0x4b9/0x610 [btrfs]
[ 9520.406899] ? commit_fs_roots+0x350/0x350 [btrfs]
[ 9520.407253] ? btrfs_run_delayed_refs+0x1b8/0x230 [btrfs]
[ 9520.407589] btrfs_commit_transaction+0x5e5/0x10e0 [btrfs]
[ 9520.407925] ? btrfs_apply_pending_changes+0x90/0x90 [btrfs]
[ 9520.408262] ? start_transaction+0x168/0x6c0 [btrfs]
[ 9520.408582] transaction_kthread+0x21c/0x240 [btrfs]
[ 9520.408870] kthread+0x1d2/0x1f0
[ 9520.409138] ? btrfs_cleanup_transaction+0xb50/0xb50 [btrfs]
[ 9520.409440] ? kthread_park+0xb0/0xb0
[ 9520.409682] ret_from_fork+0x3a/0x50
[ 9520.410508] Dumping ftrace buffer:
[ 9520.410764] (ftrace buffer empty)
[ 9520.411007] CR2: 0000000000000011
[ 9520.411297] ---[ end trace 01a0863445cf360a ]---
[ 9520.411568] RIP: 0010:rb_next+0x3c/0x90
[ 9520.412644] RSP: 0018:ffff8801074ff780 EFLAGS: 00010292
[ 9520.412932] RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffffffff81b5ac4c
[ 9520.413274] RDX: 0000000000000000 RSI: 0000000000000008 RDI: 0000000000000011
[ 9520.413616] RBP: ffff8801074ff7a0 R08: ffffed0021d64ccc R09: ffffed0021d64ccc
[ 9520.414007] R10: 0000000000000001 R11: ffffed0021d64ccb R12: ffff8800b91e0000
[ 9520.414349] R13: ffff8800a3ceba48 R14: ffff8800b627bf80 R15: 0000000000020000
[ 9520.416074] FS: 0000000000000000(0000) GS:ffff88010eb00000(0000) knlGS:0000000000000000
[ 9520.416536] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 9520.416848] CR2: 0000000000000011 CR3: 0000000106b52000 CR4: 00000000000006a0
[ 9520.418477] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 9520.418846] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 9520.419204] Kernel panic - not syncing: Fatal exception
[ 9520.419666] Dumping ftrace buffer:
[ 9520.419930] (ftrace buffer empty)
[ 9520.420168] Kernel Offset: disabled
[ 9520.420406] ---[ end Kernel panic - not syncing: Fatal exception ]---

Fix this by acquiring the respective lock before iterating the rbtree.

Reported-by: Nikolay Borisov <nborisov@xxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx # 4.4+
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Cc: Nikolay Borisov <nborisov@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/btrfs/free-space-cache.c | 2 ++
1 file changed, 2 insertions(+)

--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -2464,6 +2464,7 @@ void btrfs_dump_free_space(struct btrfs_
struct rb_node *n;
int count = 0;

+ spin_lock(&ctl->tree_lock);
for (n = rb_first(&ctl->free_space_offset); n; n = rb_next(n)) {
info = rb_entry(n, struct btrfs_free_space, offset_index);
if (info->bytes >= bytes && !block_group->ro)
@@ -2473,6 +2474,7 @@ void btrfs_dump_free_space(struct btrfs_
info->offset, info->bytes,
(info->bitmap) ? "yes" : "no");
}
+ spin_unlock(&ctl->tree_lock);
btrfs_info(block_group->fs_info, "block group has cluster?: %s",
list_empty(&block_group->cluster_list) ? "no" : "yes");
btrfs_info(block_group->fs_info,

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