[PATCH 0/1] [SRU][O, N, M][PATCH 0/1] Fix UBSAN array-index-out-of-bounds in bcache/bset.c

Mon Jul 1 21:54:49 UTC 2024

BugLink: https://bugs.launchpad.net/bugs/2039368

[Impact]

Currently there are UBSAN warnings that show up when running bcache on jammy HWE, Mantic and noble. For now no side effects have been observed but such an issue could potentially cause a crash or corrupt data.

[Fix]

There is currently a fix upstream provided by the following patch:

* 3a861560ccb3 "bcache: fix variable length array abuse in btree_iter"

[Test Case]

1. Setup bcache on a jammy HWE kernel or mantic or noble machine. This can be done following the steps in this wiki: https://wiki.ubuntu.com/ServerTeam/Bcache
2. Restart the machine
3. After restarting the machine, the following UBSAN warnings and call traces can be seen in dmesg:

[ 3.824281] UBSAN: array-index-out-of-bounds in /build/linux-hwe-6.5-QmAt2N/linux-hwe-6.5-6.5.0/drivers/md/bcache/bset.c:1098:3
[ 3.826338] index 4 is out of range for type 'btree_iter_set [4]'
[ 3.826812] CPU: 13 PID: 184 Comm: kworker/13:1 Not tainted 6.5.0-41-generic #41~22.04.2-Ubuntu
[ 3.827817] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 3.828835] Workqueue: events register_cache_worker [bcache]
[ 3.829429] Call Trace:
[ 3.830626] <TASK>
[ 3.831638] dump_stack_lvl+0x48/0x70
[ 3.832227] dump_stack+0x10/0x20
[ 3.832785] __ubsan_handle_out_of_bounds+0xc6/0x110
[ 3.833357] bch_btree_iter_push+0x4e6/0x4f0 [bcache]
[ 3.834052] bch_btree_node_read_done+0xfc/0x450 [bcache]
[ 3.834653] ? mempool_kfree+0xe/0x20
[ 3.835211] bch_btree_node_read+0xf8/0x1e0 [bcache]
[ 3.835832] ? __pfx_closure_sync_fn+0x10/0x10 [bcache]
[ 3.836474] bch_btree_node_get.part.0+0x160/0x340 [bcache]
[ 3.837161] ? __bch_btree_ptr_invalid+0x60/0xd0 [bcache]
[ 3.837838] ? __pfx_up_write+0x10/0x10
[ 3.838739] bch_btree_node_get+0x16/0x30 [bcache]
[ 3.844949] </TASK>

[ 4.029242] UBSAN: array-index-out-of-bounds in /build/linux-hwe-6.5-QmAt2N/linux-hwe-6.5-6.5.0/drivers/md/bcache/bset.c:1207:3
[ 4.030496] index 14 is out of range for type 'btree_iter_set [4]'
[ 4.030930] CPU: 13 PID: 184 Comm: kworker/13:1 Not tainted 6.5.0-41-generic #41~22.04.2-Ubuntu
[ 4.031841] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 4.032650] Workqueue: events register_cache_worker [bcache]
[ 4.033149] Call Trace:
[ 4.033549] <TASK>
[ 4.033972] dump_stack_lvl+0x48/0x70
[ 4.034418] dump_stack+0x10/0x20
[ 4.034839] __ubsan_handle_out_of_bounds+0xc6/0x110
[ 4.035279] btree_mergesort+0x4d4/0x520 [bcache]
[ 4.035730] ? __pfx_bch_ptr_invalid+0x10/0x10 [bcache]
[ 4.036191] ? __pfx_bch_extent_sort_cmp+0x10/0x10 [bcache]
[ 4.036691] __btree_sort+0x96/0x2d0 [bcache]
[ 4.037182] bch_btree_sort_and_fix_extents+0x1d/0x40 [bcache]
[ 4.037674] bch_btree_node_read_done+0x34d/0x450 [bcache]
[ 4.038172] ? mempool_kfree+0xe/0x20
[ 4.038617] bch_btree_node_read+0xf8/0x1e0 [bcache]
[ 4.039120] ? __pfx_closure_sync_fn+0x10/0x10 [bcache]
[ 4.039659] bch_btree_node_get.part.0+0x160/0x340 [bcache]
[ 4.040220] ? __bch_btree_ptr_invalid+0x60/0xd0 [bcache]
[ 4.040806] ? __pfx_up_write+0x10/0x10
[ 4.041371] bch_btree_node_get+0x16/0x30 [bcache]
[ 4.048339] </TASK>

[ 4.227653] UBSAN: array-index-out-of-bounds in /build/linux-hwe-6.5-QmAt2N/linux-hwe-6.5-6.5.0/drivers/md/bcache/extents.c:281:4
[ 4.228847] index 4 is out of range for type 'btree_iter_set [4]'
[ 4.229472] CPU: 13 PID: 184 Comm: kworker/13:1 Not tainted 6.5.0-41-generic #41~22.04.2-Ubuntu
[ 4.230680] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 4.231954] Workqueue: events register_cache_worker [bcache]
[ 4.232690] Call Trace:
[ 4.233327] <TASK>
[ 4.233935] dump_stack_lvl+0x48/0x70
[ 4.234568] dump_stack+0x10/0x20
[ 4.235219] __ubsan_handle_out_of_bounds+0xc6/0x110
[ 4.235833] bch_extent_sort_fixup+0xb95/0xd70 [bcache]
[ 4.236524] ? __ubsan_handle_out_of_bounds+0xee/0x110
[ 4.237159] ? __pfx_bch_ptr_invalid+0x10/0x10 [bcache]
[ 4.237839] btree_mergesort+0x221/0x520 [bcache]
[ 4.238823] ? __pfx_bch_ptr_invalid+0x10/0x10 [bcache]
[ 4.239800] __btree_sort+0x96/0x2d0 [bcache]
[ 4.240880] bch_btree_sort_and_fix_extents+0x1d/0x40 [bcache]
[ 4.243046] bch_btree_node_read_done+0x34d/0x450 [bcache]
[ 4.245223] ? mempool_kfree+0xe/0x20
[ 4.246311] bch_btree_node_read+0xf8/0x1e0 [bcache]
[ 4.247410] ? __pfx_closure_sync_fn+0x10/0x10 [bcache]
[ 4.248471] bch_btree_node_get.part.0+0x160/0x340 [bcache]
[ 4.248959] ? __bch_btree_ptr_invalid+0x60/0xd0 [bcache]
[ 4.249454] ? __pfx_up_write+0x10/0x10
[ 4.249904] bch_btree_node_get+0x16/0x30 [bcache]
[ 4.255145] </TASK>

[ 4.257388] UBSAN: array-index-out-of-bounds in /build/linux-hwe-6.5-QmAt2N/linux-hwe-6.5-6.5.0/drivers/md/bcache/extents.c:36:18
[ 4.258429] index 14 is out of range for type 'btree_iter_set [4]'
[ 4.258964] CPU: 13 PID: 184 Comm: kworker/13:1 Not tainted 6.5.0-41-generic #41~22.04.2-Ubuntu
[ 4.260073] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 4.261188] Workqueue: events register_cache_worker [bcache]
[ 4.261811] Call Trace:
[ 4.262374] <TASK>
[ 4.262912] dump_stack_lvl+0x48/0x70
[ 4.263502] dump_stack+0x10/0x20
[ 4.264042] __ubsan_handle_out_of_bounds+0xc6/0x110
[ 4.264605] bch_extent_sort_fixup+0xbe5/0xd70 [bcache]
[ 4.265218] ? __ubsan_handle_out_of_bounds+0xee/0x110
[ 4.265821] ? __pfx_bch_ptr_invalid+0x10/0x10 [bcache]
[ 4.266514] btree_mergesort+0x221/0x520 [bcache]
[ 4.267234] ? __pfx_bch_ptr_invalid+0x10/0x10 [bcache]
[ 4.267882] __btree_sort+0x96/0x2d0 [bcache]
[ 4.268508] bch_btree_sort_and_fix_extents+0x1d/0x40 [bcache]
[ 4.269144] bch_btree_node_read_done+0x34d/0x450 [bcache]
[ 4.269825] ? mempool_kfree+0xe/0x20
[ 4.270489] bch_btree_node_read+0xf8/0x1e0 [bcache]
[ 4.271243] ? __pfx_closure_sync_fn+0x10/0x10 [bcache]
[ 4.272293] bch_btree_node_get.part.0+0x160/0x340 [bcache]
[ 4.273260] ? __bch_btree_ptr_invalid+0x60/0xd0 [bcache]
[ 4.274182] ? __pfx_up_write+0x10/0x10
[ 4.274973] bch_btree_node_get+0x16/0x30 [bcache]
[ 4.284807] </TASK>

[ 4.286129] UBSAN: array-index-out-of-bounds in /build/linux-hwe-6.5-QmAt2N/linux-hwe-6.5-6.5.0/drivers/md/bcache/extents.c:291:4
[ 4.286791] index 4 is out of range for type 'btree_iter_set [4]'
[ 4.287231] CPU: 13 PID: 184 Comm: kworker/13:1 Not tainted 6.5.0-41-generic #41~22.04.2-Ubuntu
[ 4.288033] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 4.288863] Workqueue: events register_cache_worker [bcache]
[ 4.289340] Call Trace:
[ 4.289753] <TASK>
[ 4.290168] dump_stack_lvl+0x48/0x70
[ 4.290581] dump_stack+0x10/0x20
[ 4.290984] __ubsan_handle_out_of_bounds+0xc6/0x110
[ 4.291432] bch_extent_sort_fixup+0xb77/0xd70 [bcache]
[ 4.291882] ? __ubsan_handle_out_of_bounds+0xee/0x110
[ 4.292309] ? __pfx_bch_ptr_invalid+0x10/0x10 [bcache]
[ 4.292764] btree_mergesort+0x221/0x520 [bcache]
[ 4.293225] ? __pfx_bch_ptr_invalid+0x10/0x10 [bcache]
[ 4.293683] __btree_sort+0x96/0x2d0 [bcache]
[ 4.294153] bch_btree_sort_and_fix_extents+0x1d/0x40 [bcache]
[ 4.294631] bch_btree_node_read_done+0x34d/0x450 [bcache]
[ 4.295175] ? mempool_kfree+0xe/0x20
[ 4.295671] bch_btree_node_read+0xf8/0x1e0 [bcache]
[ 4.296257] ? __pfx_closure_sync_fn+0x10/0x10 [bcache]
[ 4.296834] bch_btree_node_get.part.0+0x160/0x340 [bcache]
[ 4.297446] ? __bch_btree_ptr_invalid+0x60/0xd0 [bcache]
[ 4.298087] ? __pfx_up_write+0x10/0x10
[ 4.298678] bch_btree_node_get+0x16/0x30 [bcache]
[ 4.306037] </TASK>

[Where problems could occur]

* The patch modifies the way bcache allocates space to the btree iterator. The main problems that could occur are different UBSAN warnings showing up that could possibly trigger a crash much easier than the current array index-out-of-bounds being observed.

Matthew Mirvish (1):
  bcache: fix variable length array abuse in btree_iter

 drivers/md/bcache/bset.c      | 44 +++++++++++++++++------------------
 drivers/md/bcache/bset.h      | 28 ++++++++++++++--------
 drivers/md/bcache/btree.c     | 40 ++++++++++++++++---------------
 drivers/md/bcache/super.c     |  5 ++--
 drivers/md/bcache/sysfs.c     |  2 +-
 drivers/md/bcache/writeback.c | 10 ++++----
 6 files changed, 70 insertions(+), 59 deletions(-)

-- 
2.43.0