[syzbot] KASAN: slab-use-after-free Write in o2hb_region_dev_store

[syzbot] KASAN: slab-use-after-free Write in o2hb_region_dev_store

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    bc35965f6940 Merge tag 'mm-hotfixes-stable-2026-09-03-17-4..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=119c84f9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5c3949d762a91f
dashboard link: https://syzkaller.appspot.com/bug?extid=3025e3e8fc0b928af8f5
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1714a8f9580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3025e3e8fc0b928af8f5@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in o2hb_map_slot_data fs/ocfs2/cluster/heartbeat.c:1811 [inline]
BUG: KASAN: slab-use-after-free in o2hb_region_dev_store+0x1751/0x1b00 fs/ocfs2/cluster/heartbeat.c:1936
Write of size 8 at addr ffff8880262b82e8 by task syz.3.20/6459

CPU: 2 UID: 0 PID: 6459 Comm: syz.3.20 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
 o2hb_map_slot_data fs/ocfs2/cluster/heartbeat.c:1811 [inline]
 o2hb_region_dev_store+0x1751/0x1b00 fs/ocfs2/cluster/heartbeat.c:1936
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x302/0x4e0 fs/configfs/file.c:229
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6af/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f79d5d9e019
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f79d6c1c028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f79d6025fa0 RCX: 00007f79d5d9e019
RDX: 0000000000000001 RSI: 00002000000005c0 RDI: 0000000000000004
RBP: 00007f79d5e3500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f79d6026038 R14: 00007f79d6025fa0 R15: 00007ffc42008128
 </TASK>

Allocated by task 6459:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5414 [inline]
 __kmalloc_noprof+0x32f/0x840 mm/slub.c:5439
 _kmalloc_noprof include/linux/slab.h:995 [inline]
 _kzalloc_noprof include/linux/slab.h:1312 [inline]
 o2hb_map_slot_data fs/ocfs2/cluster/heartbeat.c:1802 [inline]
 o2hb_region_dev_store+0x88b/0x1b00 fs/ocfs2/cluster/heartbeat.c:1936
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x302/0x4e0 fs/configfs/file.c:229
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6af/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6458:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2748 [inline]
 slab_free mm/slub.c:6499 [inline]
 kfree+0x22b/0x6d0 mm/slub.c:6792
 o2hb_unmap_slot_data+0x190/0x330 fs/ocfs2/cluster/heartbeat.c:1596
 o2hb_region_dev_store+0x112e/0x1b00 fs/ocfs2/cluster/heartbeat.c:2027
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x302/0x4e0 fs/configfs/file.c:229
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6af/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880262b8200
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 232 bytes inside of
 freed 256-byte region [ffff8880262b8200, ffff8880262b8300)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x262b8
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801c042b40 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801c042b40 dead000000000100 dead000000000122
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffffffffffff81 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 39, tgid 39 (kdevtmpfs), ts 6186544854
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1871
 prep_new_page mm/page_alloc.c:1879 [inline]
 get_page_from_freelist+0x110d/0x35d0 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x2eb/0x3300 mm/page_alloc.c:5436
 alloc_slab_page mm/slub.c:3347 [inline]
 allocate_slab mm/slub.c:3462 [inline]
 new_slab+0xa9/0x6e0 mm/slub.c:3513
 refill_objects+0xe3/0x410 mm/slub.c:7410
 refill_sheaf mm/slub.c:2885 [inline]
 __pcs_replace_empty_main+0x35e/0x650 mm/slub.c:4774
 alloc_from_pcs mm/slub.c:4850 [inline]
 slab_alloc_node mm/slub.c:4984 [inline]
 __do_kmalloc_node mm/slub.c:5413 [inline]
 __kmalloc_noprof+0x67c/0x840 mm/slub.c:5439
 _kmalloc_noprof include/linux/slab.h:995 [inline]
 _kmalloc_array_noprof include/linux/slab.h:1211 [inline]
 security_inode_init_security+0x113/0x370 security/security.c:1347
 shmem_mknod+0x2ce/0x480 mm/shmem.c:3838
 vfs_mknod+0x3a5/0x7f0 fs/namei.c:5269
 handle_create drivers/base/devtmpfs.c:232 [inline]
 handle drivers/base/devtmpfs.c:384 [inline]
 devtmpfs_work_loop+0x48d/0xae4 drivers/base/devtmpfs.c:399
 devtmpfsd+0x3f/0x50 drivers/base/devtmpfs.c:441
 kthread+0x373/0x450 kernel/kthread.c:436
 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8880262b8180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880262b8200: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880262b8280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8880262b8300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880262b8380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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Forwarded: [PATCH] ocfs2: fix use-after-free in o2hb_region_dev_store

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] ocfs2: fix use-after-free in o2hb_region_dev_store
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Concurrent writes to a region's "dev" attribute can race, letting two
tasks both allocate/free reg->hr_slot_data for the same region and
causing a use-after-free. Add a per-region mutex to serialize
o2hb_region_dev_store() against itself and against
o2hb_region_release().

Reported-by: syzbot+3025e3e8fc0b928af8f5@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3025e3e8fc0b928af8f5
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/ocfs2/cluster/heartbeat.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
index 1c3def99bb07..6f03de1b6d4a 100644
--- a/fs/ocfs2/cluster/heartbeat.c
+++ b/fs/ocfs2/cluster/heartbeat.c
@@ -273,6 +273,9 @@ struct o2hb_region {
 
 	/* last hb status, 0 for success, other value for error. */
 	int			hr_last_hb_status;
+	/* Serializes dev_store() against itself and region_release() */
+	struct mutex            hr_dev_write_mutex;
+
 };
 
 static inline struct block_device *reg_bdev(struct o2hb_region *reg)
@@ -1616,7 +1619,10 @@ static void o2hb_region_release(struct config_item *item)
 
 	o2hb_quiesce_timeout(reg);
 	o2net_unregister_and_flush_handler_list(&reg->hr_handler_list);
+
+	mutex_lock(&reg->hr_dev_write_mutex);
 	o2hb_unmap_slot_data(reg);
+	mutex_unlock(&reg->hr_dev_write_mutex);
 
 	if (reg->hr_bdev_file)
 		fput(reg->hr_bdev_file);
@@ -1879,9 +1885,6 @@ static ssize_t o2hb_region_dev_store(struct config_item *item,
 	ssize_t ret = -EINVAL;
 	int live_threshold;
 
-	if (reg->hr_bdev_file)
-		return -EINVAL;
-
 	/* We can't heartbeat without having had our node number
 	 * configured yet. */
 	reg->hr_node_num = o2nm_this_node();
@@ -1906,12 +1909,20 @@ static ssize_t o2hb_region_dev_store(struct config_item *item,
 	if (!S_ISBLK(fd_file(f)->f_mapping->host->i_mode))
 		return -EINVAL;
 
+	if (mutex_lock_interruptible(&reg->hr_dev_write_mutex))
+		return -ERESTARTSYS;
+
+	if (reg->hr_bdev_file) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
 	reg->hr_bdev_file = bdev_file_open_by_dev(fd_file(f)->f_mapping->host->i_rdev,
 			BLK_OPEN_WRITE | BLK_OPEN_READ, NULL, NULL);
 	if (IS_ERR(reg->hr_bdev_file)) {
 		ret = PTR_ERR(reg->hr_bdev_file);
 		reg->hr_bdev_file = NULL;
-		return ret;
+		goto out_unlock;
 	}
 
 	sectsize = bdev_logical_block_size(reg_bdev(reg));
@@ -2029,6 +2040,8 @@ static ssize_t o2hb_region_dev_store(struct config_item *item,
 		fput(reg->hr_bdev_file);
 		reg->hr_bdev_file = NULL;
 	}
+out_unlock:
+	mutex_unlock(&reg->hr_dev_write_mutex);
 	return ret;
 }
 
@@ -2149,6 +2162,8 @@ static struct config_item *o2hb_heartbeat_group_make_item(struct config_group *g
 
 	config_item_init_type_name(&reg->hr_item, name, &o2hb_region_type);
 
+	mutex_init(&reg->hr_dev_write_mutex);
+
 	/* this is the same way to generate msg key as dlm, for local heartbeat,
 	 * name is also the same, so make initial crc value different to avoid
 	 * message key conflict.
-- 
2.34.1

Re: [syzbot] KASAN: slab-use-after-free Write in o2hb_region_dev_store

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+3025e3e8fc0b928af8f5@syzkaller.appspotmail.com
Tested-by: syzbot+3025e3e8fc0b928af8f5@syzkaller.appspotmail.com

Tested on:

commit:         654ae5d7 Merge tag 'drm-fixes-2026-09-05' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13d8e125580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5c3949d762a91f
dashboard link: https://syzkaller.appspot.com/bug?extid=3025e3e8fc0b928af8f5
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10349215580000

Note: testing is done by a robot and is best-effort only.