[PATCH] ocfs2/cluster: serialize heartbeat block count with device setup

[Cen Zhang <zzzccc427@gmail.com>]

A heartbeat region's hr_blocks must match the number of slots allocated
in hr_slots until its thread stops. o2hb_region_blocks_store() checks
hr_bdev_file before updating hr_blocks, but neither operation is
serialized with device publication in o2hb_region_dev_store().

Writes to blocks and dev through separate configfs opens can overlap.
The buffer mutex is per open, and both callbacks hold frag_sem for read.
With an initial count N, the following order is possible:

  blocks writer               device writer
  -------------               -------------
  check hr_bdev_file == NULL
                              publish hr_bdev_file
                              allocate N slots in o2hb_map_slot_data()
                              start o2hb_thread() and return
  store hr_blocks = M, M > N
  return

After both writes finish, normal region removal calls kthread_stop().
o2hb_thread() iterates over the enlarged count and passes &hr_slots[N]
to o2hb_shutdown_slot(), which reads ds_node_num beyond the allocation.

Recheck the device guard and update hr_blocks under o2hb_live_lock, and
publish the device file under the same lock. Open the device into a
local pointer to keep the sleeping open outside the spinlock. A blocks
write then either completes before publication and determines the slot
count, or sees the published file and returns -EINVAL. Clear the file
under the same lock after failed-start cleanup has stopped the thread
and unmapped the slots, so configuration can resume safely.

KASAN report as below:

    BUG: KASAN: slab-out-of-bounds in o2hb_thread+0xc62/0xe90
    Read of size 1 at addr ffff888107829ac0 by task o2hb-pmbd-regio/497

    CPU: 3 UID: 0 PID: 497 Comm: o2hb-pmbd-regio Not tainted 7.3.0-rc4-next-20260921-pmb-ocfs2-functional-v1+ #1 PREEMPT(lazy)
    Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
    Call Trace:
     <TASK>
     dump_stack_lvl+0x93/0xd0
     print_report+0xce/0x630
     ? o2hb_thread+0xc62/0xe90
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? __virt_addr_valid+0x20e/0x420
     ? o2hb_thread+0xc62/0xe90
     kasan_report+0xe0/0x110
     ? o2hb_thread+0xc62/0xe90
     o2hb_thread+0xc62/0xe90
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? __pfx_o2hb_thread+0x10/0x10
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? __lock_acquire+0x5a3/0x2140
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? lockdep_hardirqs_on_prepare+0xeb/0x1a0
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? trace_hardirqs_on+0x18/0x160
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? __pfx_o2hb_thread+0x10/0x10
     ? kthread+0x351/0x460
     kthread+0x351/0x460
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? __pfx_kthread+0x10/0x10
     ret_from_fork+0x659/0x940
     ? __pfx_ret_from_fork+0x10/0x10
     ? srso_alias_return_thunk+0x5/0xfbef5
     ? __switch_to+0x74f/0xf70
     ? __pfx_kthread+0x10/0x10
     ret_from_fork_asm+0x1a/0x30
     </TASK>

    Allocated by task 496:
     kasan_save_stack+0x33/0x60
     kasan_save_track+0x14/0x30
     __kasan_kmalloc+0xaa/0xb0
     __kmalloc_noprof+0x2de/0x780
     o2hb_region_dev_store+0x7c4/0x1c70
     configfs_write_iter+0x2f9/0x4f0
     vfs_write+0x639/0x1010
     ksys_write+0x111/0x200
     do_syscall_64+0x114/0x620
     entry_SYSCALL_64_after_hwframe+0x77/0x7f

    The buggy address belongs to the object at ffff888107829a80
     which belongs to the cache kmalloc-64 of size 64
    The buggy address is located 8 bytes to the right of
     allocated 56-byte region [ffff888107829a80, ffff888107829ab8)

(Page and memory-state dump omitted.)

Fixes: a7f6a5fb4bde ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
Cc: <stable@vger.kernel.org>
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Assisted-by: LLM
---
 fs/ocfs2/cluster/heartbeat.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
index b45adc39aacc..7448ee53aebe 100644
--- a/fs/ocfs2/cluster/heartbeat.c
+++ b/fs/ocfs2/cluster/heartbeat.c
@@ -1746,7 +1746,13 @@ static ssize_t o2hb_region_blocks_store(struct config_item *item,
 	if (tmp > O2NM_MAX_NODES || tmp == 0)
 		return -ERANGE;
 
+	spin_lock(&o2hb_live_lock);
+	if (reg->hr_bdev_file) {
+		spin_unlock(&o2hb_live_lock);
+		return -EINVAL;
+	}
 	reg->hr_blocks = (unsigned int)tmp;
+	spin_unlock(&o2hb_live_lock);
 
 	return count;
 }
@@ -1878,6 +1884,7 @@ static ssize_t o2hb_region_dev_store(struct config_item *item,
 {
 	struct o2hb_region *reg = to_o2hb_region(item);
 	struct task_struct *hb_task;
+	struct file *bdev_file;
 	long fd;
 	int sectsize;
 	char *p = (char *)page;
@@ -1911,13 +1918,22 @@ static ssize_t o2hb_region_dev_store(struct config_item *item,
 	if (!S_ISBLK(fd_file(f)->f_mapping->host->i_mode))
 		return -EINVAL;
 
-	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;
+	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(bdev_file))
+		return PTR_ERR(bdev_file);
+
+	/* Freeze hr_blocks before allocating the slot array. */
+	spin_lock(&o2hb_live_lock);
+	if (reg->hr_bdev_file) {
+		spin_unlock(&o2hb_live_lock);
+		fput(bdev_file);
+		return -EINVAL;
 	}
+	reg->hr_bdev_file = bdev_file;
+	spin_unlock(&o2hb_live_lock);
 
 	sectsize = bdev_logical_block_size(reg_bdev(reg));
 	if (sectsize != reg->hr_block_bytes) {
@@ -2036,7 +2052,9 @@ out:
 		o2hb_unmap_slot_data(reg);
 
 		fput(reg->hr_bdev_file);
+		spin_lock(&o2hb_live_lock);
 		reg->hr_bdev_file = NULL;
+		spin_unlock(&o2hb_live_lock);
 	}
 	return ret;
 }