Re: [BUG] dm-integrity: mode R resume NULL deref when DIRTY_BITMAP is set

On Mon, 17 Aug 2026, Yu Junzhe wrote:

> Hello,
> 
> I am reporting a null-pointer dereference in dm-integrity resume: recovery
> mode R skips journal allocation, but dm_integrity_resume() still issues
> journal I/O when the on-disk superblock has SB_FLAG_DIRTY_BITMAP.
> 
> Summary
> =======
> 
> create_journal() runs only when mode != 'R', so ic->journal stays NULL.
> Resume treats DIRTY_BITMAP as "journal pages hold a bitmap" and calls
> rw_journal_sectors() before any journal/mode check:
> 
>   if (ic->sb->flags & cpu_to_le32(SB_FLAG_DIRTY_BITMAP)) {
>       rw_journal_sectors(ic, REQ_OP_READ, ...);  /* uses ic->journal[] */
> 
> rw_journal_sectors() then passes that NULL page list into dm_io():
> 
>   io_req.mem.type = DM_IO_PAGE_LIST;
>   io_req.mem.ptr.pl = &ic->journal[pl_index];  /* NULL in mode R */
> 
> list_get_page() does *p = pl->page with pl == NULL (KASAN range [0x8-0xf]).
> 
> DIRTY_BITMAP is set while bitmap mode (B) is active and is cleared on a
> clean postsuspend. It remains on disk after an unclean stop of mode B
> (crash / power loss). Reloading that device in recovery mode R is a
> documented recovery path and hits this bug.
> 
> Affected
> ========
> 
> - Confirmed on Linux 6.6.144 (da47cbc254661aa66d61ef061485a7080305c4be),
>   KASAN guest
> - Still present on torvalds/linux master as of 2026-08-17: resume still
>   calls rw_journal_sectors() under DIRTY_BITMAP with no journal / mode-R
>   guard
> - Files: drivers/md/dm-integrity.c
> - Config: CONFIG_DM=y, CONFIG_DM_INTEGRITY=y (KASAN for the report)
> 
> Crash excerpt (from minimized PoC)
> ==================================
> 
> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> CPU: 0 PID: 234 Comm: repro Not tainted 6.6.144 #15
> RIP: 0010:list_get_page+0x7e/0x150
> Call Trace:
>  <TASK>
>   dispatch_io
>   sync_io
>   dm_io
>   rw_journal_sectors
>   dm_integrity_resume
>   dm_table_resume_targets
>   __dm_resume
>   dm_resume
>   dev_suspend
>   ctl_ioctl
>   dm_ctl_ioctl
>   __x64_sys_ioctl
>  </TASK>
> Kernel panic - not syncing: Fatal exception
> 
> Full oops and a self-contained Docker/QEMU reproducer (poc.c + KASAN
> guest) are available on request.
> 
> I am happy to test patches or send the reproducer package.
> 
> Thanks,
> Yu Junzhe
> FuzzAnything <[email protected]>

Hi

Does this patch fix it?

Mikulas


dm-integrity: fix NULL pointer dereference when the 'R' flag is used

If the dm-integrity device has the SB_FLAG_DIRTY_BITMAP flag set and the
user activates the device in the 'R' mode, a crash in dm_integrity_resume
happens because the function attempts to read the journal containing the
bitmap.

This patch makes dm-integrity skip any writes to the device in
dm_integrity_resume if the device is activated in the 'R' mode.

Signed-off-by: Mikulas Patocka <[email protected]>
Cc: [email protected]

---
 drivers/md/dm-integrity.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: linux-2.6/drivers/md/dm-integrity.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-integrity.c	2026-08-10 14:00:08.000000000 +0200
+++ linux-2.6/drivers/md/dm-integrity.c	2026-08-17 17:01:02.000000000 +0200
@@ -3875,6 +3875,10 @@ static void dm_integrity_resume(struct d
 	r = sync_rw_sb(ic, REQ_OP_READ);
 	if (r)
 		dm_integrity_io_error(ic, "reading superblock", r);
+
+	if (ic->mode == 'R')
+		goto skip_writes;
+
 	if ((ic->sb->flags & flags) != flags) {
 		ic->sb->flags |= flags;
 		r = sync_rw_sb(ic, REQ_OP_WRITE | REQ_FUA);
@@ -3984,6 +3988,7 @@ static void dm_integrity_resume(struct d
 		}
 	}
 
+skip_writes:
 	ic->reboot_notifier.notifier_call = dm_integrity_reboot;
 	ic->reboot_notifier.next = NULL;
 	ic->reboot_notifier.priority = INT_MAX - 1;	/* be notified after md and before hardware drivers */