dm-integrity: Avoid divide by zero in table status in Inline mode

JIRA: https://issues.redhat.com/browse/RHEL-84777
Upstream Status: kernel/git/torvalds/linux.git

commit 7fb3988
Author: Milan Broz <gmazyland@gmail.com>
Date:   Sun Feb 16 11:42:09 2025 +0100

    dm-integrity: Avoid divide by zero in table status in Inline mode

    In Inline mode, the journal is unused, and journal_sectors is zero.

    Calculating the journal watermark requires dividing by journal_sectors,
    which should be done only if the journal is configured.

    Otherwise, a simple table query (dmsetup table) can cause OOPS.

    This bug did not show on some systems, perhaps only due to
    compiler optimization.

    On my 32-bit testing machine, this reliably crashes with the following:

     : Oops: divide error: 0000 [#1] PREEMPT SMP
     : CPU: 0 UID: 0 PID: 2450 Comm: dmsetup Not tainted 6.14.0-rc2+ #959
     : EIP: dm_integrity_status+0x2f8/0xab0 [dm_integrity]
     ...

    Signed-off-by: Milan Broz <gmazyland@gmail.com>
    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
    Fixes: fb09876 ("dm-integrity: introduce the Inline mode")
    Cc: stable@vger.kernel.org # 6.11+

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>

Author: bmarzins

drivers/md/dm-integrity.c

@@ -3790,10 +3790,6 @@ static void dm_integrity_status(struct dm_target *ti, status_type_t type,
 		break;
 
 	case STATUSTYPE_TABLE: {
-		__u64 watermark_percentage = (__u64)(ic->journal_entries - ic->free_sectors_threshold) * 100;
-
-		watermark_percentage += ic->journal_entries / 2;
-		do_div(watermark_percentage, ic->journal_entries);
 		arg_count = 3;
 		arg_count += !!ic->meta_dev;
 		arg_count += ic->sectors_per_block != 1;
@@ -3826,6 +3822,10 @@ static void dm_integrity_status(struct dm_target *ti, status_type_t type,
 		DMEMIT(" interleave_sectors:%u", 1U << ic->sb->log2_interleave_sectors);
 		DMEMIT(" buffer_sectors:%u", 1U << ic->log2_buffer_sectors);
 		if (ic->mode == 'J') {
+			__u64 watermark_percentage = (__u64)(ic->journal_entries - ic->free_sectors_threshold) * 100;
+
+			watermark_percentage += ic->journal_entries / 2;
+			do_div(watermark_percentage, ic->journal_entries);
 			DMEMIT(" journal_watermark:%u", (unsigned int)watermark_percentage);
 			DMEMIT(" commit_time:%u", ic->autocommit_msec);
 		}