linux-kernel - [PATCH 5.5 185/257] dm clone: Add overflow check for number of regions

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Message-Id: <20200416131349.450708706@linuxfoundation.org>
Date:   Thu, 16 Apr 2020 15:23:56 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nikos Tsironis <ntsironis@...ikto.com>,
        Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 5.5 185/257] dm clone: Add overflow check for number of regions

From: Nikos Tsironis <ntsironis@...ikto.com>

commit cd481c12269b4d276f1a52eda0ebd419079bfe3a upstream.

Add overflow check for clone->nr_regions variable, which holds the
number of regions of the target.

The overflow can occur with sufficiently large devices, if BITS_PER_LONG
== 32. E.g., if the region size is 8 sectors (4K), the overflow would
occur for device sizes > 34359738360 sectors (~16TB).

This could result in multiple device sectors wrongly mapping to the same
region number, due to the truncation from 64 bits to 32 bits, which
would lead to data corruption.

Fixes: 7431b7835f55 ("dm: add clone target")
Cc: stable@...r.kernel.org # v5.4+
Signed-off-by: Nikos Tsironis <ntsironis@...ikto.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/dm-clone-target.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/md/dm-clone-target.c
+++ b/drivers/md/dm-clone-target.c
@@ -1790,6 +1790,7 @@ error:
 static int clone_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 {
 	int r;
+	sector_t nr_regions;
 	struct clone *clone;
 	struct dm_arg_set as;
 
@@ -1831,7 +1832,16 @@ static int clone_ctr(struct dm_target *t
 		goto out_with_source_dev;
 
 	clone->region_shift = __ffs(clone->region_size);
-	clone->nr_regions = dm_sector_div_up(ti->len, clone->region_size);
+	nr_regions = dm_sector_div_up(ti->len, clone->region_size);
+
+	/* Check for overflow */
+	if (nr_regions != (unsigned long)nr_regions) {
+		ti->error = "Too many regions. Consider increasing the region size";
+		r = -EOVERFLOW;
+		goto out_with_source_dev;
+	}
+
+	clone->nr_regions = nr_regions;
 
 	r = validate_nr_regions(clone->nr_regions, &ti->error);
 	if (r)