[dm-devel] [PATCH 1/2] dm table: fix invalid memory accesses with too high sector number

[Mikulas Patocka]

If the sector number is too high, dm_table_find_target should return a
pointer to a zeroed dm_target structure (the caller should test it with
dm_target_is_valid).

However, for some table sizes, the code in dm_table_find_target that
performs btree lookup will access out of bound memory structures.

This patch fixes the bug by testing the sector number at the beginning of
dm_table_find_target. We add an "inline" keyword to the function
dm_table_get_size because this is hot path.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
Reported-by: Zhang Tao <kontais at zoho.com>
Fixes: 512875bd9661 ("dm: table detect io beyond device")
Cc: stable at vger.kernel.org

---
 drivers/md/dm-table.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: linux-2.6/drivers/md/dm-table.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-table.c	2019-08-23 13:40:51.000000000 +0200
+++ linux-2.6/drivers/md/dm-table.c	2019-08-23 15:43:19.000000000 +0200
@@ -1342,7 +1342,7 @@ void dm_table_event(struct dm_table *t)
 }
 EXPORT_SYMBOL(dm_table_event);
 
-sector_t dm_table_get_size(struct dm_table *t)
+inline sector_t dm_table_get_size(struct dm_table *t)
 {
 	return t->num_targets ? (t->highs[t->num_targets - 1] + 1) : 0;
 }
@@ -1367,6 +1367,9 @@ struct dm_target *dm_table_find_target(s
 	unsigned int l, n = 0, k = 0;
 	sector_t *node;
 
+	if (unlikely(sector >= dm_table_get_size(t)))
+		return &t->targets[t->num_targets];
+
 	for (l = 0; l < t->depth; l++) {
 		n = get_child(n, k);
 		node = get_node(t, l, n);