[PATCH] dm crypt: fix use of uninitialized percpu_counter in ctr error path

[Zhao Feng]

If percpu_counter_init() fails in crypt_ctr() (e.g. when the
underlying percpu allocation fails under memory pressure or fault
injection), the error path jumps to "bad", which calls
crypt_dtr().  crypt_dtr() then evaluates
WARN_ON(percpu_counter_sum(&cc->n_allocated_pages) != 0) and calls
percpu_counter_destroy() on a counter that was never initialized,
because __percpu_counter_init_many() returns -ENOMEM before
calling raw_spin_lock_init() on fbc->lock.

With lockdep enabled this triggers "INFO: trying to register
non-static key" in __percpu_counter_sum(), as reported by syzbot.
The console additionally shows "crypt: Unknown error (-ENOMEM)"
because this failure path sets no ti->error.

Move percpu_counter_init() to right after the allocation of cc,
before ti->private is set and before any "goto bad" can happen.
On failure, set ti->error and free cc directly, so that
crypt_dtr() is only ever called with an initialized counter.

Reported-by: syzbot+4b232570d625662eaab4@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzbot.org/bug?extid=4b232570d625662eaab4
Fixes: 5059353df86e ("dm crypt: limit the number of allocated pages")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Zhao Feng <zhaofeng2@xxxxxxxxxxxxxxxxxxxx>
---
Not runtime-tested (the syzbot report has no reproducer; the
failure requires percpu_counter_init() to fail).  The affected
crypt_ctr() code is identical in current upstream master, so the
patch applies there as-is.  The Fixes hash was verified against
the upstream commit that introduced both the init call in
crypt_ctr() and the teardown in crypt_dtr().

 drivers/md/dm-crypt.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 1ff16b8264..3e69dcc366 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -3249,6 +3249,14 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		ti->error = "Cannot allocate encryption context";
 		return -ENOMEM;
 	}
+
+	ret = percpu_counter_init(&cc->n_allocated_pages, 0, GFP_KERNEL);
+	if (ret < 0) {
+		ti->error = "Cannot initialize page counter";
+		kfree_sensitive(cc);
+		return ret;
+	}
+
 	cc->key_size = key_size;
 	cc->sector_size = (1 << SECTOR_SHIFT);
 	cc->sector_shift = 0;
@@ -3260,10 +3268,6 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	crypt_calculate_pages_per_client();
 	spin_unlock(&dm_crypt_clients_lock);
 
-	ret = percpu_counter_init(&cc->n_allocated_pages, 0, GFP_KERNEL);
-	if (ret < 0)
-		goto bad;
-
 	/* Optional parameters need to be read before cipher constructor */
 	if (argc > 5) {
 		ret = crypt_ctr_optional(ti, argc - 5, &argv[5]);
-- 
2.39.2