[PATCH 5.10.y] dm-verity: make error counter atomic

[Sasha Levin <sashal@kernel.org>]

From: Mikulas Patocka <mpatocka@redhat.com>

[ Upstream commit 8ec4d9c5a5cf4b61fc087f871465b1f79b393325 ]

The error counter "v->corrupted_errs" was not atomic, thus it could be
subject to race conditions. The call to
dm_audit_log_target("max-corrupted-errors") may be skipped due to the
races.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Assisted-by: Claude:claude-opus-4.6
Fixes: 65ff5b7ddf05 ("dm verity: add error handling modes for corrupted blocks")
Cc: stable@vger.kernel.org
[ kept 5.15's braceless single-statement DMERR body instead of upstream's braced block containing the absent dm_audit_log_target() call ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/dm-verity-target.c | 12 +++++++-----
 drivers/md/dm-verity.h        |  2 +-
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 21ef7168cc0b04..926a8c990163b3 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -217,14 +217,16 @@ static int verity_handle_err(struct dm_verity *v, enum verity_block_type type,
 	char *envp[] = { verity_env, NULL };
 	const char *type_str = "";
 	struct mapped_device *md = dm_table_get_md(v->ti->table);
+	int ce;
 
 	/* Corruption should be visible in device status in all modes */
 	v->hash_failed = 1;
 
-	if (v->corrupted_errs >= DM_VERITY_MAX_CORRUPTED_ERRS)
-		goto out;
-
-	v->corrupted_errs++;
+	ce = atomic_read(&v->corrupted_errs);
+	do {
+		if (ce >= DM_VERITY_MAX_CORRUPTED_ERRS)
+			goto out;
+	} while (!atomic_try_cmpxchg(&v->corrupted_errs, &ce, ce + 1));
 
 	switch (type) {
 	case DM_VERITY_BLOCK_TYPE_DATA:
@@ -240,7 +242,7 @@ static int verity_handle_err(struct dm_verity *v, enum verity_block_type type,
 	DMERR_LIMIT("%s: %s block %llu is corrupted", v->data_dev->name,
 		    type_str, block);
 
-	if (v->corrupted_errs == DM_VERITY_MAX_CORRUPTED_ERRS)
+	if (ce + 1 == DM_VERITY_MAX_CORRUPTED_ERRS)
 		DMERR("%s: reached maximum errors", v->data_dev->name);
 
 	snprintf(verity_env, DM_VERITY_ENV_LENGTH, "%s=%d,%llu",
diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
index f61c89c79cf5b9..ad5104daddb54a 100644
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -55,7 +55,7 @@ struct dm_verity {
 	unsigned int ahash_reqsize;/* the size of temporary space for crypto */
 	int hash_failed;	/* set to 1 if hash of any block failed */
 	enum verity_mode mode;	/* mode for handling verification errors */
-	unsigned corrupted_errs;/* Number of errors for corrupted blocks */
+	atomic_t corrupted_errs;/* Number of errors for corrupted blocks */
 
 	struct workqueue_struct *verify_wq;
 
-- 
2.53.0