[PATCH 1/2] dm era: fix NULL pointer dereference in metadata_open()

[ghuicao]

From: Cao Guanghui <caoguanghui@xxxxxxxxxx>

metadata_open() returns NULL when kzalloc_obj() fails, but the
caller era_ctr() only checks IS_ERR(md).  Since IS_ERR(NULL)
returns false, the NULL pointer is treated as a valid result
and later assigned to era->md, leading to a NULL pointer
dereference when the metadata is accessed.

Fix this by returning ERR_PTR(-ENOMEM) on allocation failure,
consistent with dm-cache-metadata.c, dm-thin-metadata.c, and
dm-clone-metadata.c which all use ERR_PTR(-ENOMEM) for the
same pattern.

Fixes: eec40579d848 ("dm: add era target")
Signed-off-by: Cao Guanghui <caoguanghui@xxxxxxxxxx>
---
 drivers/md/dm-era-target.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-era-target.c b/drivers/md/dm-era-target.c
index 05285c04ff2c..08ce96e8cf4f 100644
--- a/drivers/md/dm-era-target.c
+++ b/drivers/md/dm-era-target.c
@@ -810,8 +810,10 @@ static struct era_metadata *metadata_open(struct block_device *bdev,
 	int r;
 	struct era_metadata *md = kzalloc_obj(*md);
 
-	if (!md)
-		return NULL;
+	if (!md) {
+		DMERR("could not allocate metadata struct");
+		return ERR_PTR(-ENOMEM);
+	}
 
 	md->bdev = bdev;
 	md->block_size = block_size;
-- 
2.25.1