The mtd driver has similar problems than the one that was fixed in
commit dc3216b14160 ("super: ensure valid info").
The kill_mtd_super() helper calls shuts the superblock down but leaves
the superblock on fs_supers as the devices are still in use but puts the
mtd device and cleans out the superblock's s_mtd field.
This means another mounter can find the superblock on the list accessing
its s_mtd field while it is curently in the process of being freed or
already freed.
Prevent that from happening by keying superblock by dev_t just as we do
in the generic code.
Link: https://lore.kernel.org/linux-fsdevel/20230829-weitab-lauwarm-49c40fc85863@brauner
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
drivers/mtd/mtdsuper.c | 45 +++++++++++----------------------------------
1 file changed, 11 insertions(+), 34 deletions(-)
diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c
index 5ff001140ef4..b7e3763c47f0 100644
--- a/drivers/mtd/mtdsuper.c
+++ b/drivers/mtd/mtdsuper.c
@@ -19,38 +19,6 @@
#include <linux/fs_context.h>
#include "mtdcore.h"
-/*
- * compare superblocks to see if they're equivalent
- * - they are if the underlying MTD device is the same
- */
-static int mtd_test_super(struct super_block *sb, struct fs_context *fc)
-{
- struct mtd_info *mtd = fc->sget_key;
-
- if (sb->s_mtd == fc->sget_key) {
- pr_debug("MTDSB: Match on device %d (\"%s\")\n",
- mtd->index, mtd->name);
- return 1;
- }
-
- pr_debug("MTDSB: No match, device %d (\"%s\"), device %d (\"%s\")\n",
- sb->s_mtd->index, sb->s_mtd->name, mtd->index, mtd->name);
- return 0;
-}
-
-/*
- * mark the superblock by the MTD device it is using
- * - set the device number to be the correct MTD block device for pesuperstence
- * of NFS exports
- */
-static int mtd_set_super(struct super_block *sb, struct fs_context *fc)
-{
- sb->s_mtd = fc->sget_key;
- sb->s_dev = MKDEV(MTD_BLOCK_MAJOR, sb->s_mtd->index);
- sb->s_bdi = bdi_get(mtd_bdi);
- return 0;
-}
-
/*
* get a superblock on an MTD-backed filesystem
*/
@@ -62,8 +30,7 @@ static int mtd_get_sb(struct fs_context *fc,
struct super_block *sb;
int ret;
- fc->sget_key = mtd;
- sb = sget_fc(fc, mtd_test_super, mtd_set_super);
+ sb = sget_dev(fc, MKDEV(MTD_BLOCK_MAJOR, mtd->index));
if (IS_ERR(sb))
return PTR_ERR(sb);
@@ -77,6 +44,16 @@ static int mtd_get_sb(struct fs_context *fc,
pr_debug("MTDSB: New superblock for device %d (\"%s\")\n",
mtd->index, mtd->name);
+ /*
+ * Would usually have been set with @sb_lock held but in
+ * contrast to sb->s_bdev that's checked with only
+ * @sb_lock held, nothing checks sb->s_mtd without also
+ * holding sb->s_umount and we're holding sb->s_umount
+ * here.
+ */
+ sb->s_mtd = mtd;
+ sb->s_bdi = bdi_get(mtd_bdi);
+
ret = fill_super(sb, fc);
if (ret < 0)
goto error_sb;
--
2.34.1
