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mtd: key superblock by device number

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The mtd driver has similar problems than the one that was fixed in
commit dc3216b141 ("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
Acked-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Message-Id: <20230829-vfs-super-mtd-v1-2-fecb572e5df3@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2023-08-29 17:23:57 +02:00
parent 69881be3d9
commit ec952aa253
1 changed files with 11 additions and 34 deletions
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45
drivers/mtd/mtdsuper.c
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@ -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;