[PATCH v3 3/7] mtd: Check permissions towards mtd block device inode when mounting

From: Seth Forshee
Date: Tue Nov 17 2015 - 11:42:17 EST

Unprivileged users should not be able to mount mtd block devices
when they lack sufficient privileges towards the block device
inode. Update mount_mtd() to validate that the user has the
required access to the inode at the specified path. The check
will be skipped for CAP_SYS_ADMIN, so privileged mounts will
continue working as before.

Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
drivers/mtd/mtdsuper.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c
index b5b60e1af31c..5d7e7705fed8 100644
--- a/drivers/mtd/mtdsuper.c
+++ b/drivers/mtd/mtdsuper.c
@@ -125,6 +125,7 @@ struct dentry *mount_mtd(struct file_system_type *fs_type, int flags,
struct block_device *bdev;
int ret, major;
+ int perm;
int mtdnr;

@@ -176,7 +177,10 @@ struct dentry *mount_mtd(struct file_system_type *fs_type, int flags,
/* try the old way - the hack where we allowed users to mount
* /dev/mtdblock$(n) but didn't actually _use_ the blockdev
- bdev = lookup_bdev(dev_name, 0);
+ perm = MAY_READ;
+ if (!(flags & MS_RDONLY))
+ perm |= MAY_WRITE;
+ bdev = lookup_bdev(dev_name, perm);
if (IS_ERR(bdev)) {
ret = PTR_ERR(bdev);
pr_debug("MTDSB: lookup_bdev() returned %d\n", ret);

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