From: Seth Forshee <seth.forshee@xxxxxxxxxxxxx> When looking up a block device by path no permission check is done to verify that the user has access to the block device inode at the specified path. In some cases it may be necessary to check permissions towards the inode, such as allowing unprivileged users to mount block devices in user namespaces. Add an argument to lookup_bdev() to optionally perform this permission check. A value of 0 skips the permission check and behaves the same as before. A non-zero value specifies the mask of access rights required towards the inode at the specified path. The check is always skipped if the user has CAP_SYS_ADMIN. All callers of lookup_bdev() currently pass a mask of 0, so this patch results in no functional change. Subsequent patches will add permission checks where appropriate. Patch v4 is available: https://patchwork.kernel.org/patch/8943601/ Cc: dm-devel@xxxxxxxxxx Cc: linux-bcache@xxxxxxxxxxxxxxx Cc: linux-fsdevel@xxxxxxxxxxxxxxx Cc: linux-mtd@xxxxxxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Jan Kara <jack@xxxxxxxx> Cc: Serge Hallyn <serge@xxxxxxxxxx> Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx> Signed-off-by: Dongsu Park <dongsu@xxxxxxxxxx> --- drivers/md/bcache/super.c | 2 +- drivers/md/dm-table.c | 2 +- drivers/mtd/mtdsuper.c | 2 +- fs/block_dev.c | 13 ++++++++++--- fs/quota/quota.c | 2 +- include/linux/fs.h | 2 +- 6 files changed, 15 insertions(+), 8 deletions(-) diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index b4d28928..acc9d56c 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -1967,7 +1967,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr, sb); if (IS_ERR(bdev)) { if (bdev == ERR_PTR(-EBUSY)) { - bdev = lookup_bdev(strim(path)); + bdev = lookup_bdev(strim(path), 0); mutex_lock(&bch_register_lock); if (!IS_ERR(bdev) && bch_is_open(bdev)) err = "device already registered"; diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c index 88130b5d..bca5eaf4 100644 --- a/drivers/md/dm-table.c +++ b/drivers/md/dm-table.c @@ -410,7 +410,7 @@ dev_t dm_get_dev_t(const char *path) dev_t dev; struct block_device *bdev; - bdev = lookup_bdev(path); + bdev = lookup_bdev(path, 0); if (IS_ERR(bdev)) dev = name_to_dev_t(path); else { diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c index e43fea89..4a4d40c0 100644 --- a/drivers/mtd/mtdsuper.c +++ b/drivers/mtd/mtdsuper.c @@ -180,7 +180,7 @@ 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); + bdev = lookup_bdev(dev_name, 0); if (IS_ERR(bdev)) { ret = PTR_ERR(bdev); pr_debug("MTDSB: lookup_bdev() returned %d\n", ret); diff --git a/fs/block_dev.c b/fs/block_dev.c index 4a181fcb..5ca06095 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -1662,7 +1662,7 @@ struct block_device *blkdev_get_by_path(const char *path, fmode_t mode, struct block_device *bdev; int err; - bdev = lookup_bdev(path); + bdev = lookup_bdev(path, 0); if (IS_ERR(bdev)) return bdev; @@ -2052,12 +2052,14 @@ EXPORT_SYMBOL(ioctl_by_bdev); /** * lookup_bdev - lookup a struct block_device by name * @pathname: special file representing the block device + * @mask: rights to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC) * * Get a reference to the blockdevice at @pathname in the current * namespace if possible and return it. Return ERR_PTR(error) - * otherwise. + * otherwise. If @mask is non-zero, check for access rights to the + * inode at @pathname. */ -struct block_device *lookup_bdev(const char *pathname) +struct block_device *lookup_bdev(const char *pathname, int mask) { struct block_device *bdev; struct inode *inode; @@ -2072,6 +2074,11 @@ struct block_device *lookup_bdev(const char *pathname) return ERR_PTR(error); inode = d_backing_inode(path.dentry); + if (mask != 0 && !capable(CAP_SYS_ADMIN)) { + error = __inode_permission(inode, mask); + if (error) + goto fail; + } error = -ENOTBLK; if (!S_ISBLK(inode->i_mode)) goto fail; diff --git a/fs/quota/quota.c b/fs/quota/quota.c index 43612e2a..e5d47955 100644 --- a/fs/quota/quota.c +++ b/fs/quota/quota.c @@ -807,7 +807,7 @@ static struct super_block *quotactl_block(const char __user *special, int cmd) if (IS_ERR(tmp)) return ERR_CAST(tmp); - bdev = lookup_bdev(tmp->name); + bdev = lookup_bdev(tmp->name, 0); putname(tmp); if (IS_ERR(bdev)) return ERR_CAST(bdev); diff --git a/include/linux/fs.h b/include/linux/fs.h index 2995a271..fce19c49 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2551,7 +2551,7 @@ static inline void unregister_chrdev(unsigned int major, const char *name) #define BLKDEV_MAJOR_MAX 512 extern const char *__bdevname(dev_t, char *buffer); extern const char *bdevname(struct block_device *bdev, char *buffer); -extern struct block_device *lookup_bdev(const char *); +extern struct block_device *lookup_bdev(const char *, int mask); extern void blkdev_show(struct seq_file *,off_t); #else -- 2.13.6 -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
