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fs: limit filesystem stacking depth

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Add a simple read-only counter to super_block that indicates how deep this
is in the stack of filesystems.  Previously ecryptfs was the only stackable
filesystem and it explicitly disallowed multiple layers of itself.

Overlayfs, however, can be stacked recursively and also may be stacked
on top of ecryptfs or vice versa.

To limit the kernel stack usage we must limit the depth of the
filesystem stack.  Initially the limit is set to 2.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
This commit is contained in:
Miklos Szeredi
2014-10-24 00:14:39 +02:00
parent 7c37fbda85
commit 69c433ed2e
3 changed files with 27 additions and 0 deletions
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fs/ecryptfs/main.c
+7
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@@ -566,6 +566,13 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
s->s_blocksize = path.dentry->d_sb->s_blocksize;
s->s_magic = ECRYPTFS_SUPER_MAGIC;
s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1;
rc = -EINVAL;
if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
pr_err("eCryptfs: maximum fs stacking depth exceeded\n");
goto out_free;
}
inode = ecryptfs_get_inode(path.dentry->d_inode, s);
rc = PTR_ERR(inode);