fs: limit filesystem stacking depth

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.

Miklos Szeredi committed 12 years ago

Commit 69c433e1 parent 7c37fbd3 files · +27 −0Browse files

Unified · Split

3 files

fs/ecryptfs/main.c +7 −0
fs/overlayfs/super.c +9 −0
include/linux/fs.h +11 −0

fs/ecryptfs/main.c+7−0

@@ -566,6 +566,13 @@ static struct dentry ecryptfs_mount(struct file_system_type fs_type, int flags · 565 unmodified lines
566	566	s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
567	567	s->s_blocksize = path.dentry->d_sb->s_blocksize;
568	568	s->s_magic = ECRYPTFS_SUPER_MAGIC;
	569	+ s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1;
	570	+
	571	+ rc = -EINVAL;
	572	+ if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
	573	+ pr_err("eCryptfs: maximum fs stacking depth exceeded\n");
	574	+ goto out_free;
	575	+ }
569	576
570	577	inode = ecryptfs_get_inode(path.dentry->d_inode, s);
571	578	rc = PTR_ERR(inode);

fs/overlayfs/super.c+9−0

@@ -677,6 +677,15 @@ static int ovl_fill_super(struct super_block sb, void data, int silent) · 676 unmodified lines
677	677	}
678	678	ufs->lower_namelen = statfs.f_namelen;
679	679
	680	+ sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
	681	+ lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
	682	+
	683	+ err = -EINVAL;
	684	+ if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
	685	+ pr_err("overlayfs: maximum fs stacking depth exceeded\n");
	686	+ goto out_put_workpath;
	687	+ }
	688	+
680	689	ufs->upper_mnt = clone_private_mount(&upperpath);
681	690	err = PTR_ERR(ufs->upper_mnt);
682	691	if (IS_ERR(ufs->upper_mnt)) {

include/linux/fs.h+11−0

@@ -261,6 +261,12 @@ struct iattr { · 260 unmodified lines
261	261	*/
262	262	#include <linux/quota.h>
263	263
	264	+/*
	265	+ * Maximum number of layers of fs stack. Needs to be limited to
	266	+ * prevent kernel stack overflow
	267	+ */
	268	+#define FILESYSTEM_MAX_STACK_DEPTH 2
	269	+
264	270	/**
265	271	* enum positive_aop_returns - aop return codes with specific semantics
266	272	*
@@ -1273,6 +1279,11 @@ struct super_block { · 1006 unmodified lines
1273	1279	struct list_lru s_dentry_lru ____cacheline_aligned_in_smp;
1274	1280	struct list_lru s_inode_lru ____cacheline_aligned_in_smp;
1275	1281	struct rcu_head rcu;
	1282	+
	1283	+ /*
	1284	+ * Indicates how deep in a filesystem stack this SB is
	1285	+ */
	1286	+ int s_stack_depth;
1276	1287	};
1277	1288
1278	1289	extern struct timespec current_fs_time(struct super_block *sb);