3 files changed, 27 insertions, 0 deletions

diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index 1b119d3bf924..c4cd1fd86cc2 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -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);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 7dcc24e84417..08b704cebfc4 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -677,6 +677,15 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
         }
         ufs->lower_namelen = statfs.f_namelen;
 
+        sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
+                                lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
+
+        err = -EINVAL;
+        if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
+                pr_err("overlayfs: maximum fs stacking depth exceeded\n");
+                goto out_put_workpath;
+        }
+
         ufs->upper_mnt = clone_private_mount(&upperpath);
         err = PTR_ERR(ufs->upper_mnt);
         if (IS_ERR(ufs->upper_mnt)) {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 69118b3cb917..4e41a4a331bb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -261,6 +261,12 @@ struct iattr {
  */
 #include <linux/quota.h>
 
+/*
+ * Maximum number of layers of fs stack.  Needs to be limited to
+ * prevent kernel stack overflow
+ */
+#define FILESYSTEM_MAX_STACK_DEPTH 2
+
 /** 
  * enum positive_aop_returns - aop return codes with specific semantics
  *
@@ -1273,6 +1279,11 @@ struct super_block {
         struct list_lru         s_dentry_lru ____cacheline_aligned_in_smp;
         struct list_lru         s_inode_lru ____cacheline_aligned_in_smp;
         struct rcu_head         rcu;
+
+        /*
+         * Indicates how deep in a filesystem stack this SB is
+         */
+        int s_stack_depth;
 };
 
 extern struct timespec current_fs_time(struct super_block *sb);