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authorMiklos Szeredi <mszeredi@suse.cz>2014-10-24 00:14:39 +0200
committerMiklos Szeredi <mszeredi@suse.cz>2014-10-24 00:14:39 +0200
commit69c433ed2ecd2d3264efd7afec4439524b319121 (patch)
tree49fcf55fbd3913881ccb47a6e700f668a4307daf
parent7c37fbda85ceb9be7bdb9d5f53e702efc40cf783 (diff)
downloadlinux-69c433ed2ecd2d3264efd7afec4439524b319121.tar.bz2
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. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
-rw-r--r--fs/ecryptfs/main.c7
-rw-r--r--fs/overlayfs/super.c9
-rw-r--r--include/linux/fs.h11
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);