From 69c433ed2ecd2d3264efd7afec4439524b319121 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Fri, 24 Oct 2014 00:14:39 +0200 Subject: 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 --- fs/overlayfs/super.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'fs/overlayfs/super.c') 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)) { -- cgit v1.2.3