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fs: limit filesystem stacking depth

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commit 69c433ed2ecd2d3264efd7afec4439524b319121 upstream.

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.

Change-Id: I2659379e1ba70d1f41290d378b6a032b0b4cdd23
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
[bwh: Backported to 3.2:
 - Drop changes to overlayfs
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Miklos Szeredi 2014-10-24 00:14:39 +02:00 committed by syphyr
parent 1a5e2bdeee
commit 45a46387b4
1 changed files with 7 additions and 0 deletions
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7
fs/ecryptfs/main.c
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@ -577,6 +577,13 @@ 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);