95 lines
2.8 KiB
Diff
95 lines
2.8 KiB
Diff
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From 094e2fc56d5a0dd9d5c579e08bd4df3013bb171a Mon Sep 17 00:00:00 2001
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From: Miklos Szeredi <mszeredi@suse.cz>
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Date: Thu, 27 Jun 2013 16:39:50 +0200
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Subject: [PATCH 9/9] fs: limit filesystem stacking depth
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Add a simple read-only counter to super_block that indicates deep this
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is in the stack of filesystems. Previously ecryptfs was the only
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stackable filesystem and it explicitly disallowed multiple layers of
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itself.
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Overlayfs, however, can be stacked recursively and also may be stacked
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on top of ecryptfs or vice versa.
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To limit the kernel stack usage we must limit the depth of the
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filesystem stack. Initially the limit is set to 2.
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Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
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---
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fs/ecryptfs/main.c | 7 +++++++
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fs/overlayfs/super.c | 10 ++++++++++
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include/linux/fs.h | 11 +++++++++++
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3 files changed, 28 insertions(+)
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diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
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index e924cf4..8b0957e 100644
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--- a/fs/ecryptfs/main.c
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+++ b/fs/ecryptfs/main.c
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@@ -567,6 +567,13 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
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s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
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s->s_blocksize = path.dentry->d_sb->s_blocksize;
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s->s_magic = ECRYPTFS_SUPER_MAGIC;
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+ s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1;
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+
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+ rc = -EINVAL;
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+ if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
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+ pr_err("eCryptfs: maximum fs stacking depth exceeded\n");
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+ goto out_free;
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+ }
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inode = ecryptfs_get_inode(path.dentry->d_inode, s);
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rc = PTR_ERR(inode);
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diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
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index 066ea5a..9473e79 100644
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--- a/fs/overlayfs/super.c
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+++ b/fs/overlayfs/super.c
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@@ -570,6 +570,16 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
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}
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ufs->lower_namelen = statfs.f_namelen;
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+ sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
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+ lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
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+
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+ err = -EINVAL;
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+ if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
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+ pr_err("overlayfs: maximum fs stacking depth exceeded\n");
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+ goto out_put_lowerpath;
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+ }
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+
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+
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ufs->upper_mnt = clone_private_mount(&upperpath);
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err = PTR_ERR(ufs->upper_mnt);
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if (IS_ERR(ufs->upper_mnt)) {
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diff --git a/include/linux/fs.h b/include/linux/fs.h
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index 8a6752b..72d04f8 100644
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--- a/include/linux/fs.h
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+++ b/include/linux/fs.h
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@@ -244,6 +244,12 @@ struct iattr {
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*/
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#include <linux/quota.h>
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+/*
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+ * Maximum number of layers of fs stack. Needs to be limited to
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+ * prevent kernel stack overflow
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+ */
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+#define FILESYSTEM_MAX_STACK_DEPTH 2
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+
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/**
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* enum positive_aop_returns - aop return codes with specific semantics
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*
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@@ -1322,6 +1328,11 @@ struct super_block {
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/* Being remounted read-only */
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int s_readonly_remount;
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+
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+ /*
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+ * Indicates how deep in a filesystem stack this SB is
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+ */
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+ int s_stack_depth;
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};
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/* superblock cache pruning functions */
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--
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1.8.3.2
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