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From 1ef45eb31cacd58c4c62e1fd26aa63a1f3d031a7 Mon Sep 17 00:00:00 2001
From: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
Date: Thu, 29 Sep 2016 15:11:15 +0200
Subject: [PATCH] Add printk-based debugging to pivot_root
This patch changes pivot_root to make it obvious which error exit path
was taken. It might be useful to apply to debug and investigate how
undocumented requirements of pivot_root are not met.
Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
---
fs/namespace.c | 70 ++++++++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 53 insertions(+), 17 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 877fc2c..6e15d1d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2993,57 +2993,93 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
return -EPERM;
error = user_path_dir(new_root, &new);
- if (error)
+ if (error) {
+ printk(KERN_ERR "user_path_dir(new_root, &new) returned an error\n");
goto out0;
+ }
error = user_path_dir(put_old, &old);
- if (error)
+ if (error) {
+ printk(KERN_ERR "user_path_dir(put_old, &old) returned an error\n");
goto out1;
+ }
error = security_sb_pivotroot(&old, &new);
- if (error)
+ if (error) {
+ printk(KERN_ERR "security_sb_pivotroot(&old, &new) returned an error\n");
goto out2;
+ }
get_fs_root(current->fs, &root);
old_mp = lock_mount(&old);
error = PTR_ERR(old_mp);
- if (IS_ERR(old_mp))
+ if (IS_ERR(old_mp)) {
+ printk(KERN_ERR "IS_ERR(old_mp)\n");
goto out3;
+ }
error = -EINVAL;
new_mnt = real_mount(new.mnt);
root_mnt = real_mount(root.mnt);
old_mnt = real_mount(old.mnt);
- if (IS_MNT_SHARED(old_mnt) ||
- IS_MNT_SHARED(new_mnt->mnt_parent) ||
- IS_MNT_SHARED(root_mnt->mnt_parent))
+ if (IS_MNT_SHARED(old_mnt)) {
+ printk(KERN_ERR "IS_MNT_SHARED(old_mnt)\n");
+ goto out4;
+ }
+ if (IS_MNT_SHARED(new_mnt->mnt_parent)) {
+ printk(KERN_ERR "IS_MNT_SHARED(new_mnt->mnt_parent)\n");
goto out4;
- if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
+ }
+ if (IS_MNT_SHARED(root_mnt->mnt_parent)) {
+ printk(KERN_ERR "IS_MNT_SHARED(root_mnt->mnt_parent)\n");
goto out4;
- if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
+ }
+ if (!check_mnt(root_mnt) || !check_mnt(new_mnt)) {
+ printk(KERN_ERR "!check_mnt(root_mnt) || !check_mnt(new_mnt)\n");
+ goto out4;
+ }
+ if (new_mnt->mnt.mnt_flags & MNT_LOCKED) {
+ printk(KERN_ERR "new_mnt->mnt.mnt_flags & MNT_LOCKED\n");
goto out4;
+ }
error = -ENOENT;
- if (d_unlinked(new.dentry))
+ if (d_unlinked(new.dentry)) {
+ printk(KERN_ERR "d_unlinked(new.dentry)\n");
goto out4;
+ }
error = -EBUSY;
- if (new_mnt == root_mnt || old_mnt == root_mnt)
+ if (new_mnt == root_mnt || old_mnt == root_mnt) {
+ printk(KERN_ERR "new_mnt == root_mnt || old_mnt == root_mnt\n");
goto out4; /* loop, on the same file system */
+ }
error = -EINVAL;
- if (root.mnt->mnt_root != root.dentry)
+ if (root.mnt->mnt_root != root.dentry) {
+ printk(KERN_ERR "root.mnt->mnt_root != root.dentry\n");
goto out4; /* not a mountpoint */
- if (!mnt_has_parent(root_mnt))
+ }
+ if (!mnt_has_parent(root_mnt)) {
+ printk(KERN_ERR "!mnt_has_parent(root_mnt)\n");
goto out4; /* not attached */
+ }
root_mp = root_mnt->mnt_mp;
- if (new.mnt->mnt_root != new.dentry)
+ if (new.mnt->mnt_root != new.dentry) {
+ printk(KERN_ERR "new.mnt->mnt_root != new.dentry\n");
goto out4; /* not a mountpoint */
- if (!mnt_has_parent(new_mnt))
+ }
+ if (!mnt_has_parent(new_mnt)) {
+ printk(KERN_ERR "!mnt_has_parent(new_mnt)\n");
goto out4; /* not attached */
+ }
/* make sure we can reach put_old from new_root */
- if (!is_path_reachable(old_mnt, old.dentry, &new))
+ if (!is_path_reachable(old_mnt, old.dentry, &new)) {
+ printk(KERN_ERR "!is_path_reachable(old_mnt, old.dentry, &new)\n");
goto out4;
+ }
/* make certain new is below the root */
- if (!is_path_reachable(new_mnt, new.dentry, &root))
+ if (!is_path_reachable(new_mnt, new.dentry, &root)) {
+ printk(KERN_ERR "!is_path_reachable(new_mnt, new.dentry, &root)\n");
goto out4;
+ }
root_mp->m_count++; /* pin it so it won't go away */
lock_mount_hash();
detach_mnt(new_mnt, &parent_path);
--
2.7.4
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