[49/63] fix deadlock in pivot_root()
From: Greg KH
Date: Fri Mar 25 2011 - 20:05:00 EST
2.6.38-stable review patch. If anyone has any objections, please let us know.
------------------
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
commit 27cb1572e3e6bb1f8cf6bb3d74c914a87b131792 upstream.
Don't hold vfsmount_lock over the loop traversing ->mnt_parent;
do check_mnt(new.mnt) under namespace_sem instead; combined with
namespace_sem held over all that code it'll guarantee the stability
of ->mnt_parent chain all the way to the root.
Doing check_mnt() outside of namespace_sem in case of pivot_root()
is wrong anyway.
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
fs/namespace.c | 16 +++++-----------
1 file changed, 5 insertions(+), 11 deletions(-)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2469,9 +2469,6 @@ SYSCALL_DEFINE2(pivot_root, const char _
error = user_path_dir(new_root, &new);
if (error)
goto out0;
- error = -EINVAL;
- if (!check_mnt(new.mnt))
- goto out1;
error = user_path_dir(put_old, &old);
if (error)
@@ -2491,7 +2488,7 @@ SYSCALL_DEFINE2(pivot_root, const char _
IS_MNT_SHARED(new.mnt->mnt_parent) ||
IS_MNT_SHARED(root.mnt->mnt_parent))
goto out2;
- if (!check_mnt(root.mnt))
+ if (!check_mnt(root.mnt) || !check_mnt(new.mnt))
goto out2;
error = -ENOENT;
if (cant_mount(old.dentry))
@@ -2515,19 +2512,19 @@ SYSCALL_DEFINE2(pivot_root, const char _
goto out2; /* not attached */
/* make sure we can reach put_old from new_root */
tmp = old.mnt;
- br_write_lock(vfsmount_lock);
if (tmp != new.mnt) {
for (;;) {
if (tmp->mnt_parent == tmp)
- goto out3; /* already mounted on put_old */
+ goto out2; /* already mounted on put_old */
if (tmp->mnt_parent == new.mnt)
break;
tmp = tmp->mnt_parent;
}
if (!is_subdir(tmp->mnt_mountpoint, new.dentry))
- goto out3;
+ goto out2;
} else if (!is_subdir(old.dentry, new.dentry))
- goto out3;
+ goto out2;
+ br_write_lock(vfsmount_lock);
detach_mnt(new.mnt, &parent_path);
detach_mnt(root.mnt, &root_parent);
/* mount old root on put_old */
@@ -2550,9 +2547,6 @@ out1:
path_put(&new);
out0:
return error;
-out3:
- br_write_unlock(vfsmount_lock);
- goto out2;
}
static void __init init_mount_tree(void)
--
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