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authorAl Viro <viro@zeniv.linux.org.uk>2011-03-18 08:29:36 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2011-03-18 08:54:59 -0400
commit27cb1572e3e6bb1f8cf6bb3d74c914a87b131792 (patch)
tree01e6510de480d3595ccff315d777770490e51f9c
parent9d412a43c3b26e1e549319e5eec26f0829f9f74d (diff)
fix deadlock in pivot_root()
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@zeniv.linux.org.uk>
-rw-r--r--fs/namespace.c16
1 files changed, 5 insertions, 11 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 453529f72df..46cc26b5aaf 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2569,9 +2569,6 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
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)
@@ -2591,7 +2588,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
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))
@@ -2615,19 +2612,19 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
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 */
@@ -2650,9 +2647,6 @@ out1:
path_put(&new);
out0:
return error;
-out3:
- br_write_unlock(vfsmount_lock);
- goto out2;
}
static void __init init_mount_tree(void)