+From 98487de318a6f33312471ae1e2afa16fbf8361fe Mon Sep 17 00:00:00 2001
+From: Jiufei Xue <jiufei.xue@linux.alibaba.com>
+Date: Mon, 6 May 2019 15:41:02 +0800
+Subject: ovl: check the capability before cred overridden
+
+From: Jiufei Xue <jiufei.xue@linux.alibaba.com>
+
+commit 98487de318a6f33312471ae1e2afa16fbf8361fe upstream.
+
+We found that it return success when we set IMMUTABLE_FL flag to a file in
+docker even though the docker didn't have the capability
+CAP_LINUX_IMMUTABLE.
+
+The commit d1d04ef8572b ("ovl: stack file ops") and dab5ca8fd9dd ("ovl: add
+lsattr/chattr support") implemented chattr operations on a regular overlay
+file. ovl_real_ioctl() overridden the current process's subjective
+credentials with ofs->creator_cred which have the capability
+CAP_LINUX_IMMUTABLE so that it will return success in
+vfs_ioctl()->cap_capable().
+
+Fix this by checking the capability before cred overridden. And here we
+only care about APPEND_FL and IMMUTABLE_FL, so get these information from
+inode.
+
+[SzM: move check and call to underlying fs inside inode locked region to
+prevent two such calls from racing with each other]
+
+Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
+Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
+Cc: Amir Goldstein <amir73il@gmail.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/overlayfs/file.c | 79 ++++++++++++++++++++++++++++++++++++++++------------
+ 1 file changed, 61 insertions(+), 18 deletions(-)
+
+--- a/fs/overlayfs/file.c
++++ b/fs/overlayfs/file.c
+@@ -11,6 +11,7 @@
+ #include <linux/mount.h>
+ #include <linux/xattr.h>
+ #include <linux/uio.h>
++#include <linux/uaccess.h>
+ #include "overlayfs.h"
+
+ static char ovl_whatisit(struct inode *inode, struct inode *realinode)
+@@ -372,10 +373,68 @@ static long ovl_real_ioctl(struct file *
+ return ret;
+ }
+
+-static long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
++static unsigned int ovl_get_inode_flags(struct inode *inode)
++{
++ unsigned int flags = READ_ONCE(inode->i_flags);
++ unsigned int ovl_iflags = 0;
++
++ if (flags & S_SYNC)
++ ovl_iflags |= FS_SYNC_FL;
++ if (flags & S_APPEND)
++ ovl_iflags |= FS_APPEND_FL;
++ if (flags & S_IMMUTABLE)
++ ovl_iflags |= FS_IMMUTABLE_FL;
++ if (flags & S_NOATIME)
++ ovl_iflags |= FS_NOATIME_FL;
++
++ return ovl_iflags;
++}
++
++static long ovl_ioctl_set_flags(struct file *file, unsigned long arg)
+ {
+ long ret;
+ struct inode *inode = file_inode(file);
++ unsigned int flags;
++ unsigned int old_flags;
++
++ if (!inode_owner_or_capable(inode))
++ return -EACCES;
++
++ if (get_user(flags, (int __user *) arg))
++ return -EFAULT;
++
++ ret = mnt_want_write_file(file);
++ if (ret)
++ return ret;
++
++ inode_lock(inode);
++
++ /* Check the capability before cred override */
++ ret = -EPERM;
++ old_flags = ovl_get_inode_flags(inode);
++ if (((flags ^ old_flags) & (FS_APPEND_FL | FS_IMMUTABLE_FL)) &&
++ !capable(CAP_LINUX_IMMUTABLE))
++ goto unlock;
++
++ ret = ovl_maybe_copy_up(file_dentry(file), O_WRONLY);
++ if (ret)
++ goto unlock;
++
++ ret = ovl_real_ioctl(file, FS_IOC_SETFLAGS, arg);
++
++ ovl_copyflags(ovl_inode_real(inode), inode);
++unlock:
++ inode_unlock(inode);
++
++ mnt_drop_write_file(file);
++
++ return ret;
++
++}
++
++static long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
++{
++ long ret;
+
+ switch (cmd) {
+ case FS_IOC_GETFLAGS:
+@@ -383,23 +442,7 @@ static long ovl_ioctl(struct file *file,
+ break;
+
+ case FS_IOC_SETFLAGS:
+- if (!inode_owner_or_capable(inode))
+- return -EACCES;
+-
+- ret = mnt_want_write_file(file);
+- if (ret)
+- return ret;
+-
+- ret = ovl_maybe_copy_up(file_dentry(file), O_WRONLY);
+- if (!ret) {
+- ret = ovl_real_ioctl(file, cmd, arg);
+-
+- inode_lock(inode);
+- ovl_copyflags(ovl_inode_real(inode), inode);
+- inode_unlock(inode);
+- }
+-
+- mnt_drop_write_file(file);
++ ret = ovl_ioctl_set_flags(file, arg);
+ break;
+
+ default: