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 overriden. And here we
only care about APPEND_FL and IMMUTABLE_FL, so get these information from
inode.
Changes since v1:
- remove S_DIRSYNC since ovl_copyflags() does not copy FS_DIRSYNC_FL,
pointed out by Amir Goldstein.
Signed-off-by: Jiufei Xue <jiufei.xue@xxxxxxxxxxxxxxxxx>
---
fs/overlayfs/file.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 84dd957efa24..b5aee3c12579 100644
--- 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 +373,28 @@ static long ovl_real_ioctl(struct file *file, unsigned int cmd,
return ret;
}
+static unsigned int ovl_get_inode_flags(struct inode *inode)
+{
+ unsigned int flags = 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(struct file *file, unsigned int cmd, unsigned long arg)
{
long ret;
struct inode *inode = file_inode(file);
+ unsigned int flags;
switch (cmd) {
case FS_IOC_GETFLAGS:
@@ -386,6 +405,15 @@ static long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
if (!inode_owner_or_capable(inode))
return -EACCES;
+ if (get_user(flags, (int __user *) arg))
+ return -EFAULT;
+
+ /* Check the capability before cred overridden */
+ if ((flags ^ ovl_get_inode_flags(inode)) & (FS_APPEND_FL | FS_IMMUTABLE_FL)) {
+ if (!capable(CAP_LINUX_IMMUTABLE))
+ return -EPERM;
+ }
+
ret = mnt_want_write_file(file);
if (ret)
return ret;
--
2.19.1.856.g8858448bb
