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: