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Commit f2b20f6e authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

vfs: move permission checking into notify_change() for utimes(NULL) 



This fixes a bug where the permission was not properly checked in
overlayfs.  The testcase is ltp/utimensat01.

It is also cleaner and safer to do the permission checking in the vfs
helper instead of the caller.

This patch introduces an additional ia_valid flag ATTR_TOUCH (since
touch(1) is the most obvious user of utimes(NULL)) that is passed into
notify_change whenever the conditions for this special permission checking
mode are met.

Reported-by: default avatarAihua Zhang <zhangaihua1@huawei.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Tested-by: default avatarAihua Zhang <zhangaihua1@huawei.com>
Cc: <stable@vger.kernel.org> # v3.18+
parent e71b9dff

fs/attr.c

+15 −0
Original line number Diff line number Diff line
@@ -202,6 +202,21 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de 
			return -EPERM;

	}



	/*

	 * If utimes(2) and friends are called with times == NULL (or both

	 * times are UTIME_NOW), then we need to check for write permission

	 */

	if (ia_valid & ATTR_TOUCH) {

		if (IS_IMMUTABLE(inode))

			return -EPERM;



		if (!inode_owner_or_capable(inode)) {

			error = inode_permission(inode, MAY_WRITE);

			if (error)

				return error;

		}

	}



	if ((ia_valid & ATTR_MODE)) {

		umode_t amode = attr->ia_mode;

		/* Flag setting protected by i_mutex */

fs/utimes.c

+1 −16
Original line number Diff line number Diff line
@@ -87,21 +87,7 @@ static int utimes_common(struct path *path, struct timespec *times) 
		 */

		newattrs.ia_valid |= ATTR_TIMES_SET;

	} else {

		/*

		 * If times is NULL (or both times are UTIME_NOW),

		 * then we need to check permissions, because

		 * inode_change_ok() won't do it.

		 */

		error = -EPERM;

                if (IS_IMMUTABLE(inode))

			goto mnt_drop_write_and_out;



		error = -EACCES;

		if (!inode_owner_or_capable(inode)) {

			error = inode_permission(inode, MAY_WRITE);

			if (error)

				goto mnt_drop_write_and_out;

		}

		newattrs.ia_valid |= ATTR_TOUCH;

	}

retry_deleg:

	inode_lock(inode);
@@ -113,7 +99,6 @@ static int utimes_common(struct path *path, struct timespec *times) 
			goto retry_deleg;

	}



mnt_drop_write_and_out:

	mnt_drop_write(path->mnt);

out:

	return error;

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -224,6 +224,7 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, 
#define ATTR_KILL_PRIV	(1 << 14)

#define ATTR_OPEN	(1 << 15) /* Truncating from open(O_TRUNC) */

#define ATTR_TIMES_SET	(1 << 16)

#define ATTR_TOUCH	(1 << 17)



/*

 * Whiteout is represented by a char device.  The following constants define the