linux-kernel - [PATCH 02/12] vfs: move permission checking into notify

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Date:   Fri, 16 Sep 2016 14:19:21 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        <stable@...r.kernel.org>
Subject: [PATCH 02/12] 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: Aihua Zhang <zhangaihua1@...wei.com>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Tested-by: Aihua Zhang <zhangaihua1@...wei.com>
Cc: <stable@...r.kernel.org> # v3.18+
---
 fs/attr.c          | 15 +++++++++++++++
 fs/utimes.c        | 17 +----------------
 include/linux/fs.h |  1 +
 3 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index 42bb42bb3c72..3c42cab06b5d 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -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 */
diff --git a/fs/utimes.c b/fs/utimes.c
index 794f5f5b1fb5..ba54b9e648c9 100644
--- a/fs/utimes.c
+++ b/fs/utimes.c
@@ -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 @@ retry_deleg:
 			goto retry_deleg;
 	}
 
-mnt_drop_write_and_out:
 	mnt_drop_write(path->mnt);
 out:
 	return error;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 901e25d495cc..7c391366fb43 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -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
-- 
2.5.5