linux-kernel - [PATCH 3.16 123/192] reiserfs: preserve i_mode if __reiserfs_set

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Date:   Mon, 09 Oct 2017 13:44:24 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jan Kara" <jack@...e.cz>,
        "Ernesto A. Fernández" 
        <ernesto.mnd.fernandez@...il.com>
Subject: [PATCH 3.16 123/192] reiserfs: preserve i_mode if __reiserfs_set_acl()
 fails

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ernesto A. Fernández
 <ernesto.mnd.fernandez@...il.com>

commit fcea8aed91f53b51f9b943dc01f12d8aa666c720 upstream.

When changing a file's acl mask, reiserfs_set_acl() will first set the
group bits of i_mode to the value of the mask, and only then set the
actual extended attribute representing the new acl.

If the second part fails (due to lack of space, for example) and the
file had no acl attribute to begin with, the system will from now on
assume that the mask permission bits are actual group permission bits,
potentially granting access to the wrong users.

Prevent this by only changing the inode mode after the acl has been set.

Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@...il.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/reiserfs/xattr_acl.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/fs/reiserfs/xattr_acl.c
+++ b/fs/reiserfs/xattr_acl.c
@@ -23,7 +23,8 @@ reiserfs_set_acl(struct inode *inode, st
 	struct reiserfs_transaction_handle th;
 	size_t jcreate_blocks;
 	int size = acl ? posix_acl_xattr_size(acl->a_count) : 0;
-
+	int update_mode = 0;
+	umode_t mode = inode->i_mode;
 
 	/*
 	 * Pessimism: We can't assume that anything from the xattr root up
@@ -38,12 +39,14 @@ reiserfs_set_acl(struct inode *inode, st
 	reiserfs_write_unlock(inode->i_sb);
 	if (error == 0) {
 		if (type == ACL_TYPE_ACCESS && acl) {
-			error = posix_acl_update_mode(inode, &inode->i_mode,
-						      &acl);
+			error = posix_acl_update_mode(inode, &mode, &acl);
 			if (error)
 				goto unlock;
+			update_mode = 1;
 		}
 		error = __reiserfs_set_acl(&th, inode, type, acl);
+		if (!error && update_mode)
+			inode->i_mode = mode;
 unlock:
 		reiserfs_write_lock(inode->i_sb);
 		error2 = journal_end(&th);