linux-kernel - [PATCH 3.16 120/192] ext3: preserve i_mode if ext2_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 3.16 120/192] ext3: preserve i_mode if ext2_set_acl() fails

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

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

From: Ben Hutchings <ben@...adent.org.uk>

Based on Ernesto A. Fernández's fix for ext2 (commit fe26569eb919), from
which the following description is taken:

> When changing a file's acl mask, ext2_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.

Cc: Ernesto A. Fernández <ernesto.mnd.fernandez@...il.com>
Cc: Jan Kara <jack@...e.cz>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext3/acl.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/fs/ext3/acl.c
+++ b/fs/ext3/acl.c
@@ -227,19 +227,25 @@ ext3_set_acl(struct inode *inode, struct
 {
 	handle_t *handle;
 	int error, retries = 0;
+	int update_mode = 0;
+	umode_t mode = inode->i_mode;
 
 retry:
 	handle = ext3_journal_start(inode, EXT3_DATA_TRANS_BLOCKS(inode->i_sb));
 	if (IS_ERR(handle))
 		return PTR_ERR(handle);
 	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 journal_stop;
+		update_mode = 1;
+	}
+	error = __ext3_set_acl(handle, inode, type, acl);
+	if (!error && update_mode) {
+		inode->i_mode = mode;
 		inode->i_ctime = CURRENT_TIME_SEC;
 		ext3_mark_inode_dirty(handle, inode);
 	}
-	error = __ext3_set_acl(handle, inode, type, acl);
 journal_stop:
 	ext3_journal_stop(handle);
 	if (error == -ENOSPC && ext3_should_retry_alloc(inode->i_sb, &retries))