linux-kernel - [PATCH 3.16 129/192] f2fs: preserve i_mode if __f2fs_set

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Message-ID: <lsq.1507553064.859981333@decadent.org.uk>
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, "Chao Yu" <yuchao0@...wei.com>,
        "Ernesto A. Fernández" 
        <ernesto.mnd.fernandez@...il.com>,
        "Jaegeuk Kim" <jaegeuk@...nel.org>
Subject: [PATCH 3.16 129/192] f2fs: preserve i_mode if __f2fs_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 14af20fcb1833dd776822361891963c90f7b0262 upstream.

When changing a file's acl mask, __f2fs_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>
Reviewed-by: Chao Yu <yuchao0@...wei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/f2fs/acl.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/f2fs/acl.c
+++ b/fs/f2fs/acl.c
@@ -202,6 +202,7 @@ static int __f2fs_set_acl(struct inode *
 	void *value = NULL;
 	size_t size = 0;
 	int error;
+	umode_t mode = inode->i_mode;

 	if (acl) {
 		error = posix_acl_valid(acl);
@@ -213,10 +214,10 @@ static int __f2fs_set_acl(struct inode *
 	case ACL_TYPE_ACCESS:
 		name_index = F2FS_XATTR_INDEX_POSIX_ACL_ACCESS;
 		if (acl && !ipage) {
-			error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			error = posix_acl_update_mode(inode, &mode, &acl);
 			if (error)
 				return error;
-			set_acl_inode(fi, inode->i_mode);
+			set_acl_inode(fi, mode);
 		}
 		break;