[added to the 4.1 stable tree] ext2: Don't clear SGID when inheriting ACLs

[Sasha Levin <Alexander.Levin@xxxxxxxxxxxxx>]

From: Jan Kara <jack@xxxxxxx>

This patch has been added to the 4.1 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit a992f2d38e4ce17b8c7d1f7f67b2de0eebdea069 ]

When new directory 'DIR1' is created in a directory 'DIR0' with SGID bit
set, DIR1 is expected to have SGID bit set (and owning group equal to
the owning group of 'DIR0'). However when 'DIR0' also has some default
ACLs that 'DIR1' inherits, setting these ACLs will result in SGID bit on
'DIR1' to get cleared if user is not member of the owning group.

Fix the problem by creating __ext2_set_acl() function that does not call
posix_acl_update_mode() and use it when inheriting ACLs. That prevents
SGID bit clearing and the mode has been properly set by
posix_acl_create() anyway.

Fixes: 073931017b49d9458aa351605b43a7e34598caef
CC: stable@xxxxxxxxxxxxxxx
CC: linux-ext4@xxxxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 fs/ext2/acl.c | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/fs/ext2/acl.c b/fs/ext2/acl.c
index d6aeb84e90b6..d882d873c5a3 100644
--- a/fs/ext2/acl.c
+++ b/fs/ext2/acl.c
@@ -178,11 +178,8 @@ ext2_get_acl(struct inode *inode, int type)
 	return acl;
 }
 
-/*
- * inode->i_mutex: down
- */
-int
-ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
+static int
+__ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 {
 	int name_index;
 	void *value = NULL;
@@ -192,13 +189,6 @@ ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 	switch(type) {
 		case ACL_TYPE_ACCESS:
 			name_index = EXT2_XATTR_INDEX_POSIX_ACL_ACCESS;
-			if (acl) {
-				error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
-				if (error)
-					return error;
-				inode->i_ctime = CURRENT_TIME_SEC;
-				mark_inode_dirty(inode);
-			}
 			break;
 
 		case ACL_TYPE_DEFAULT:
@@ -224,6 +214,24 @@ ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 	return error;
 }
 
+/*
+ * inode->i_mutex: down
+ */
+int
+ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
+{
+	int error;
+
+	if (type == ACL_TYPE_ACCESS && acl) {
+		error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+		if (error)
+			return error;
+		inode->i_ctime = CURRENT_TIME_SEC;
+		mark_inode_dirty(inode);
+	}
+	return __ext2_set_acl(inode, acl, type);
+}
+
 /*
  * Initialize the ACLs of a new inode. Called from ext2_new_inode.
  *
@@ -241,12 +249,12 @@ ext2_init_acl(struct inode *inode, struct inode *dir)
 		return error;
 
 	if (default_acl) {
-		error = ext2_set_acl(inode, default_acl, ACL_TYPE_DEFAULT);
+		error = __ext2_set_acl(inode, default_acl, ACL_TYPE_DEFAULT);
 		posix_acl_release(default_acl);
 	}
 	if (acl) {
 		if (!error)
-			error = ext2_set_acl(inode, acl, ACL_TYPE_ACCESS);
+			error = __ext2_set_acl(inode, acl, ACL_TYPE_ACCESS);
 		posix_acl_release(acl);
 	}
 	return error;
-- 
2.14.1