linux-kernel - [PATCH 3.2 55/74] ext4: Don't clear SGID when inheriting ACLs

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Message-ID: <lsq.1507552234.938127747@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:30:34 +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>,
        "Andreas Gruenbacher" <agruenba@...hat.com>,
        "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 3.2 55/74] ext4: Don't clear SGID when inheriting ACLs

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

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

From: Jan Kara <jack@...e.cz>

commit a3bb2d5587521eea6dab2d05326abb0afb460abd upstream.

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 moving posix_acl_update_mode() out of
__ext4_set_acl() into ext4_set_acl(). That way the function will not be
called when inheriting ACLs which is what we want as it prevents SGID
bit clearing and the mode has been properly set by posix_acl_create()
anyway.

Fixes: 073931017b49d9458aa351605b43a7e34598caef
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Jan Kara <jack@...e.cz>
Reviewed-by: Andreas Gruenbacher <agruenba@...hat.com>
[bwh: Backported to 3.2: the __ext4_set_acl() function didn't exist,
 so added it]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/acl.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

--- a/fs/ext4/acl.c
+++ b/fs/ext4/acl.c
@@ -183,15 +183,13 @@ ext4_get_acl(struct inode *inode, int ty
  * inode->i_mutex: down unless called from ext4_new_inode
  */
 static int
-ext4_set_acl(handle_t *handle, struct inode *inode, int type,
-	     struct posix_acl *acl)
+__ext4_set_acl(handle_t *handle, struct inode *inode, int type,
+	       struct posix_acl *acl)
 {
 	int name_index;
 	void *value = NULL;
 	size_t size = 0;
 	int error;
-	int update_mode = 0;
-	umode_t mode = inode->i_mode;
 
 	if (S_ISLNK(inode->i_mode))
 		return -EOPNOTSUPP;
@@ -199,12 +197,6 @@ ext4_set_acl(handle_t *handle, struct in
 	switch (type) {
 	case ACL_TYPE_ACCESS:
 		name_index = EXT4_XATTR_INDEX_POSIX_ACL_ACCESS;
-		if (acl) {
-			error = posix_acl_update_mode(inode, &mode, &acl);
-			if (error)
-				return error;
-			update_mode = 1;
-		}
 		break;
 
 	case ACL_TYPE_DEFAULT:
@@ -228,11 +220,31 @@ ext4_set_acl(handle_t *handle, struct in
 	kfree(value);
 	if (!error) {
 		set_cached_acl(inode, type, acl);
-		if (update_mode) {
-			inode->i_mode = mode;
-			inode->i_ctime = ext4_current_time(inode);
-			ext4_mark_inode_dirty(handle, inode);
-		}
+	}
+
+	return error;
+}
+
+static int
+ext4_set_acl(handle_t *handle, struct inode *inode, int type,
+	     struct posix_acl *acl)
+{
+	umode_t mode = inode->i_mode;
+	int update_mode = 0;
+	int error;
+
+	if ((type == ACL_TYPE_ACCESS) && acl) {
+		error = posix_acl_update_mode(inode, &mode, &acl);
+		if (error)
+			return error;
+		update_mode = 1;
+	}
+
+	error = __ext4_set_acl(handle, inode, type, acl);
+	if (!error && update_mode) {
+		inode->i_mode = mode;
+		inode->i_ctime = ext4_current_time(inode);
+		ext4_mark_inode_dirty(handle, inode);
 	}
 
 	return error;
@@ -261,8 +273,8 @@ ext4_init_acl(handle_t *handle, struct i
 	}
 	if (test_opt(inode->i_sb, POSIX_ACL) && acl) {
 		if (S_ISDIR(inode->i_mode)) {
-			error = ext4_set_acl(handle, inode,
-					     ACL_TYPE_DEFAULT, acl);
+			error = __ext4_set_acl(handle, inode,
+					       ACL_TYPE_DEFAULT, acl);
 			if (error)
 				goto cleanup;
 		}
@@ -272,7 +284,7 @@ ext4_init_acl(handle_t *handle, struct i
 
 		if (error > 0) {
 			/* This is an extended ACL */
-			error = ext4_set_acl(handle, inode, ACL_TYPE_ACCESS, acl);
+			error = __ext4_set_acl(handle, inode, ACL_TYPE_ACCESS, acl);
 		}
 	}
 cleanup: