[PATCH 3.16 08/12] tmpfs: clear S_ISGID when setting posix ACLs

From: Ben Hutchings
Date: Fri Feb 24 2017 - 07:13:26 EST


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

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

From: Gu Zheng <guzheng1@xxxxxxxxxx>

commit 497de07d89c1410d76a15bec2bb41f24a2a89f31 upstream.

This change was missed the tmpfs modification in In CVE-2016-7097
commit 073931017b49 ("posix_acl: Clear SGID bit when setting
file permissions")
It can test by xfstest generic/375, which failed to clear
setgid bit in the following test case on tmpfs:

touch $testfile
chown 100:100 $testfile
chmod 2755 $testfile
_runas -u 100 -g 101 -- setfacl -m u::rwx,g::rwx,o::rwx $testfile

Signed-off-by: Gu Zheng <guzheng1@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
fs/posix_acl.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -904,11 +904,10 @@ int simple_set_acl(struct inode *inode,
int error;

if (type == ACL_TYPE_ACCESS) {
- error = posix_acl_equiv_mode(acl, &inode->i_mode);
- if (error < 0)
- return 0;
- if (error == 0)
- acl = NULL;
+ error = posix_acl_update_mode(inode,
+ &inode->i_mode, &acl);
+ if (error)
+ return error;
}

inode->i_ctime = CURRENT_TIME;