tmpfs: clear S_ISGID when setting posix ACLs

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@huawei.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Brad Spengler <spender@grsecurity.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 5 deletions

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 595522022aca..c9d48dc78495 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -922,11 +922,10 @@ int simple_set_acl(struct inode *inode, struct posix_acl *acl, int type)
         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(inode);