posix_acl: Clear SGID bit when setting file permissions

When file permissions are modified via chmod(2) and the user is not in
the owning group or capable of CAP_FSETID, the setgid bit is cleared in
inode_change_ok().  Setting a POSIX ACL via setxattr(2) sets the file
permissions as well as the new ACL, but doesn't clear the setgid bit in
a similar way; this allows to bypass the check in chmod(2).  Fix that.

References: CVE-2016-7097
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Signed-off-by: Andreas Gruenbacher <[email protected]>
This commit is contained in:
Jan Kara 2016-09-19 17:39:09 +02:00
commit 073931017b
16 changed files with 89 additions and 102 deletions

View file

@ -276,32 +276,26 @@ static int v9fs_xattr_set_acl(const struct xattr_handler *handler,
switch (handler->flags) {
case ACL_TYPE_ACCESS:
if (acl) {
umode_t mode = inode->i_mode;
retval = posix_acl_equiv_mode(acl, &mode);
if (retval < 0)
struct iattr iattr;
retval = posix_acl_update_mode(inode, &iattr.ia_mode, &acl);
if (retval)
goto err_out;
else {
struct iattr iattr;
if (retval == 0) {
/*
* ACL can be represented
* by the mode bits. So don't
* update ACL.
*/
acl = NULL;
value = NULL;
size = 0;
}
/* Updte the mode bits */
iattr.ia_mode = ((mode & S_IALLUGO) |
(inode->i_mode & ~S_IALLUGO));
iattr.ia_valid = ATTR_MODE;
/* FIXME should we update ctime ?
* What is the following setxattr update the
* mode ?
if (!acl) {
/*
* ACL can be represented
* by the mode bits. So don't
* update ACL.
*/
v9fs_vfs_setattr_dotl(dentry, &iattr);
value = NULL;
size = 0;
}
iattr.ia_valid = ATTR_MODE;
/* FIXME should we update ctime ?
* What is the following setxattr update the
* mode ?
*/
v9fs_vfs_setattr_dotl(dentry, &iattr);
}
break;
case ACL_TYPE_DEFAULT: