Date: Tue, 24 Mar 2015 12:51:00 -0400 (EDT) From: cve-assign@...re.org To: ppandit@...hat.com Cc: cve-assign@...re.org, oss-security@...ts.openwall.com Subject: Re: CVE request Linux kernel: fs: btrfs: non-atomic xattr replace operation -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > Linux kernel built with the Btrfs Filesystem support(CONFIG_BTRFS_FS) is > vulnerable to a race condition which leaves the extended attribute(xattr) > empty for a short time window. This could be leveraged to bypass set ACLs and > potentially escalate user privileges. > > An unprivileged user could use this flaw to potentially escalate privileges on > a system. > > https://git.kernel.org/linus/5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339 We would like to restate the security issue somewhat. The commit mentions two separate concerns: (1) "This leaves a time window where readers (getxattr, listxattrs) won't see any value for the xattr" and (2) "Deleting the old xattr value without verifying first if the new xattr will fit." In both cases, apparently the underlying problem is that the code is attempting to accomplish a transition between a previously acceptable state of an object and a new acceptable state of an object, but does this in a way that an intermediate state becomes visible. Because the intermediate state is, for a security-relevant reason, not known to be acceptable, the transition code has a vulnerability (related, in general, to CWE-371). We feel that (1) and (2) are therefore the same type of vulnerability, even though the attack methodology might rely on a race condition only in case (1). Use CVE-2014-9710 for this vulnerability involving improper management of xattr state. > Returning -EEXIST when the flag XATTR_CREATE is given and the xattr > doesn't exist We don't know whether this third concern is a vulnerability. Presumably it would depend on what callers do after the -EEXIST. - -- CVE assignment team, MITRE CVE Numbering Authority M/S M300 202 Burlington Road, Bedford, MA 01730 USA [ PGP key available through http://cve.mitre.org/cve/request_id.html ] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.14 (SunOS) iQEcBAEBAgAGBQJVEZW6AAoJEKllVAevmvmsk44IAKLgwGa2CnmZn+gN53zdhkSX 3RguwbKRz4QbOri829ByHoqo5wpGfsNKi+KHfz77d895w0SbqEoosStqhgXErQy7 bGCVxjf1PwDRthffptsDtwT+NrP2d8uWVcGM1U9dDlBD40VU4a7fRCzYxoReJaAp eyy1aA96gyxFoGZm1vENuMrgDJmMp6EajV3292Acg6cJ/UoPJ7QxNpPtYI8tua/V zXqMprms2jyba7v37+HW6zQ0zELDCWfzSeYkyCOAgGI5oBc1RsKeOyHfWpS1A3sr f5pqfNfUu75+38+xl0Ic+GKxO1reqCkZe6iFu9OkdGtAHXIMMkxLMHpQfP4J9v8= =op6Y -----END PGP SIGNATURE-----
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