Date: Mon, 6 Feb 2012 08:27:38 +0400 From: Solar Designer <solar@...nwall.com> To: oss-security@...ts.openwall.com Subject: CVE-2011-3637 Linux kernel: proc: fix Oops on invalid /proc/<pid>/maps access Hi, I just analyzed this issue a little bit and thought I'd post a followup to the thread on oss-security, but to my surprise I could not find the issue mentioned in here, even though "nearby" ones (e.g. fixed in RHEL at about the same time) were brought to this list. I guess this has to do with differences in CVE assignment - when an issue already has a CVE ID, it is less likely to be brought up in here - which I find wrong. This shouldn't be just a CVE ID assignment list, but a general Open Source security list. Anyway, to the specific issue: http://rhn.redhat.com/errata/RHSA-2012-0007.html says "A missing validation flaw was found in the Linux kernel's m_stop() implementation. A local, unprivileged user could use this flaw to trigger a denial of service. (CVE-2011-3637, Moderate)" So I wanted to verify whether the impact is in fact limited to a DoS. More links: https://bugzilla.redhat.com/show_bug.cgi?id=747848 The fix, which I confirmed that it's included in at least OpenVZ's linux-2.6.18-274.17.1.el5.028stab097.1, which is what I happen to care about at this time: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=76597cd31470fa130784c78fadb4dab2e624a723 - vma_stop(priv, vma); + if (!IS_ERR(vma)) + vma_stop(priv, vma); Linus' commit message: "When m_start returns an error, the seq_file logic will still call m_stop with that error entry, so we'd better make sure that we check it before using it as a vma. Introduced by commit ec6fd8a4355c ("report errors in /proc/*/*map* sanely"), which replaced NULL with various ERR_PTR() cases. (On ia64, you happen to get a unaligned fault instead of a page fault, since the address used is generally some random error code like -EPERM)" The commit referenced above as one that introduced the bug: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=ec6fd8a4355c Thus, _assuming_ that the bug was in fact introduced by that commit alone, it does appear to me that we have a mere DoS here - the pointer being referenced has to be some -Exxx access code and nothing more arbitrary. Good. (Additionally, the current fix only catches 4095 possible values, so if the problem were worse, it would be insufficient.) Alexander
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