Date: Fri, 22 Apr 2022 18:02:58 +0200 From: Salvatore Bonaccorso <carnil@...ian.org> To: David Bouman <dbouman03@...il.com> Cc: oss-security@...ts.openwall.com Subject: Re: Linux: UaF due to concurrency issue in io_uring timeouts Hi David, On Fri, Apr 22, 2022 at 02:43:27AM +0200, David Bouman wrote: > Hello list, > > We (Jayden Rivers and David Bouman) are disclosing a bug we found in the > Linux kernel's io_uring subsystem. We have written a local privilege > escalation PoC that can successfully elevate to system root from an > unprivileged process (in a container). We will be releasing a blog post > (including exploit code) in a week or two. It should be noted that unlike > many Linux vulnerabilities that have surfaced recently, triggering this one > does not require an attacker to have any kind of privileges (e.g. in a user > namespace). This leaves many systems vulnerable. > > We are still looking for a CNA representative that can assign a CVE number > for this vulnerability; please contact us! > > Kernel versions 5.10+ are affected, and linux-stable patches are already > pushed. The upstream patch commit is > e677edbcabee849bfdd43f1602bccbecf736a646 ("io_uring: fix race between > timeout flush and removal"). > > When the IORING_OP_TIMEOUT (T) and IORING_OP_LINK_TIMEOUT (LT) opcodes are > combined in a linked submission queue entry, and another request (B) > finishes, a race might occur: namely, when due to the completion of B, T is > cancelled (through the completion event count), and LT is canceled by its > hrtimer at the same time. Whilst T is still being cleaned up, LT is already > freed by a different execution context, and since they are linked, the > cleanup of T retains a dangling reference to the now-freed LT. Hence, > there's a use-after-free. > > Exploitation-wise, the attacker can reallocate LT to another `struct > io_kiocb` and defer the UaF to e.g. a `struct file` (this is the technique > we will describe in aforementioned blog post). > > The race window is quite tight and the scenario is complicated, so the race > can only be won very infrequently in our experience. > > It is advised to upgrade your kernel to latest ASAP. > > Greetings, > > Jayden Rivers & David Bouman This has CVE-2022-29582 assigned. https://www.cve.org/CVERecord?id=CVE-2022-29582 Regards, Salvatore
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