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Date: Tue, 12 Feb 2019 14:55:18 +0100
From: Florian Weimer <fweimer@...hat.com>
To: Aleksa Sarai <cyphar@...har.com>
Cc: oss-security@...ts.openwall.com, dev@...ncontainers.org, Christian Brauner <christian.brauner@...ntu.com>
Subject: Re: CVE-2019-5736: runc container breakout (all versions)
* Aleksa Sarai:
> + memfd = memfd_create(MEMFD_COMMENT, MFD_CLOEXEC|MFD_ALLOW_SEALING);
> + if (memfd < 0)
> + goto err_binfd;
Is it really necessary to use a memfd_create here? Do you really need
sealing? It's a bit odd to add a new system call dependency in a
security update. The ability fexecve a memfd descriptor is also rather
odd. I wouldn't have expected execute permissions on memfd descriptors,
so this sounds like a kernel bug (which now can't be fixed).
I saw some other patch with a O_TMPFILE replacement. Does this really
work? It's possible to create a new name with linkat, so that's not a
real win security-wise. Could you just make a copy, under a different
owner, and not care how it is going to be modified?
Thanks,
Florian
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