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Date: Mon, 5 May 2014 15:00:16 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Kees Cook <keescook@...omium.org> Cc: linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>, Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Mel Gorman <mgorman@...e.de>, Aaron Tomlin <atomlin@...hat.com>, Li Zefan <lizefan@...wei.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Ryan Mallon <rmallon@...il.com>, Wanpeng Li <liwanp@...ux.vnet.ibm.com>, Dario Faggioli <raistlin@...ux.it>, Jens Axboe <axboe@...com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Frederic Weisbecker <fweisbec@...il.com>, Michael Ellerman <michael@...erman.id.au>, linux-doc@...r.kernel.org Subject: Re: [PATCH v3 0/4] sysctl: fix incorrect write position handling On Thu, 1 May 2014 14:26:33 -0700 Kees Cook <keescook@...omium.org> wrote: > When writing to a sysctl string, each write, regardless of VFS position, > began writing the string from the start. This meant the contents of > the last write to the sysctl controlled the string contents instead of > the first. > > This misbehavior was featured in an exploit against Chrome OS. While it's > not in itself a vulnerability, it's a weirdness that isn't on the mind > of most auditors: "This filter looks correct, the first line written > would not be meaningful to sysctl" doesn't apply here, since the size > of the write and the contents of the final write are what matter when > writing to sysctls. > > This adds the sysctl kernel.sysctl_writes_strict to control the write > behavior. The default (0) reports when VFS position is non-0 on a write, > but retains legacy behavior, -1 disables the warning, and 1 enables the > position-respecting behavior. > OK, let's try that. I added this paragraph to the patchset's overall changelog: : The long-term plan here is to wait for userspace to be fixed in response : to the new warning and to then switch the default kernel behavior to the : new position-respecting behavior. I'm thinking we should use pr_warn_once() in warn_sysctl_write()? Otherwise people will go and shut the thing up permanently and we'll lose the benefits. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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