On Mon, May 5, 2014 at 3:00 PM, Andrew Morton <a...@linux-foundation.org> wrote: > On Thu, 1 May 2014 14:26:33 -0700 Kees Cook <keesc...@chromium.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.
Great, thanks! > 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. I was worried we'd miss different processed tripping it later. On the other hand, I didn't like the idea of being able to spam dmesg. Do you want me to send a patch to replace that with pr_warn_once()? -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
