On Wed, Apr 1, 2015 at 10:31 AM, Heinrich Schuchardt <[email protected]> wrote: > On 01.04.2015 00:45, Andrew Morton wrote: >> On Sun, 29 Mar 2015 21:28:29 +0200 Heinrich Schuchardt <[email protected]> >> wrote: >> >>> When converting unsigned long to int overflows may occur. >>> These currently are not detected when writing to the sysctl >>> file system. >>> >>> E.g. on a system where int has 32 bits and long has 64 bits >>> echo 0x800001234 > /proc/sys/kernel/threads-max >>> has the same effect as >>> echo 0x1234 > /proc/sys/kernel/threads-max >>> >>> The patch adds the missing check in do_proc_dointvec_conv. >>> >>> With the patch an overflow will result in an error EINVAL when >>> writing to the the sysctl file system. >> >> hm, why fix this? There's a small risk of breaking >> accidentally-working userspace, but I expect we can live with that. >> >> But how big a problem is this, really? This behaviour is quite >> expected, after all. >> > > The typical user of a Linux system has never read the Kernel code and > possibly has limited programming experience. > Furthermore in Documentation/sysctl/kernel.txt there is no hint that > only 32-bit integers can be used. > So why should this typical user expect that on a 64-bit system > +3000000000 is considered a negative number? > > Now that we know this is a bug why shouldn't we fix it?
I think this is worth fixing. It is, from a certain perspective, "unexpected behavior". At the very least we could tie it to the sysctl_writes_strict flag? Anything depending on an overflow to get "correct" results seems extremely unlikely to me. -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
