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Date: Mon, 29 Sep 2014 22:04:58 +0200 From: Hannes Frederic Sowa <hannes@...hat.com> To: Kees Cook <keescook@...omium.org> Cc: David Laight <David.Laight@...lab.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, Jason Wang <jasowang@...hat.com>, Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>, "Michael S. Tsirkin" <mst@...hat.com>, Tom Herbert <therbert@...gle.com>, Masatake YAMATO <yamato@...hat.com>, Xi Wang <xii@...gle.com>, stephen hemminger <stephen@...workplumber.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: Re: [PATCH] tun: make sure interface usage can not overflow On Mo, 2014-09-29 at 12:41 -0700, Kees Cook wrote: > On Mon, Sep 29, 2014 at 4:04 AM, David Laight <David.Laight@...lab.com> wrote: > > From: Kees Cook > >> This makes the size argument a const, since it is always populated by > >> the caller. > > > > There is almost no point making parameters 'const. > > ('const foo *' makes sense). > > > >> Additionally double-checks to make sure the copy_from_user > >> can never overflow, keeping CONFIG_DEBUG_STRICT_USER_COPY_CHECKS happy: > >> > >> In function 'copy_from_user', > >> inlined from '__tun_chr_ioctl' at drivers/net/tun.c:1871:7: > >> ... copy_from_user() buffer size is not provably correct > > > > If 'ifreq_len' could be too big then you want to error the ioctl, not panic. > > If it can't be too big you don't need the check. > > The ifreq_len comes from the callers, and is the output of "sizeof" > which is const. Changing the function parameter to "const" means any > changes made in the future where the incoming value isn't const, the > compiler will throw a warning. Hmmm, I think you want something like BUILD_BUG_ON(! __builtin_constant_p(var)). const in function argument only ensures that the value cannot be modified in the function. Bye, Hannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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