On Mo, 2014-09-29 at 12:41 -0700, Kees Cook wrote: > On Mon, Sep 29, 2014 at 4:04 AM, David Laight <[email protected]> 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 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/
