Messages in this thread | | | Date | Wed, 15 Jun 2016 16:50:01 +0800 | From | Dave Young <> | Subject | Re: [PATCH 1/1] kernel/sysctl.c: avoid overflow |
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On 06/15/16 at 10:40am, Willy Tarreau wrote: > On Wed, Jun 15, 2016 at 04:33:32PM +0800, Dave Young wrote: > > On 06/14/16 at 10:41pm, Willy Tarreau wrote: > > > On Tue, Jun 14, 2016 at 01:19:06PM -0700, Andrew Morton wrote: > > > > On Sat, 11 Jun 2016 03:33:08 +0200 Heinrich Schuchardt <xypron.glpk@gmx.de> wrote: > > > > > > > > > An undetected overflow may occur in do_proc_dointvec_minmax_conv_param. > > > > > > > > > > ... > > > > > > > > > > --- a/kernel/sysctl.c > > > > > +++ b/kernel/sysctl.c > > > > > @@ -2313,7 +2313,17 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp, > > > > > { > > > > > struct do_proc_dointvec_minmax_conv_param *param = data; > > > > > if (write) { > > > > > - int val = *negp ? -*lvalp : *lvalp; > > > > > + int val; > > > > > + > > > > > + if (*negp) { > > > > > + if (*lvalp > (unsigned long) INT_MAX + 1) > > > > > + return -EINVAL; > > > > > + val = -*lvalp; > > > > > + } else { > > > > > + if (*lvalp > (unsigned long) INT_MAX) > > > > > + return -EINVAL; > > > > > + val = *lvalp; > > > > > + } > > > > > if ((param->min && *param->min > val) || > > > > > (param->max && *param->max < val)) > > > > > return -EINVAL; > > > > > > > > hm. > > > > > > > > What happens if someone does > > > > > > > > echo -1 > /proc/foo > > > > > > > > expecting to get 0xffffffff? That's a reasonable shorthand, and if we > > > > change that to spit out EINVAL then people's stuff may break. > > > > > > I'd go even further, I don't see anymore how it becomes possible > > > to actually *write* 0xffffffff at all! This function is used by > > > proc_dointvec_minmax() which is used with extra1=&zero and extra2 > > > not set with some unsigned ints to allow the full range to be > > > configured (eg: dirty_expire_interval is the first I found by a > > > quick random look). > > > > sysctl_writes_strict use extra1 = -1 and extra2 = 1 > > > > But I do not get why -1 does not work, 1 < (unsigned long) INT_MAX + 1 > > so val = -1, it is still right? > > -1 should indeed work but 0xffffffff will definitely not.
Hmm, right, indeed.
Below echo works originally: echo 0xffffffff > /proc/sys/kernel/sysctl_writes_strict
> > Willy
Thanks Dave
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