Messages in this thread | | | Date | Mon, 03 Jul 2006 20:09:13 -0400 | From | Shailabh Nagar <> | Subject | Re: [Patch][RFC] Disabling per-tgid stats on task exit in taskstats |
| |
Paul Jackson wrote:
>Shailabh wrote: > > >>I don't know if there are buffer overflow >>issues in passing a string >> >> > >I don't know if this comment applies to "the standard netlink way of >passing it up using NLA_STRING", but the way I deal with buffer length >issues in the cpuset code is to insist that the user code express the >list in no fewer than 100 + 6 * NR_CPUS bytes: > >From kernel/cpuset.c: > > /* Crude upper limit on largest legitimate cpulist user might write. */ > if (nbytes > 100 + 6 * NR_CPUS) > return -E2BIG; > >This lets the user specify the buffer size passed in, but prevents >them from trying a denial of service attack on the kernel by trying >to pass in a huge buffer. > >If the user can't figure out how to write the desired cpulist in >that size, then tough toenails. > > Paul,
Perhaps I should use the the other ascii format for specifying cpumasks since its more amenable to specifying an upper bound for the length of the ascii string and is more compact ?
That format (the one used in lib/bitmap.c:bitmap_parse) is comma separated chunks of hex digits with each chunk specifying 32 bits of the desired cpumask.
So ((NR_CPUS + 32) / 32) * 8 + 1 (8 hex characters for each 32 cpus, and 1 extra character for null terminator) would be an upper bound that would accomodate all the cpus for sure.
Thoughts ?
--Shailabh
--Shailabh - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |