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
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