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From: Greg KH on 1 Jul 2010 18:10
2.6.34-stable review patch. If anyone has any objections, please let me know.

------------------

From: KOSAKI Motohiro <kosaki.motohiro(a)jp.fujitsu.com>

commit fa9dc265ace9774e62f0e31108e5f47911124bda upstream.

Commit a45185d2d "cpumask: convert kernel/compat.c" broke libnuma, which
abuses sched_getaffinity to find out NR_CPUS in order to parse
/sys/devices/system/node/node*/cpumap.

On NUMA systems with less than 32 possibly CPUs, the current
compat_sys_sched_getaffinity now returns '4' instead of the actual
NR_CPUS/8, which makes libnuma bail out when parsing the cpumap.

The libnuma call sched_getaffinity(0, bitmap, 4096) at first. It mean
the libnuma expect the return value of sched_getaffinity() is either len
argument or NR_CPUS. But it doesn't expect to return nr_cpu_ids.

Strictly speaking, userland requirement are

1) Glibc assume the return value mean the lengh of initialized
of mask argument. E.g. if sched_getaffinity(1024) return 128,
glibc make zero fill rest 896 byte.
2) Libnuma assume the return value can be used to guess NR_CPUS
in kernel. It assume len-arg<NR_CPUS makes -EINVAL. But
it try len=4096 at first and 4096 is always bigger than
NR_CPUS. Then, if we remove strange min_length normalization,
we never hit -EINVAL case.

sched_getaffinity() already solved this issue. This patch adapts
compat_sys_sched_getaffinity() to match the non-compat case.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro(a)jp.fujitsu.com>
Acked-by: Rusty Russell <rusty(a)rustcorp.com.au>
Acked-by: Arnd Bergmann <arnd(a)arndb.de>
Reported-by: Ken Werner <ken.werner(a)web.de>
Cc: Andi Kleen <andi(a)firstfloor.org>
Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
kernel/compat.c | 25 +++++++++++--------------
1 file changed, 11 insertions(+), 14 deletions(-)

--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -495,29 +495,26 @@ asmlinkage long compat_sys_sched_getaffi
{
int ret;
cpumask_var_t mask;
- unsigned long *k;
- unsigned int min_length = cpumask_size();

- if (nr_cpu_ids <= BITS_PER_COMPAT_LONG)
- min_length = sizeof(compat_ulong_t);
-
- if (len < min_length)
+ if ((len * BITS_PER_BYTE) < nr_cpu_ids)
+ return -EINVAL;
+ if (len & (sizeof(compat_ulong_t)-1))
return -EINVAL;

if (!alloc_cpumask_var(&mask, GFP_KERNEL))
return -ENOMEM;

ret = sched_getaffinity(pid, mask);
- if (ret < 0)
- goto out;
+ if (ret == 0) {
+ size_t retlen = min_t(size_t, len, cpumask_size());

- k = cpumask_bits(mask);
- ret = compat_put_bitmap(user_mask_ptr, k, min_length * 8);
- if (ret == 0)
- ret = min_length;
-
-out:
+ if (compat_put_bitmap(user_mask_ptr, cpumask_bits(mask), retlen * 8))
+ ret = -EFAULT;
+ else
+ ret = retlen;
+ }
free_cpumask_var(mask);
+
return ret;
}



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