linux-kernel - [patch 007/164] cpumask: fix compat getaffinity

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Date:	Thu, 01 Jul 2010 10:33:13 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Arnd Bergmann <arnd@...db.de>, Andi Kleen <andi@...stfloor.org>
Subject: [patch 007/164] cpumask: fix compat getaffinity

2.6.33-stable review patch.  If anyone has any objections, please let me know.

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

From: KOSAKI Motohiro <kosaki.motohiro@...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@...fujitsu.com>
Acked-by: Rusty Russell <rusty@...tcorp.com.au>
Acked-by: Arnd Bergmann <arnd@...db.de>
Reported-by: Ken Werner <ken.werner@....de>
Cc: Andi Kleen <andi@...stfloor.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

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

--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -494,29 +494,26 @@ 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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