[PATCH 3/5] mm, util: Do strndup_user allocation directly, instead of through memdup_user

[Ezequiel Garcia <elezegarcia@gmail.com>]

Since the allocation was being done throug memdup_user, the caller
is wrongly traced as being strndup_user (the correct trace should
report the caller of strndup_user).

This is a common problem: in order to get accurate callsite tracing,
a utils function can't allocate through another utils function,
but instead do the allocation himself.

Cc: Pekka Enberg <penberg@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
---
I'm not sure this is the best solution,
but creating another function to reuse between strndup_user
and memdup_user seemed like an overkill.

 mm/util.c |   15 ++++++++++++---
 1 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index dc3036c..87ff667 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -214,10 +214,19 @@ char *strndup_user(const char __user *s, long n)
 	if (length > n)
 		return ERR_PTR(-EINVAL);
 
-	p = memdup_user(s, length);
+	/*
+	 * Always use GFP_KERNEL, since copy_from_user() can sleep and
+	 * cause pagefault, which makes it pointless to use GFP_NOFS
+	 * or GFP_ATOMIC.
+	 */
+	p = kmalloc_track_caller(length, GFP_KERNEL);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
 
-	if (IS_ERR(p))
-		return p;
+	if (copy_from_user(p, s, length)) {
+		kfree(p);
+		return ERR_PTR(-EFAULT);
+	}
 
 	p[length - 1] = '\0';
 
-- 
1.7.8.6

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