Subject: [PATCH] powerpc/pseries: Correct string length in pseries_of_derive_parent()

From: Nathan Fontenot <[email-masked]>
Date: Mon, 26 Oct 2015 14:33:05 -0500

Commit a030e1e4bbd085bbcfd0a23f8d355fcd41f39bed made a change to use
kstrndup() instead of kmalloc() + strlcpy() in pseries_of_derive_parent()
which introduces a subtle change in the parent path name generated.
The kstrndup() routine will copy n characters followed by a terminating null,
whereas strlcpy() will copy n-1 characters and add a terminating null.

This slight difference results in having a parent path that includes the
trailing '/' character, i.e. "/cpus/" vs. "/cpus". This then causes the
subsequent call to of_find_node_by_path() to fail, and in the case of
DLPAR add operations, the DLPAR request fails.

This patch reduces the total length of the string to copy in kstrndup by 1
so we no longer copy the trailing '/'.

Signed-off-by: Nathan Fontenot <[email-masked]>
---
 arch/powerpc/platforms/pseries/of_helpers.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/of_helpers.c b/arch/powerpc/platforms/pseries/of_helpers.c
index 4417afe..6d90378 100644
--- a/arch/powerpc/platforms/pseries/of_helpers.c
+++ b/arch/powerpc/platforms/pseries/of_helpers.c
@@ -24,7 +24,7 @@ struct device_node *pseries_of_derive_parent(const char *path)
 		return ERR_PTR(-EINVAL);
 
 	if (tail > path + 1) {
-		parent_path = kstrndup(path, tail - path, GFP_KERNEL);
+		parent_path = kstrndup(path, (tail - 1) - path, GFP_KERNEL);
 		if (!parent_path)
 			return ERR_PTR(-ENOMEM);
 	}