On 10/27/2015 03:17 AM, Andy Shevchenko wrote:

On Mon, 2015-10-26 at 14:33 -0500, Nathan Fontenot wrote:

quoted

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.

Nice catch!
One comment below.

quoted

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 <redacted>
---
 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);

Since  previous line has (tail > path + 1) which is equivalent to (tail
- 1 > path), can we amend both?

For example (might be better, but first comes to my mind)

const char *tail = kbasename(path) - 1;

Agreed. I'll send out a v2 of the patch with this update and add a comment
to indicate we do not want to include the trailing '\' character.

-Nathan

...

if (tail > path) {

quoted

 		if (!parent_path)
 			return ERR_PTR(-ENOMEM);
 	}