oprofile: Fix uninitialized memory access when writing to writing to oprofilefs

BugLink: http://bugs.launchpad.net/bugs/913373

commit 913050b91eb94f194392dd797b1ff3779f606ac0 upstream.

If oprofilefs_ulong_from_user() is called with count equals
zero, *val remains unchanged. Depending on the implementation it
might be uninitialized.

Change oprofilefs_ulong_from_user()'s interface to return count
on success. Thus, we are able to return early if count equals
zero which avoids using *val uninitialized. Fixing all users of
oprofilefs_ulong_ from_user().

This follows write syscall implementation when count is zero:
"If count is zero ... [and if] no errors are detected, 0 will be
returned without causing any other effect." (man 2 write)

Reported-By: Mike Waychison <mikew@google.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: oprofile-list <oprofile-list@lists.sourceforge.net>
Link: http://lkml.kernel.org/r/20111219153830.GH16765@erda.amd.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Brad Figg <brad.figg@canonical.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/s390/oprofile/init.c b/arch/s390/oprofile/init.c
index 0e358c2cffe..422110a4385 100644
--- a/arch/s390/oprofile/init.c
+++ b/arch/s390/oprofile/init.c
@@ -90,7 +90,7 @@ static ssize_t hwsampler_write(struct file *file, char const __user *buf,
                 return -EINVAL;
 
         retval = oprofilefs_ulong_from_user(&val, buf, count);
-        if (retval)
+        if (retval <= 0)
                 return retval;
 
         if (oprofile_started)