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

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: <stable@vger.kernel.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>

2 files changed, 13 insertions, 5 deletions

diff --git a/drivers/oprofile/oprofile_files.c b/drivers/oprofile/oprofile_files.c
index 89f63456646f..84a208dbed93 100644
--- a/drivers/oprofile/oprofile_files.c
+++ b/drivers/oprofile/oprofile_files.c
@@ -45,7 +45,7 @@ static ssize_t timeout_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;
 
         retval = oprofile_set_timeout(val);
@@ -84,7 +84,7 @@ static ssize_t depth_write(struct file *file, char const __user *buf, size_t cou
                 return -EINVAL;
 
         retval = oprofilefs_ulong_from_user(&val, buf, count);
-        if (retval)
+        if (retval <= 0)
                 return retval;
 
         retval = oprofile_set_ulong(&oprofile_backtrace_depth, val);
@@ -141,9 +141,10 @@ static ssize_t enable_write(struct file *file, char const __user *buf, size_t co
                 return -EINVAL;
 
         retval = oprofilefs_ulong_from_user(&val, buf, count);
-        if (retval)
+        if (retval <= 0)
                 return retval;
 
+        retval = 0;
         if (val)
                 retval = oprofile_start();
         else
diff --git a/drivers/oprofile/oprofilefs.c b/drivers/oprofile/oprofilefs.c
index d0de6cc2d7a5..2f0aa0f700e6 100644
--- a/drivers/oprofile/oprofilefs.c
+++ b/drivers/oprofile/oprofilefs.c
@@ -60,6 +60,13 @@ ssize_t oprofilefs_ulong_to_user(unsigned long val, char __user *buf, size_t cou
 }
 
 
+/*
+ * Note: If oprofilefs_ulong_from_user() returns 0, then *val remains
+ * unchanged and might be uninitialized. 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)
+ */
 int oprofilefs_ulong_from_user(unsigned long *val, char const __user *buf, size_t count)
 {
         char tmpbuf[TMPBUFSIZE];
@@ -79,7 +86,7 @@ int oprofilefs_ulong_from_user(unsigned long *val, char const __user *buf, size_
         raw_spin_lock_irqsave(&oprofilefs_lock, flags);
         *val = simple_strtoul(tmpbuf, NULL, 0);
         raw_spin_unlock_irqrestore(&oprofilefs_lock, flags);
-        return 0;
+        return count;
 }
 
 
@@ -99,7 +106,7 @@ static ssize_t ulong_write_file(struct file *file, char const __user *buf, size_
                 return -EINVAL;
 
         retval = oprofilefs_ulong_from_user(&value, buf, count);
-        if (retval)
+        if (retval <= 0)
                 return retval;
 
         retval = oprofile_set_ulong(file->private_data, value);