x86/ras/mce_amd_inj: Return early on invalid input

Invalid inputs such as these are currently reported in dmesg as
failing:

  $> echo sweet > flags
  [  122.079139] flags_write: Invalid flags value: et

even though the 'flags' attribute has been updated correctly:

  $> cat flags
  sw

This is because userspace keeps writing the remaining buffer
until it encounters an error.

However, the input as a whole is wrong and we should not be
writing anything to the file. Therefore, correct flags_write()
to return -EINVAL immediately on bad input strings.

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/1443190851-2172-2-git-send-email-Aravind.Gopalakrishnan@amd.com
Link: http://lkml.kernel.org/r/1444641762-9437-3-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/arch/x86/ras/mce_amd_inj.c b/arch/x86/ras/mce_amd_inj.c
index 17e35b5bf779..4fd8bb9b90b9 100644
--- a/arch/x86/ras/mce_amd_inj.c
+++ b/arch/x86/ras/mce_amd_inj.c
@@ -129,12 +129,9 @@ static ssize_t flags_write(struct file *filp, const char __user *ubuf,
 {
         char buf[MAX_FLAG_OPT_SIZE], *__buf;
         int err;
-        size_t ret;
 
         if (cnt > MAX_FLAG_OPT_SIZE)
-                cnt = MAX_FLAG_OPT_SIZE;
-
-        ret = cnt;
+                return -EINVAL;
 
         if (copy_from_user(&buf, ubuf, cnt))
                 return -EFAULT;
@@ -150,9 +147,9 @@ static ssize_t flags_write(struct file *filp, const char __user *ubuf,
                 return err;
         }
 
-        *ppos += ret;
+        *ppos += cnt;
 
-        return ret;
+        return cnt;
 }
 
 static const struct file_operations flags_fops = {