[tip:ras/core] RAS/CEC: Fix pfn insertion

[tip:ras/core] RAS/CEC: Fix pfn insertion

[tip-bot for Borislav Petkov]

Commit-ID:  6d8e294bf5f0e85c34e8b14b064e2965f53f38b0
Gitweb:     https://git.kernel.org/tip/6d8e294bf5f0e85c34e8b14b064e2965f53f38b0
Author:     Borislav Petkov <bp@suse.de>
AuthorDate: Sat, 20 Apr 2019 12:53:05 +0200
Committer:  Borislav Petkov <bp@suse.de>
CommitDate: Sat, 8 Jun 2019 17:32:00 +0200

RAS/CEC: Fix pfn insertion

When inserting random PFNs for debugging the CEC through
(debugfs)/ras/cec/pfn, depending on the return value of pfn_set(),
multiple values get inserted per a single write.

That is because simple_attr_write() interprets a retval of 0 as
success and claims the whole input. However, pfn_set() returns the
cec_add_elem() value, which, if > 0 and smaller than the whole input
length, makes glibc continue issuing the write syscall until there's
input left:

  pfn_set
  simple_attr_write
  debugfs_attr_write
  full_proxy_write
  vfs_write
  ksys_write
  do_syscall_64
  entry_SYSCALL_64_after_hwframe

leading to those repeated calls.

Return 0 to fix that.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
---
 drivers/ras/cec.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c
index 673f8a128397..f5795adc5a6e 100644
--- a/drivers/ras/cec.c
+++ b/drivers/ras/cec.c
@@ -369,7 +369,9 @@ static int pfn_set(void *data, u64 val)
 {
 	*(u64 *)data = val;
 
-	return cec_add_elem(val);
+	cec_add_elem(val);
+
+	return 0;
 }
 
 DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");