linux-kernel - [PATCH AUTOSEL 4.19 049/158] RAS/CEC: Fix pfn insertion

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Date:   Mon, 15 Jul 2019 10:16:20 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Borislav Petkov <bp@...e.de>, Tony Luck <tony.luck@...el.com>,
        linux-edac <linux-edac@...r.kernel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.19 049/158] RAS/CEC: Fix pfn insertion

From: Borislav Petkov <bp@...e.de>

[ Upstream commit 6d8e294bf5f0e85c34e8b14b064e2965f53f38b0 ]

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@...e.de>
Cc: Tony Luck <tony.luck@...el.com>
Cc: linux-edac <linux-edac@...r.kernel.org>
Signed-off-by: Sasha Levin <sashal@...nel.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 f85d6b7a1984..5d2b2c02cbbe 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");
-- 
2.20.1