linux-kernel - [PATCH][V2][Fix commit message] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

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Message-Id: <20160916112223.32398-1-colin.king@canonical.com>
Date:   Fri, 16 Sep 2016 12:22:23 +0100
From:   Colin King <colin.king@...onical.com>
To:     Borislav Petkov <bp@...e.de>,
        Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>,
        Yazen Ghannam <Yazen.Ghannam@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH][V2][Fix commit message] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

From: Colin Ian King <colin.king@...onical.com>

Integer index i needs to be a signed int rather than unsigned to avoid
a wrap-around when decrementing in the while loop.  For example, if the
debugfs_create_file fails when i is zero, the current situation will
predecrement i in the while loop, wrapping i to the maximum signed
integer and cause multiple out of bounds reads on dfs_fls[i].d as
the loop interates to zero.

Also add (int) cast to fix warning that the original fix attempted
to fix.

Fixes: 7cc4ef8ed132 ("x86/RAS/mce_amd_inj: Fix some W= warnings")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 arch/x86/ras/mce_amd_inj.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/ras/mce_amd_inj.c b/arch/x86/ras/mce_amd_inj.c
index cd318d9..cb9779a 100644
--- a/arch/x86/ras/mce_amd_inj.c
+++ b/arch/x86/ras/mce_amd_inj.c
@@ -440,7 +440,7 @@ static struct dfs_node {
 
 static int __init init_mce_inject(void)
 {
-	unsigned int i;
+	int i;
 	u64 cap;
 
 	rdmsrl(MSR_IA32_MCG_CAP, cap);
@@ -450,7 +450,7 @@ static int __init init_mce_inject(void)
 	if (!dfs_inj)
 		return -EINVAL;
 
-	for (i = 0; i < ARRAY_SIZE(dfs_fls); i++) {
+	for (i = 0; i < (int)ARRAY_SIZE(dfs_fls); i++) {
 		dfs_fls[i].d = debugfs_create_file(dfs_fls[i].name,
 						    dfs_fls[i].perm,
 						    dfs_inj,
-- 
2.9.3