linux-kernel - [PATCH][V3] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

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Message-Id: <20160917101750.6436-1-colin.king@canonical.com>
Date:   Sat, 17 Sep 2016 11:17:50 +0100
From:   Colin King <colin.king@...onical.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        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][V3] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

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

Change predecrement compare to post decrement compare to avoid an
unsigned integer wrap-around comparisomn 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, as Borislav Petkov suggested, return -ENODEV rather than -ENOMEM
on the error condition.

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..20b227f 100644
--- a/arch/x86/ras/mce_amd_inj.c
+++ b/arch/x86/ras/mce_amd_inj.c
@@ -464,13 +464,13 @@ static int __init init_mce_inject(void)
 	return 0;
 
 err_dfs_add:
-	while (--i >= 0)
+	while (i-- > 0)
 		debugfs_remove(dfs_fls[i].d);
 
 	debugfs_remove(dfs_inj);
 	dfs_inj = NULL;
 
-	return -ENOMEM;
+	return -ENODEV;
 }
 
 static void __exit exit_mce_inject(void)
-- 
2.9.3