linux-kernel - [PATCH] sysctl: Fix conversion of INT

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Message-Id: <201507110735.t6B7ZeLR004574@smtp02.srv.cs.cmu.edu>
Date:	Sat, 11 Jul 2015 00:35:44 -0700
From:	Robert Xiao <brx@...cmu.edu>
To:	"LKML <linux-kernel@...r.kernel.org>; Mikulas Patocka
	<mikulas@...bright.com>; Ilya Dryomov <idryomov@...il.com>; Robert Xiao
	<brx@...cmu.edu>; Robert Xiao" <nneonneo@...il.com>
Cc:	Robert Xiao <brx@...cmu.edu>
Subject: [PATCH] sysctl: Fix conversion of INT_MIN for LP64 systems

On LP64 systems, reading a sysctl file containing an INT_MIN (-2147483648)
could incorrectly show -18446744071562067968 due to an incorrect conversion
in do_proc_dointvec_conv. This patch fixes the edge case by converting to
unsigned int first to avoid sign extending INT_MIN to unsigned long.

Test:

root:/proc/sys/kernel# echo -2147483648 0 0 0 > printk
root:/proc/sys/kernel# cat printk

Without patch, produces -18446744071562067968 0 0 0.
With patch, should produce -2147483648 0 0 0.

Signed-off-by: Robert Xiao <brx@...cmu.edu>
---
 kernel/sysctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 19b62b5..464df36 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1995,10 +1995,10 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
 		int val = *valp;
 		if (val < 0) {
 			*negp = true;
-			*lvalp = (unsigned long)-val;
+			*lvalp = (unsigned int)-val;
 		} else {
 			*negp = false;
-			*lvalp = (unsigned long)val;
+			*lvalp = (unsigned int)val;
 		}
 	}
 	return 0;
-- 
2.2.2
--
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