linux-kernel - [PATCH 3/3] sysctl: detect overflows when converting to int

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Date:	Sun, 29 Mar 2015 21:28:29 +0200
From:	Heinrich Schuchardt <xypron.glpk@....de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Michal Nazarewicz <mina86@...a86.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Joe Perches <joe@...ches.com>, Josh Hunt <johunt@...mai.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Daniel Walter <dwalter@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Kees Cook <keescook@...omium.org>,
	"David S. Miller" <davem@...emloft.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Aaron Tomlin <atomlin@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Eric B Munson <emunson@...mai.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Sam Ravnborg <sam@...nborg.org>, linux-kernel@...r.kernel.org,
	Heinrich Schuchardt <xypron.glpk@....de>
Subject: [PATCH 3/3] sysctl: detect overflows when converting to int

When converting unsigned long to int overflows may occur.
These currently are not detected when writing to the sysctl
file system.

E.g. on a system where int has 32 bits and long has 64 bits
  echo 0x800001234 > /proc/sys/kernel/threads-max
has the same effect as
  echo 0x1234 > /proc/sys/kernel/threads-max

The patch adds the missing check in do_proc_dointvec_conv.

With the patch an overflow will result in an error EINVAL when
writing to the the sysctl file system.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@....de>
---
 kernel/sysctl.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4d9d139..2fd6b82 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1953,7 +1953,15 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
 				 int write, void *data)
 {
 	if (write) {
-		*valp = *negp ? -*lvalp : *lvalp;
+		if (*negp) {
+			if (*lvalp > (unsigned long) INT_MAX + 1)
+				return -EINVAL;
+			*valp = -*lvalp;
+		} else {
+			if (*lvalp > (unsigned long) INT_MAX)
+				return -EINVAL;
+			*valp = *lvalp;
+		}
 	} else {
 		int val = *valp;
 		if (val < 0) {
-- 
2.1.4

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