linux-kernel - [PATCH 3.16 194/212] mm/mempolicy.c: fix error handling in set

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Message-ID: <lsq.1496331796.85572069@decadent.org.uk>
Date:   Thu, 01 Jun 2017 16:43:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Chris Salls" <salls@...ucsb.edu>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 194/212] mm/mempolicy.c: fix error handling in
 set_mempolicy and mbind.

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Salls <salls@...ucsb.edu>

commit cf01fb9985e8deb25ccf0ea54d916b8871ae0e62 upstream.

In the case that compat_get_bitmap fails we do not want to copy the
bitmap to the user as it will contain uninitialized stack data and leak
sensitive data.

Signed-off-by: Chris Salls <salls@...ucsb.edu>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/mempolicy.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1559,7 +1559,6 @@ COMPAT_SYSCALL_DEFINE5(get_mempolicy, in
 COMPAT_SYSCALL_DEFINE3(set_mempolicy, int, mode, compat_ulong_t __user *, nmask,
 		       compat_ulong_t, maxnode)
 {
-	long err = 0;
 	unsigned long __user *nm = NULL;
 	unsigned long nr_bits, alloc_size;
 	DECLARE_BITMAP(bm, MAX_NUMNODES);
@@ -1568,14 +1567,13 @@ COMPAT_SYSCALL_DEFINE3(set_mempolicy, in
 	alloc_size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
 
 	if (nmask) {
-		err = compat_get_bitmap(bm, nmask, nr_bits);
+		if (compat_get_bitmap(bm, nmask, nr_bits))
+			return -EFAULT;
 		nm = compat_alloc_user_space(alloc_size);
-		err |= copy_to_user(nm, bm, alloc_size);
+		if (copy_to_user(nm, bm, alloc_size))
+			return -EFAULT;
 	}
 
-	if (err)
-		return -EFAULT;
-
 	return sys_set_mempolicy(mode, nm, nr_bits+1);
 }
 
@@ -1583,7 +1581,6 @@ COMPAT_SYSCALL_DEFINE6(mbind, compat_ulo
 		       compat_ulong_t, mode, compat_ulong_t __user *, nmask,
 		       compat_ulong_t, maxnode, compat_ulong_t, flags)
 {
-	long err = 0;
 	unsigned long __user *nm = NULL;
 	unsigned long nr_bits, alloc_size;
 	nodemask_t bm;
@@ -1592,14 +1589,13 @@ COMPAT_SYSCALL_DEFINE6(mbind, compat_ulo
 	alloc_size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
 
 	if (nmask) {
-		err = compat_get_bitmap(nodes_addr(bm), nmask, nr_bits);
+		if (compat_get_bitmap(nodes_addr(bm), nmask, nr_bits))
+			return -EFAULT;
 		nm = compat_alloc_user_space(alloc_size);
-		err |= copy_to_user(nm, nodes_addr(bm), alloc_size);
+		if (copy_to_user(nm, nodes_addr(bm), alloc_size))
+			return -EFAULT;
 	}
 
-	if (err)
-		return -EFAULT;
-
 	return sys_mbind(start, len, mode, nm, nr_bits+1, flags);
 }