[CVE-2017-7616][PATCH Trusty] mm/mempolicy.c: fix error handling in set_mempolicy and mbind.

[Po-Hsu Lin]

From: Chris Salls <salls at cs.ucsb.edu>

CVE-2017-7616

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 at cs.ucsb.edu>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit cf01fb9985e8deb25ccf0ea54d916b8871ae0e62)
Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
---
 mm/mempolicy.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 5990620..c5802e4 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1590,7 +1590,6 @@ asmlinkage long compat_sys_get_mempolicy(int __user *policy,
 asmlinkage long compat_sys_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);
@@ -1599,14 +1598,13 @@ asmlinkage long compat_sys_set_mempolicy(int mode, compat_ulong_t __user *nmask,
 	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);
 }
 
@@ -1614,7 +1612,6 @@ asmlinkage long compat_sys_mbind(compat_ulong_t start, compat_ulong_t len,
 			     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;
@@ -1623,14 +1620,13 @@ asmlinkage long compat_sys_mbind(compat_ulong_t start, compat_ulong_t len,
 	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);
 }
 
-- 
2.7.4