linux-kernel - [PATCH 3.16 120/134] fs/xattr.c: zero out memory copied to userspace in getxattr

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Message-ID: <lsq.1503062000.555597719@decadent.org.uk>
Date:   Fri, 18 Aug 2017 14:13:20 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Michal Hocko" <mhocko@...e.com>,
        "Kees Cook" <keescook@...omium.org>,
        "Vlastimil Babka" <vbabka@...e.cz>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 120/134] fs/xattr.c: zero out memory copied to
 userspace in getxattr

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

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

From: Michal Hocko <mhocko@...e.com>

commit 81be3dee96346fbe08c31be5ef74f03f6b63cf68 upstream.

getxattr uses vmalloc to allocate memory if kzalloc fails.  This is
filled by vfs_getxattr and then copied to the userspace.  vmalloc,
however, doesn't zero out the memory so if the specific implementation
of the xattr handler is sloppy we can theoretically expose a kernel
memory.  There is no real sign this is really the case but let's make
sure this will not happen and use vzalloc instead.

Fixes: 779302e67835 ("fs/xattr.c:getxattr(): improve handling of allocation failures")
Link: http://lkml.kernel.org/r/20170306103327.2766-1-mhocko@kernel.org
Acked-by: Kees Cook <keescook@...omium.org>
Reported-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/xattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -455,7 +455,7 @@ getxattr(struct dentry *d, const char __
 			size = XATTR_SIZE_MAX;
 		kvalue = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
 		if (!kvalue) {
-			vvalue = vmalloc(size);
+			vvalue = vzalloc(size);
 			if (!vvalue)
 				return -ENOMEM;
 			kvalue = vvalue;