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

Ben Hutchings
2017-08-18T13:15:55Z

From: Michal Hocko <mhocko@suse.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@chromium.org>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.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;