fs/xattr.c: zero out memory copied to userspace in getxattr

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: 779302e ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Michal Hocko

fs/xattr.c

@@ -442,7 +442,7 @@ getxattr(struct dentry *d, const char __user *name, void __user *value,
 			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;