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: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/xattr.c b/fs/xattr.c
index 9b932b95d74e4faeb5653d1a3c4b11553d1e51e1..f0da9d24e9ca2ed4d23980dc8c0595d7e3dcbe21 100644 (file)
--- a/fs/xattr.c
+++ b/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;