From 890e2abe1028c39e5399101a2c277219cd637aaa Mon Sep 17 00:00:00 2001
From: Tycho Andersen <tycho@tycho.ws>
Date: Tue, 24 Apr 2018 14:26:39 -0600
Subject: [PATCH] dh key: get rid of stack allocated array for zeroes
We're interested in getting rid of all of the stack allocated arrays in
the kernel: https://lkml.org/lkml/2018/3/7/621
This case is interesting, since we really just need an array of bytes that
are zero. The loop already ensures that if the array isn't exactly the
right size that enough zero bytes will be copied in. So, instead of
choosing this value to be the size of the hash, let's just choose it to be
32, since that is a common size, is not too big, and will not result in too
many extra iterations of the loop.
v2: split out from other patch, just hardcode array size instead of
dynamically allocating something the right size
v3: fix typo of 256 -> 32
Signed-off-by: Tycho Andersen <tycho@tycho.ws>
Reviewed-by: Kees Cook <keescook@chromium.org>
CC: David Howells <dhowells@redhat.com>
CC: James Morris <jmorris@namei.org>
CC: "Serge E. Hallyn" <serge@hallyn.com>
CC: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: James Morris <james.morris@microsoft.com>
---
security/keys/dh.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/security/keys/dh.c b/security/keys/dh.c
index 9fecaea6c298e..f7403821db7f0 100644
--- a/security/keys/dh.c
+++ b/security/keys/dh.c
@@ -162,8 +162,8 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
goto err;
if (zlen && h) {
- u8 tmpbuffer[h];
- size_t chunk = min_t(size_t, zlen, h);
+ u8 tmpbuffer[32];
+ size_t chunk = min_t(size_t, zlen, sizeof(tmpbuffer));
memset(tmpbuffer, 0, chunk);
do {
@@ -173,7 +173,7 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
goto err;
zlen -= chunk;
- chunk = min_t(size_t, zlen, h);
+ chunk = min_t(size_t, zlen, sizeof(tmpbuffer));
} while (zlen);
}