Commit 890e2abe authored Apr 24, 2018 by Tycho Andersen Committed by James Morris May 11, 2018

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>

parent 383203ef

security/keys/dh.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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);
		}

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