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Subject[PATCH 2/2] dh key: get rid of stack array allocation
Date
Similarly to the previous patch, we would like to get rid of stack
allocated arrays: https://lkml.org/lkml/2018/3/7/621

In this case, we can also use a malloc style approach to free the temporary
buffer, being careful to also use kzfree to free them (indeed, at least one
of these has a memzero_explicit, but it seems like maybe they both
should?).

Signed-off-by: Tycho Andersen <tycho@tycho.ws>
CC: David Howells <dhowells@redhat.com>
CC: James Morris <jmorris@namei.org>
CC: "Serge E. Hallyn" <serge@hallyn.com>
---
security/keys/dh.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/security/keys/dh.c b/security/keys/dh.c
index d1ea9f325f94..f02261b24759 100644
--- a/security/keys/dh.c
+++ b/security/keys/dh.c
@@ -162,19 +162,27 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
goto err;

if (zlen && h) {
- u8 tmpbuffer[h];
+ u8 *tmpbuffer;
size_t chunk = min_t(size_t, zlen, h);
- memset(tmpbuffer, 0, chunk);
+
+ err = -ENOMEM;
+ tmpbuffer = kzalloc(chunk, GFP_KERNEL);
+ if (!tmpbuffer)
+ goto err;

do {
err = crypto_shash_update(desc, tmpbuffer,
chunk);
- if (err)
+ if (err) {
+ kzfree(tmpbuffer);
goto err;
+ }

zlen -= chunk;
chunk = min_t(size_t, zlen, h);
} while (zlen);
+
+ kzfree(tmpbuffer);
}

if (src && slen) {
@@ -184,13 +192,20 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
}

if (dlen < h) {
- u8 tmpbuffer[h];
+ u8 *tmpbuffer;
+
+ err = -ENOMEM;
+ tmpbuffer = kzalloc(h, GFP_KERNEL);
+ if (!tmpbuffer)
+ goto err;

err = crypto_shash_final(desc, tmpbuffer);
- if (err)
+ if (err) {
+ kzfree(tmpbuffer);
goto err;
+ }
memcpy(dst, tmpbuffer, dlen);
- memzero_explicit(tmpbuffer, h);
+ kzfree(tmpbuffer);
return 0;
} else {
err = crypto_shash_final(desc, dst);
--
2.15.1
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