From: Chuck Lever <chuck.lever@xxxxxxxxxx>
Anna says:
> KASAN reports [...] a slab-out-of-bounds in gss_krb5_checksum(),
> and it can cause my client to panic when running cthon basic
> tests with krb5p.
> Running faddr2line gives me:
>
> gss_krb5_checksum+0x4b6/0x630:
> ahash_request_free at
> /home/anna/Programs/linux-nfs.git/./include/crypto/hash.h:619
> (inlined by) gss_krb5_checksum at
> /home/anna/Programs/linux-nfs.git/net/sunrpc/auth_gss/gss_krb5_crypto.c:358
My diagnosis is that the memcpy() at the end of gss_krb5_checksum()
reads past the end of the buffer containing the checksum data
because the callers have ignored gss_krb5_checksum()'s API contract:
* Caller provides the truncation length of the output token (h) in
* cksumout.len.
Instead they provide the fixed length of the hmac buffer. This
length happens to be larger than the value returned by
crypto_ahash_digestsize().
Change these errant callers to work like krb5_etm_{en,de}crypt().
As a defensive measure, bound the length of the byte copy at the
end of gss_krb5_checksum().
Kunit sez:
Testing complete. Ran 68 tests: passed: 68
Elapsed time: 81.680s total, 5.875s configuring, 75.610s building, 0.103s running
Reported-by: Anna Schumaker <schumaker.anna@xxxxxxxxx>
Fixes: 8270dbfcebea ("SUNRPC: Obscure Kerberos integrity keys")
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
net/sunrpc/auth_gss/gss_krb5_crypto.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
index 6c7c52eeed4f..212c5d57465a 100644
--- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
+++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
@@ -353,7 +353,9 @@ gss_krb5_checksum(struct crypto_ahash *tfm, char *header, int hdrlen,
err = crypto_ahash_final(req);
if (err)
goto out_free_ahash;
- memcpy(cksumout->data, checksumdata, cksumout->len);
+
+ memcpy(cksumout->data, checksumdata,
+ min_t(int, cksumout->len, crypto_ahash_digestsize(tfm)));
out_free_ahash:
ahash_request_free(req);
@@ -809,8 +811,7 @@ gss_krb5_aes_encrypt(struct krb5_ctx *kctx, u32 offset,
buf->tail[0].iov_len += GSS_KRB5_TOK_HDR_LEN;
buf->len += GSS_KRB5_TOK_HDR_LEN;
- /* Do the HMAC */
- hmac.len = GSS_KRB5_MAX_CKSUM_LEN;
+ hmac.len = kctx->gk5e->cksumlength;
hmac.data = buf->tail[0].iov_base + buf->tail[0].iov_len;
/*
@@ -873,8 +874,7 @@ gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, u32 len,
if (ret)
goto out_err;
- /* Calculate our hmac over the plaintext data */
- our_hmac_obj.len = sizeof(our_hmac);
+ our_hmac_obj.len = kctx->gk5e->cksumlength;
our_hmac_obj.data = our_hmac;
ret = gss_krb5_checksum(ahash, NULL, 0, &subbuf, 0, &our_hmac_obj);
if (ret)
