On Wed, Mar 22, 2023 at 4:59 PM Chuck Lever III [off-list ref] wrote:

quoted

On Mar 22, 2023, at 4:55 PM, Anna Schumaker [off-list ref] wrote:

On Wed, Mar 22, 2023 at 3:17 PM Chuck Lever [off-list ref] wrote:

quoted

From: Chuck Lever <chuck.lever@oracle.com>

Anna says:

quoted

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.

quoted

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 <redacted>
Fixes: 8270dbfcebea ("SUNRPC: Obscure Kerberos integrity keys")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

This patch fixed the issue for me, thanks! Are you going to submit it
with a future 6.3-rc pull request, or should I?

I'll queue it in nfsd-fixes.

Sounds good. Thanks!

Anna

quoted

Anna

quoted

---
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)

--
Chuck Lever