> On Mar 22, 2023, at 4:55 PM, Anna Schumaker <schumaker.anna@xxxxxxxxx> wrote:
>
> On Wed, Mar 22, 2023 at 3:17 PM Chuck Lever <cel@xxxxxxxxxx> wrote:
>>
>> 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>
>
> 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.
> Anna
>
>> ---
>> 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
