* [PATCH net v3 2/4] crypto/krb5, rxrpc: Fix lack of pre-decrypt/pre-verify length checks
[not found] <20260514155304.2249591-1-dhowells@redhat.com>
@ 2026-05-14 15:53 ` David Howells
0 siblings, 0 replies; only message in thread
From: David Howells @ 2026-05-14 15:53 UTC (permalink / raw)
To: netdev
Cc: David Howells, Hyunwoo Kim, Marc Dionne, Jakub Kicinski,
David S. Miller, Eric Dumazet, Paolo Abeni, Simon Horman,
linux-afs, linux-kernel, Jeffrey Altman, Herbert Xu, Chuck Lever,
linux-nfs, linux-crypto, stable
Change the krb5 crypto library to provide facilities to precheck the length
of the message about to be decrypted or verified.
Fix AF_RXRPC to make use of this to validate DATA packets secured with
RxGK.
Fixes: 9d1d2b59341f ("rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)")
Closes: https://sashiko.dev/#/patchset/20260511160753.607296-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: netdev@vger.kernel.org
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-crypto@vger.kernel.org
cc: stable@vger.kernel.org
---
Documentation/crypto/krb5.rst | 17 ++++++++---
crypto/krb5/krb5_api.c | 54 +++++++++++++++++++++++++++++++----
include/crypto/krb5.h | 9 ++++--
include/trace/events/rxrpc.h | 1 +
net/rxrpc/rxgk.c | 15 ++++++++--
5 files changed, 81 insertions(+), 15 deletions(-)
diff --git a/Documentation/crypto/krb5.rst b/Documentation/crypto/krb5.rst
index beffa0133446..f62e07ac6811 100644
--- a/Documentation/crypto/krb5.rst
+++ b/Documentation/crypto/krb5.rst
@@ -158,13 +158,22 @@ returned.
When a message has been received, the location and size of the data with the
message can be determined by calling::
- void crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
- enum krb5_crypto_mode mode,
- size_t *_offset, size_t *_len);
+ int crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
+ enum krb5_crypto_mode mode,
+ size_t *_offset, size_t *_len);
The caller provides the offset and length of the message to the function, which
then alters those values to indicate the region containing the data (plus any
-padding). It is up to the caller to determine how much padding there is.
+padding). It is up to the caller to determine how much padding there is. The
+function returns an error if the length is too small or if the mode is
+unsupported. An additional function::
+
+ int crypto_krb5_check_data_len(const struct krb5_enctype *krb5,
+ enum krb5_crypto_mode mode,
+ size_t len, size_t min_content);
+
+is provided to just do a basic check that the decrypted/verified message would
+have a sufficient minimum payload.
Preparation Functions
---------------------
diff --git a/crypto/krb5/krb5_api.c b/crypto/krb5/krb5_api.c
index 23026d4206c8..c7ea40f900a7 100644
--- a/crypto/krb5/krb5_api.c
+++ b/crypto/krb5/krb5_api.c
@@ -134,27 +134,69 @@ EXPORT_SYMBOL(crypto_krb5_how_much_data);
* Find the offset and size of the data in a secure message so that this
* information can be used in the metadata buffer which will get added to the
* digest by crypto_krb5_verify_mic().
+ *
+ * Return: 0 if successful, -EBADMSG if the message is too short or -EINVAL if
+ * the mode is unsupported.
*/
-void crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
- enum krb5_crypto_mode mode,
- size_t *_offset, size_t *_len)
+int crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
+ enum krb5_crypto_mode mode,
+ size_t *_offset, size_t *_len)
{
switch (mode) {
case KRB5_CHECKSUM_MODE:
+ if (*_len < krb5->cksum_len)
+ return -EBADMSG;
*_offset += krb5->cksum_len;
*_len -= krb5->cksum_len;
- return;
+ return 0;
case KRB5_ENCRYPT_MODE:
+ if (*_len < krb5->conf_len + krb5->cksum_len)
+ return -EBADMSG;
*_offset += krb5->conf_len;
*_len -= krb5->conf_len + krb5->cksum_len;
- return;
+ return 0;
default:
WARN_ON_ONCE(1);
- return;
+ return -EINVAL;
}
}
EXPORT_SYMBOL(crypto_krb5_where_is_the_data);
+/**
+ * crypto_krb5_check_data_len - Check a message is big enough
+ * @krb5: The encoding to use.
+ * @mode: Mode of operation.
+ * @len: The length of the secure blob.
+ * @min_content: Minimum length of the content inside the blob.
+ *
+ * Check that a message is large enough to hold whatever bits the encryption
+ * type wants to glue on (nonce, checksum) plus a minimum amount of content.
+ *
+ * Return: 0 if successful, -EBADMSG if the message is too short or -EINVAL if
+ * the mode is unsupported.
+ */
+int crypto_krb5_check_data_len(const struct krb5_enctype *krb5,
+ enum krb5_crypto_mode mode,
+ size_t len, size_t min_content)
+{
+ switch (mode) {
+ case KRB5_CHECKSUM_MODE:
+ if (len < krb5->cksum_len ||
+ len - krb5->cksum_len < min_content)
+ return -EBADMSG;
+ return 0;
+ case KRB5_ENCRYPT_MODE:
+ if (len < krb5->conf_len + krb5->cksum_len ||
+ len - (krb5->conf_len + krb5->cksum_len) < min_content)
+ return -EBADMSG;
+ return 0;
+ default:
+ WARN_ON_ONCE(1);
+ return -EINVAL;
+ }
+}
+EXPORT_SYMBOL(crypto_krb5_check_data_len);
+
/*
* Prepare the encryption with derived key data.
*/
diff --git a/include/crypto/krb5.h b/include/crypto/krb5.h
index 71dd38f59be1..aac3ecf88467 100644
--- a/include/crypto/krb5.h
+++ b/include/crypto/krb5.h
@@ -121,9 +121,12 @@ size_t crypto_krb5_how_much_buffer(const struct krb5_enctype *krb5,
size_t crypto_krb5_how_much_data(const struct krb5_enctype *krb5,
enum krb5_crypto_mode mode,
size_t *_buffer_size, size_t *_offset);
-void crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
- enum krb5_crypto_mode mode,
- size_t *_offset, size_t *_len);
+int crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
+ enum krb5_crypto_mode mode,
+ size_t *_offset, size_t *_len);
+int crypto_krb5_check_data_len(const struct krb5_enctype *krb5,
+ enum krb5_crypto_mode mode,
+ size_t len, size_t min_content);
struct crypto_aead *crypto_krb5_prepare_encryption(const struct krb5_enctype *krb5,
const struct krb5_buffer *TK,
u32 usage, gfp_t gfp);
diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 573f2df3a2c9..704a10de6670 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -71,6 +71,7 @@
EM(rxkad_abort_resp_unknown_tkt, "rxkad-resp-unknown-tkt") \
EM(rxkad_abort_resp_version, "rxkad-resp-version") \
/* RxGK security errors */ \
+ EM(rxgk_abort_1_short_header, "rxgk1-short-hdr") \
EM(rxgk_abort_1_verify_mic_eproto, "rxgk1-vfy-mic-eproto") \
EM(rxgk_abort_2_decrypt_eproto, "rxgk2-dec-eproto") \
EM(rxgk_abort_2_short_data, "rxgk2-short-data") \
diff --git a/net/rxrpc/rxgk.c b/net/rxrpc/rxgk.c
index 0d5e654da918..26e723052a37 100644
--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -480,8 +480,12 @@ static int rxgk_verify_packet_integrity(struct rxrpc_call *call,
_enter("");
- crypto_krb5_where_is_the_data(gk->krb5, KRB5_CHECKSUM_MODE,
- &data_offset, &data_len);
+ if (crypto_krb5_where_is_the_data(gk->krb5, KRB5_CHECKSUM_MODE,
+ &data_offset, &data_len) < 0) {
+ ret = rxrpc_abort_eproto(call, skb, RXGK_PACKETSHORT,
+ rxgk_abort_1_short_header);
+ goto put_gk;
+ }
hdr = kzalloc_obj(*hdr, GFP_NOFS);
if (!hdr)
@@ -529,6 +533,13 @@ static int rxgk_verify_packet_encrypted(struct rxrpc_call *call,
_enter("");
+ if (crypto_krb5_check_data_len(gk->krb5, KRB5_ENCRYPT_MODE,
+ len, sizeof(hdr)) < 0) {
+ ret = rxrpc_abort_eproto(call, skb, RXGK_PACKETSHORT,
+ rxgk_abort_2_short_header);
+ goto error;
+ }
+
ret = rxgk_decrypt_skb(gk->krb5, gk->rx_enc, skb, &offset, &len, &ac);
if (ret < 0) {
if (ret != -ENOMEM)
^ permalink raw reply related [flat|nested] only message in thread