[PATCH net] rxrpc: Fix untrusted unsigned subtract
From: David Howells <dhowells@redhat.com>
Date: 2025-09-11 23:06:27
Also in:
lkml
Subsystem:
networking [general], rxrpc sockets (af_rxrpc), the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Howells, Marc Dionne, Linus Torvalds
Fix the following Smatch Smatch static checker warning:
net/rxrpc/rxgk_app.c:65 rxgk_yfs_decode_ticket()
warn: untrusted unsigned subtract. 'ticket_len - 10 * 4'
by prechecking the length of what we're trying to extract in two places in
the token and decoding for a response packet.
Also use sizeof() on the struct we're extracting rather specifying the size
numerically to be consistent with the other related statements.
Fixes: 9d1d2b59341f ("rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)")
Reported-by: Dan Carpenter <redacted>
Closes: https://lists.infradead.org/pipermail/linux-afs/2025-September/010135.html
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
---
net/rxrpc/rxgk_app.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/net/rxrpc/rxgk_app.c b/net/rxrpc/rxgk_app.c
index df684b5a8531..30275cb5ba3e 100644
--- a/net/rxrpc/rxgk_app.c
+++ b/net/rxrpc/rxgk_app.c@@ -54,6 +54,10 @@ int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb, _enter(""); + if (ticket_len < 10 * sizeof(__be32)) + return rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO, + rxgk_abort_resp_short_yfs_tkt); + /* Get the session key length */ ret = skb_copy_bits(skb, ticket_offset, tmp, sizeof(tmp)); if (ret < 0)
@@ -195,22 +199,23 @@ int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb, __be32 token_len; } container; + if (token_len < sizeof(container)) + goto short_packet; + /* Decode the RXGK_TokenContainer object. This tells us which server * key we should be using. We can then fetch the key, get the secret * and set up the crypto to extract the token. */ if (skb_copy_bits(skb, token_offset, &container, sizeof(container)) < 0) - return rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO, - rxgk_abort_resp_tok_short); + goto short_packet; kvno = ntohl(container.kvno); enctype = ntohl(container.enctype); ticket_len = ntohl(container.token_len); ticket_offset = token_offset + sizeof(container); - if (xdr_round_up(ticket_len) > token_len - 3 * 4) - return rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO, - rxgk_abort_resp_tok_short); + if (xdr_round_up(ticket_len) > token_len - sizeof(container)) + goto short_packet; _debug("KVNO %u", kvno); _debug("ENC %u", enctype);
@@ -285,4 +290,8 @@ int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb, * also come out this way if the ticket decryption fails. */ return ret; + +short_packet: + return rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO, + rxgk_abort_resp_tok_short); }