Fix modification of the received skbuff in rxrpc_input_soft_acks() and a potential incorrect access of the buffer in a fragmented UDP packet (the packet would probably have to be deliberately pre-generated as fragmented) when AF_RXRPC tries to extract the contents of the SACK table by copying out the contents of the SACK table into a buffer before attempting to parse AF_RXRPC assumes that it can just call skb_condense() and then validly access the SACK table from skb->data and that it will be a flat buffer - but skb_condense() can silently fail to do anything under some circumstances. Note that whilst rxrpc_input_soft_acks() should be able to parse extended ACKs, the rest of AF_RXRPC doesn't currently support that. Further, there's then no need to call skb_condense() in rxrpc_input_ack(), so don't. Fixes: d57a3a151660 ("rxrpc: Save last ACK's SACK table rather than marking txbufs") Reported-by: Michael Bommarito Link: https://lore.kernel.org/r/20260513180907.2061972-1-michael.bommarito@gmail.com Signed-off-by: David Howells cc: Marc Dionne cc: Jeffrey Altman cc: Eric Dumazet cc: "David S. Miller" cc: Jakub Kicinski cc: Paolo Abeni cc: Simon Horman cc: linux-afs@lists.infradead.org cc: netdev@vger.kernel.org cc: stable@kernel.org --- Changes ======= ver #2) - Fix potential overflow/infinite loop as detected by AI[1] by resetting acks pointer should the ack number hit a multiple of 256. [1] https://lore.kernel.org/r/20260521021910.687776-2-kuba@kernel.org/ net/rxrpc/input.c | 26 +++++++++++++++++--------- 1 file changed, 17 insertions(+), 9 deletions(-) diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c index 24aceb183c2c..ce761466b02d 100644 --- a/net/rxrpc/input.c +++ b/net/rxrpc/input.c @@ -963,23 +963,34 @@ static void rxrpc_input_soft_acks(struct rxrpc_call *call, struct rxrpc_skb_priv *sp = rxrpc_skb(skb); struct rxrpc_txqueue *tq = call->tx_queue; unsigned long extracted = ~0UL; - unsigned int nr = 0; + unsigned int nr = 0, nsack; rxrpc_seq_t seq = call->acks_hard_ack + 1; rxrpc_seq_t lowest_nak = seq + sp->ack.nr_acks; - u8 *acks = skb->data + sizeof(struct rxrpc_wire_header) + sizeof(struct rxrpc_ackpacket); + u8 sack[256] __aligned(sizeof(unsigned long)); + u8 *acks = sack; _enter("%x,%x,%u", tq->qbase, seq, sp->ack.nr_acks); while (after(seq, tq->qbase + RXRPC_NR_TXQUEUE - 1)) tq = tq->next; + /* Extract an individual SACK table. A normal SACK table is up to 255 + * bytes with 1 ACK flag per byte, but an extended SACK table can be up + * to 256 bytes with up to 8 ACK/NACK flags per byte. The ACK flags go + * across all bit 0's then all bit 1's, then all bit 2's, ... + */ + memset(sack, 0, sizeof(sack)); + nsack = umin(sp->ack.nr_acks, 256); + if (skb_copy_bits(skb, + sizeof(struct rxrpc_wire_header) + sizeof(struct rxrpc_ackpacket), + sack, nsack) < 0) + return; + for (unsigned int i = 0; i < sp->ack.nr_acks; i++) { /* Decant ACKs until we hit a txqueue boundary. */ + if ((i & 255) == 0) + acks = sack; shiftr_adv_rotr(acks, extracted); - if (i == 256) { - acks -= i; - i = 0; - } seq++; nr++; if ((seq & RXRPC_TXQ_MASK) != 0) @@ -1117,9 +1128,6 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb) skb_copy_bits(skb, ioffset, &trailer, sizeof(trailer)) < 0) return rxrpc_proto_abort(call, 0, rxrpc_badmsg_short_ack_trailer); - if (nr_acks > 0) - skb_condense(skb); - call->acks_latest_ts = ktime_get_real(); call->acks_hard_ack = hard_ack; call->acks_prev_seq = prev_pkt;