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tcp: Avoid overlapping memcpy() in DUP_ACK handling

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When handling the DUP_ACK flag, we copy all the buffers making up the ack
frame.  However, all our frames share the same buffer for the Ethernet
header (tcp4_eth_src or tcp6_eth_src), so copying the TCP_IOV_ETH will
result in a (perfectly) overlapping memcpy().  This seems to have been
harmless so far, but overlapping ranges to memcpy() is undefined behaviour,
so we really should avoid it.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2024-09-12 16:59:40 +10:00 committed by Stefano Brivio
parent 1f414ed8f0
commit 5ff5d55291
1 changed files with 7 additions and 3 deletions
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6
tcp_buf.c
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@ -332,9 +332,13 @@ int tcp_buf_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
else
dup_iov = tcp6_l2_flags_iov[tcp6_flags_used++];
for (i = 0; i < TCP_NUM_IOVS; i++)
for (i = 0; i < TCP_NUM_IOVS; i++) {
/* All frames share the same ethernet header buffer */
if (i != TCP_IOV_ETH) {
memcpy(dup_iov[i].iov_base, iov[i].iov_base,
iov[i].iov_len);
}
}
dup_iov[TCP_IOV_PAYLOAD].iov_len = iov[TCP_IOV_PAYLOAD].iov_len;
}