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net: pad packets to minimum length in qemu_receive_packet()

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In commits like 969e50b61a ("net: Pad short frames to minimum size
before sending from SLiRP/TAP") we switched away from requiring
network devices to handle short frames to instead having the net core
code do the padding of short frames out to the ETH_ZLEN minimum size.
We then dropped the code for handling short frames from the network
devices in a series of commits like 140eae9c8f ("hw/net: e1000:
Remove the logic of padding short frames in the receive path").

This missed one route where the device's receive code can still see a
short frame: if the device is in loopback mode and it transmits a
short frame via the qemu_receive_packet() function, this will be fed
back into its own receive code without being padded.

Add the padding logic to qemu_receive_packet().

This fixes a buffer overrun which can be triggered in the
e1000_receive_iov() logic via the loopback code path.

Other devices that use qemu_receive_packet() to implement loopback
are cadence_gem, dp8393x, lan9118, msf2-emac, pcnet, rtl8139
and sungem.

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3043
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>
This commit is contained in:
Peter Maydell 2025-10-28 16:00:42 +00:00 • committed by Jason Wang
parent bab496a183
commit a01344d9d7
1 changed files with 10 additions and 0 deletions
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10
net/net.c
View file

@ -775,10 +775,20 @@ ssize_t qemu_send_packet(NetClientState *nc, const uint8_t *buf, int size)
ssize_t qemu_receive_packet(NetClientState *nc, const uint8_t *buf, int size) ssize_t qemu_receive_packet(NetClientState *nc, const uint8_t *buf, int size)
{ {
uint8_t min_pkt[ETH_ZLEN];
size_t min_pktsz = sizeof(min_pkt);
if (!qemu_can_receive_packet(nc)) { if (!qemu_can_receive_packet(nc)) {
return 0; return 0;
} }
if (net_peer_needs_padding(nc)) {
if (eth_pad_short_frame(min_pkt, &min_pktsz, buf, size)) {
buf = min_pkt;
size = min_pktsz;
}
}
return qemu_net_queue_receive(nc->incoming_queue, buf, size); return qemu_net_queue_receive(nc->incoming_queue, buf, size);
} }