The e1000e_write_packet_to_guest() function iterates over a set of receive descriptors by advancing rx descriptor head register (RDH) from its initial value to rx descriptor tail register (RDT). The check in e1000e_ring_empty() is responsible for detecting whether RDH has reached RDT, terminating the loop if that's the case. Additional checks have been added in the past to deal with bogus values submitted by the guest to prevent possible infinite loop. This is done by "wrapping around" RDH at some point and detecting whether it assumes the original value during the loop.
However, when e1000e is configured to use the packet split feature, RDH is incremented by two instead of one, as the packet split descriptors are 32 bytes while regular descriptors are 16 bytes. A malicious or buggy guest may set RDT to an odd value and transmit only null RX descriptors. This corner case would prevent RDH from ever matching RDT, leading to an infinite loop. This patch adds a check in e1000e_ring_advance() to make sure RDH does never exceed RDT. This issue was independently reported by Gaoning Pan (Zhejiang University) and Cheolwoo Myung. Signed-off-by: Mauro Matteo Cascella <mcasc...@redhat.com> Reported-by: Gaoning Pan <gaoning....@antgroup.com> Reported-by: Cheolwoo Myung <330cj...@gmail.com> --- References: https://git.qemu.org/?p=qemu.git;a=commit;h=dd793a74882477ca38d49e191110c17dfe https://git.qemu.org/?p=qemu.git;a=commit;h=4154c7e03fa55b4cf52509a83d50d6c09d743b7 http://www.intel.com/content/dam/doc/datasheet/82574l-gbe-controller-datasheet.pdf hw/net/e1000e_core.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/hw/net/e1000e_core.c b/hw/net/e1000e_core.c index bcd186cac5..4c4d14b6ed 100644 --- a/hw/net/e1000e_core.c +++ b/hw/net/e1000e_core.c @@ -831,6 +831,10 @@ e1000e_ring_advance(E1000ECore *core, const E1000E_RingInfo *r, uint32_t count) { core->mac[r->dh] += count; + if (core->mac[r->dh] > core->mac[r->dt]) { + core->mac[r->dh] = core->mac[r->dt]; + } + if (core->mac[r->dh] * E1000_RING_DESC_LEN >= core->mac[r->dlen]) { core->mac[r->dh] = 0; } -- 2.26.2
