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From e265c8d4c039729f2a68f3b1fb589c13c38d86f8 Mon Sep 17 00:00:00 2001
From: Russ Dill <russ.dill@gmail.com>
Date: Mon, 2 Oct 2023 12:34:50 -0700
Subject: [PATCH] udhcp: Avoid leaking uninitialized/stale data
I noticed a commit in connman:
"gdhcp: Avoid leaking stack data via unitiialized variable" [1]
Since gdhcp is just BusyBox udhcp with the serial numbers filed off, I
checked if BusyBox udhcp has a related issue.
The issue is that the get_option logic assumes any data within the
memory area of the buffer is "valid". This reduces the complexity of the
function at the cost of reading past the end of the actually received
data in the case of specially crafted packets. This is not a problem
for the udhcp_recv_kernel_packet data path as the entire memory
area is zeroed. However, d4/d6_recv_raw_packet does not zero the
memory.
Note that a related commit [2] is not required as we are zeroing
any data that can be read by the get_option function.
[1] https://git.kernel.org/pub/scm/network/connman/connman.git/commit/?id=a74524b3e3fad81b0fd1084ffdf9f2ea469cd9b1
[2] https://git.kernel.org/pub/scm/network/connman/connman.git/commit/?id=58d397ba74873384aee449690a9070bacd5676fa
function old new delta
d4_recv_raw_packet 484 497 +13
d6_recv_raw_packet 216 228 +12
.rodata 105390 105381 -9
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 25/-9) Total: 16 bytes
Signed-off-by: Russ Dill <russ.dill@gmail.com>
Cc: Colin Wee <cwee@tesla.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---
networking/udhcp/d6_dhcpc.c | 1 +
networking/udhcp/dhcpc.c | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/networking/udhcp/d6_dhcpc.c b/networking/udhcp/d6_dhcpc.c
index cdd06188e..a72fd31bd 100644
--- a/networking/udhcp/d6_dhcpc.c
+++ b/networking/udhcp/d6_dhcpc.c
@@ -961,6 +961,7 @@ static NOINLINE int d6_recv_raw_packet(struct in6_addr *peer_ipv6, struct d6_pac
d6_dump_packet(&packet.data);
bytes -= sizeof(packet.ip6) + sizeof(packet.udp);
+ memset(d6_pkt, 0, sizeof(*d6_pkt));
memcpy(d6_pkt, &packet.data, bytes);
return bytes;
}
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 200a2fb8a..07e2eadfe 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -966,7 +966,7 @@ static NOINLINE int d4_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
check = packet.udp.check;
packet.udp.check = 0;
if (check && check != inet_cksum(&packet, bytes)) {
- log1s("packet with bad UDP checksum received, ignoring");
+ log1s("packet with bad UDP checksum, ignoring");
return -2;
}
skip_udp_sum_check:
@@ -981,6 +981,7 @@ static NOINLINE int d4_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
udhcp_dump_packet(&packet.data);
bytes -= sizeof(packet.ip) + sizeof(packet.udp);
+ memset(dhcp_pkt, 0, sizeof(*dhcp_pkt));
memcpy(dhcp_pkt, &packet.data, bytes);
return bytes;
}
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