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Date: Sat, 16 Dec 2017 00:29:09 +0000
From: Mohamed Ghannam <simo.ghannam@...il.com>
To: oss-security@...ts.openwall.com
Subject: CVE-2017-17712 net/ipv4/raw.c: raw_sendmsg() race condition
Hi,
This is an announcement for CVE-2017-17712 which is a race condition leads
to uninitialized stack variable, this might be used to gain code execution.
The bug was introduced here :
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c008ba5bdc9fa830e1a349b20b0be5a137bdef7a
And fixed here :
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8f659a03a0ba9289b9aeb9b4470e6fb263d6f483
####### BUG DETAILS ############
in net/ipv4/raw.c:
static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
...
struct raw_frag_vec rfv; [1]
...
...
if (!inet->hdrincl) { [2]
rfv.msg = msg;
rfv.hlen = 0;
err = raw_probe_proto_opt(&rfv, &fl4);
if (err)
goto done;
}
...
...
if (inet->hdrincl) [3]
err = raw_send_hdrinc(sk, &fl4, msg, len,
&rt, msg->msg_flags, &ipc.sockc);
else {
sock_tx_timestamp(sk, ipc.sockc.tsflags, &ipc.tx_flags);
if (!ipc.addr)
ipc.addr = fl4.daddr;
lock_sock(sk);
err = ip_append_data(sk, &fl4, raw_getfrag,
&rfv, len, 0, [4]
&ipc, &rt, msg->msg_flags);
...
}
[1] rfv is not initialized and contains a pointer to a msghdr header
structure.
[2], [3] There are multiple checks against inet->hdrincl without a lock.
When we achieve (by racing inet->hdrincl via setsockopt()) inet->hdrincl=1
in [1], and inet->hdrincl=0 in [2], rfv variable remains uninitialized and
used in [4].
By spraying the stack with controlled user data , we can take control of
msg pointer which is used later in ip_append_data().
In attachment : poc.c + kernel panic log
####### CREDITS ############
Mohamed GHANNAM
Content of type "text/html" skipped
Download attachment "panic.log" of type "application/octet-stream" (2899 bytes)
View attachment "poc.c" of type "text/x-csrc" (2287 bytes)
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