Hi,

On Fri, Feb 11, 2022 at 12:27:37PM +0100, Gert Doering wrote:
> the crucial part is "lsi=0x0" here, I think, but I'm not sure why... we do
> have a socket, we know we bound it to IPv6 (+dual-stack)...

Trying this trivial fix...

--- a/src/openvpn/mss.c
+++ b/src/openvpn/mss.c
@@ -234,7 +234,7 @@ get_ip_encap_overhead(const struct options *options,
 {
     /* Add the overhead of the encapsulating IP packets */
     sa_family_t af;
-    if (lsi->lsa)
+    if (lsi && lsi->lsa)
     {
         af = lsi->lsa->actual.dest.addr.sa.sa_family;
     }

... moves the crash onward to

0x00005555555891b6 in datagram_overhead (proto=<error reading variable: Cannot 
access memory at address 0x24>, af=10) at socket.h:617
617         overhead += (proto == PROTO_UDP) ? 8 : 20;
(gdb) where
#0  0x00005555555891b6 in datagram_overhead (proto=<error reading variable: 
Cannot access memory at address 0x24>, af=10) at socket.h:617
#1  get_ip_encap_overhead (lsi=0x0, options=0x555555642280) at mss.c:248
#2  frame_calculate_mssfix (lsi=0x0, options=0x555555642280, kt=0x555555642b40, 
frame=0x555555642dd0) at mss.c:305
#3  frame_calculate_dynamic (frame=frame@entry=0x555555642dd0, 
kt=kt@entry=0x555555642b40, options=options@entry=0x555555642280, lsi=0x0)
    at mss.c:334
#4  0x000055555557b2bb in init_instance (c=c@entry=0x555555642280, 
env=<optimized out>, flags=flags@entry=10) at init.c:4234
#5  0x000055555557c4a6 in inherit_context_child 
(dest=dest@entry=0x555555642280, src=src@entry=0x7fffffffc4b0) at init.c:4459

which looks weird, but is likely due to inlining.


The culprit is this one:

    return datagram_overhead(af, lsi->proto);

"lsi" is still NULL...

Not sure how to fix this in a good way.

gert

-- 
"If was one thing all people took for granted, was conviction that if you 
 feed honest figures into a computer, honest figures come out. Never doubted 
 it myself till I met a computer with a sense of humor."
                             Robert A. Heinlein, The Moon is a Harsh Mistress

Gert Doering - Munich, Germany                             [email protected]

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