In the Linux kernel, the following vulnerability has been resolved:
sctp: fix NULL deref on untransmitted RECONF completion
sctp_process_strreset_outreq(), sctp_process_strreset_addstrm_out() and
sctp_process_strreset_resp() complete a pending stream reconfiguration
request by stopping the reconf timer on the transport it was sent on:
t = asoc->strreset_chunk->transport;
if (timer_delete(&t->reconf_timer))
sctp_transport_put(t);
chunk->transport is assigned by __sctp_packet_append_chunk() when the
chunk is appended to an outbound packet, and sctp_outq_flush_ctrl() arms
the reconf timer at that same point. A request already published in
asoc->strreset_chunk but not yet transmitted has neither, so completing
it dereferences NULL.
Two ways to get there. sctp_send_asconf_del_ip() sets
asoc->src_out_of_asoc_ok without sending anything when the address being
removed is the association's last one, and sctp_outq_flush_ctrl() then
leaves every non-ASCONF control chunk queued; as only
sctp_process_asconf_ack() clears that flag, it persists. An unprivileged
process that removes such an address and then asks for a stream reset
panics the kernel from softirq. A peer needs neither ASCONF nor local
help: sctp_cmd_interpreter() uncorks the outqueue only once the whole
packet has been processed, so a reply built while walking a RECONF chunk
stays untransmitted for the rest of that walk, and one RECONF chunk
carrying [Incoming SSN Reset Request, Outgoing SSN Reset Request,
Response] -- or two RECONF chunks in one packet -- reaches the same
dereference.
KASAN: null-ptr-deref in range [0x00000000000001e8-0x00000000000001ef]
RIP: 0010:timer_delete+0x67/0x110
Call Trace:
Unknown