Re: [PATCH 1/1] sctp: Protect cached endpoints to prevent possible UAF

[Marcelo Ricardo Leitner]

On Wed, Dec 08, 2021 at 05:02:12PM +0000, Lee Jones wrote:
> On Wed, 08 Dec 2021, Lee Jones wrote:
> 
> > The cause of the resultant dump_stack() reported below is a
> > dereference of a freed pointer to 'struct sctp_endpoint' in
> > sctp_sock_dump().
> > 
> > This race condition occurs when a transport is cached into its
> > associated hash table then freed prior to its subsequent use in
> > sctp_diag_dump() which uses sctp_for_each_transport() to walk the
> > (now out of date) hash table calling into sctp_sock_dump() where the
> > dereference occurs.
> > 
> > To prevent this from happening we need to take a reference on the
> > to-be-used/dereferenced 'struct sctp_endpoint' until such a time when
> > we know it can be safely released.
> > 
> > When KASAN is not enabled, a similar, but slightly different NULL
> > pointer derefernce crash occurs later along the thread of execution in
> > inet_sctp_diag_fill() this time.
> > 
> >   BUG: KASAN: use-after-free in sctp_sock_dump+0xa8/0x438 [sctp_diag]
> >   Call trace:
> >    dump_backtrace+0x0/0x2dc
> >    show_stack+0x20/0x2c
> >    dump_stack+0x120/0x144
> >    print_address_description+0x80/0x2f4
> >    __kasan_report+0x174/0x194
> >    kasan_report+0x10/0x18
> >    __asan_load8+0x84/0x8c
> >    sctp_sock_dump+0xa8/0x438 [sctp_diag]
> >    sctp_for_each_transport+0x1e0/0x26c [sctp]
> >    sctp_diag_dump+0x180/0x1f0 [sctp_diag]
> >    inet_diag_dump+0x12c/0x168
> >    netlink_dump+0x24c/0x5b8
> >    __netlink_dump_start+0x274/0x2a8
> >    inet_diag_handler_cmd+0x224/0x274
> >    sock_diag_rcv_msg+0x21c/0x230
> >    netlink_rcv_skb+0xe0/0x1bc
> >    sock_diag_rcv+0x34/0x48
> >    netlink_unicast+0x3b4/0x430
> >    netlink_sendmsg+0x4f0/0x574
> >    sock_write_iter+0x18c/0x1f0
> >    do_iter_readv_writev+0x230/0x2a8
> >    do_iter_write+0xc8/0x2b4
> >    vfs_writev+0xf8/0x184
> >    do_writev+0xb0/0x1a8
> >    __arm64_sys_writev+0x4c/0x5c
> >    el0_svc_common+0x118/0x250
> >    el0_svc_handler+0x3c/0x9c
> >    el0_svc+0x8/0xc
> 
> This looks related (reported 3 years ago!)
> 
>   https://lore.kernel.org/all/20181122131344.GD31918@localhost.localdomain/

Agree, seems related. Thanks for root causing it.