Subject: Re: [PATCH 2/2] sctp: hold cached endpoints to prevent possible UAF

From: Lee Jones <[email-masked]>
Date: Wed, 15 Dec 2021 06:49:30 +0000

On Tue, 14 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 followed by an endpoint/sock migration to a new
> association in sctp_assoc_migrate() prior to their subsequent use in
> sctp_diag_dump() which uses sctp_for_each_transport() to walk the hash
> table calling into sctp_sock_dump() where the dereference occurs.
> 
>   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
> 
> To prevent this from happening we need to take a references to the
> to-be-used/dereferenced 'struct sock' and 'struct sctp_endpoint's
> 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.
> 
> Cc: Vlad Yasevich <[email-masked]>
> Cc: Neil Horman <[email-masked]>
> Cc: Marcelo Ricardo Leitner <[email-masked]>
> Cc: "David S. Miller" <[email-masked]>
> Cc: Jakub Kicinski <[email-masked]>
> Cc: lksctp developers <[email-masked]>
> Cc: "H.P. Yarroll" <[email-masked]>
> Cc: Karl Knutson <[email-masked]>
> Cc: Jon Grimm <[email-masked]>
> Cc: Xingang Guo <[email-masked]>
> Cc: Hui Huang <[email-masked]>
> Cc: Sridhar Samudrala <[email-masked]>
> Cc: Daisy Chang <[email-masked]>
> Cc: Ryan Layer <[email-masked]>
> Cc: Kevin Gao <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Signed-off-by: Lee Jones <[email-masked]>
> ---
>  net/sctp/diag.c | 4 ++++
>  1 file changed, 4 insertions(+)

Ignore this one.  For some reason 1/2 didn't send.

Submitted a RESEND of the set.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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