[PATCH] rxrpc: fix some null-ptr-deref bugs in server_key.c

[Marc Dionne]

On Tue, Mar 22, 2022 at 1:28 PM Xiaolong Huang
<butterflyhuangxx at gmail.com> wrote:
>
> Some function calls are not implemented in rxrpc_no_security, there are
> preparse_server_key, free_preparse_server_key and destroy_server_key.
> When rxrpc security type is rxrpc_no_security, user can easily trigger a
> null-ptr-deref bug via ioctl. So judgment should be added to prevent it
>
> The crash log:
> user at syzkaller:~$ ./rxrpc_preparse_s
> [   37.956878][T15626] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [   37.957645][T15626] #PF: supervisor instruction fetch in kernel mode
> [   37.958229][T15626] #PF: error_code(0x0010) - not-present page
> [   37.958762][T15626] PGD 4aadf067 P4D 4aadf067 PUD 4aade067 PMD 0
> [   37.959321][T15626] Oops: 0010 [#1] PREEMPT SMP
> [   37.959739][T15626] CPU: 0 PID: 15626 Comm: rxrpc_preparse_ Not tainted 5.17.0-01442-gb47d5a4f6b8d #43
> [   37.960588][T15626] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
> [   37.961474][T15626] RIP: 0010:0x0
> [   37.961787][T15626] Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
> [   37.962480][T15626] RSP: 0018:ffffc9000d9abdc0 EFLAGS: 00010286
> [   37.963018][T15626] RAX: ffffffff84335200 RBX: ffff888012a1ce80 RCX: 0000000000000000
> [   37.963727][T15626] RDX: 0000000000000000 RSI: ffffffff84a736dc RDI: ffffc9000d9abe48
> [   37.964425][T15626] RBP: ffffc9000d9abe48 R08: 0000000000000000 R09: 0000000000000002
> [   37.965118][T15626] R10: 000000000000000a R11: f000000000000000 R12: ffff888013145680
> [   37.965836][T15626] R13: 0000000000000000 R14: ffffffffffffffec R15: ffff8880432aba80
> [   37.966441][T15626] FS:  00007f2177907700(0000) GS:ffff88803ec00000(0000) knlGS:0000000000000000
> [   37.966979][T15626] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   37.967384][T15626] CR2: ffffffffffffffd6 CR3: 000000004aaf1000 CR4: 00000000000006f0
> [   37.967864][T15626] Call Trace:
> [   37.968062][T15626]  <TASK>
> [   37.968240][T15626]  rxrpc_preparse_s+0x59/0x90
> [   37.968541][T15626]  key_create_or_update+0x174/0x510
> [   37.968863][T15626]  __x64_sys_add_key+0x139/0x1d0
> [   37.969165][T15626]  do_syscall_64+0x35/0xb0
> [   37.969451][T15626]  entry_SYSCALL_64_after_hwframe+0x44/0xae
> [   37.969824][T15626] RIP: 0033:0x43a1f9
>
> Signed-off-by: Xiaolong Huang <butterflyhuangxx at gmail.com>
> Tested-by: Xiaolong Huang <butterflyhuangxx at gmail.com>
> ---
>  net/rxrpc/server_key.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/net/rxrpc/server_key.c b/net/rxrpc/server_key.c
> index ead3471307ee..ee269e0e6ee8 100644
> --- a/net/rxrpc/server_key.c
> +++ b/net/rxrpc/server_key.c
> @@ -84,6 +84,9 @@ static int rxrpc_preparse_s(struct key_preparsed_payload *prep)
>
>         prep->payload.data[1] = (struct rxrpc_security *)sec;
>
> +       if (!sec->preparse_server_key)
> +               return -EINVAL;
> +
>         return sec->preparse_server_key(prep);
>  }
>
> @@ -91,7 +94,7 @@ static void rxrpc_free_preparse_s(struct key_preparsed_payload *prep)
>  {
>         const struct rxrpc_security *sec = prep->payload.data[1];
>
> -       if (sec)
> +       if (sec && sec->free_preparse_server_key)
>                 sec->free_preparse_server_key(prep);
>  }
>
> @@ -99,7 +102,7 @@ static void rxrpc_destroy_s(struct key *key)
>  {
>         const struct rxrpc_security *sec = key->payload.data[1];
>
> -       if (sec)
> +       if (sec && sec->destroy_server_key)
>                 sec->destroy_server_key(key);
>  }
>
>
> base-commit: b47d5a4f6b8d42f8a8fbe891b36215e4fddc53be
> --
> 2.25.1

Actually ran into this while experimenting; looks fine and fixes the problem.

Acked-by: Marc Dionne <marc.dionne at auristor.com>

Marc