Re: [PATCH 1/1] gtp: fix use-after-free and null-ptr-deref in gtp_genl_dump_pdp()

[Eric Dumazet]

On Wed, Jan 24, 2024 at 11:14 AM <kovalev@xxxxxxxxxxxx> wrote:
>
> From: Vasiliy Kovalev <kovalev@xxxxxxxxxxxx>
>
> After unloading the module, an instance continues to exist that accesses
> outdated memory addresses.
>
> To prevent this, the dump_pdp_en flag has been added, which blocks the
> dump of pdp contexts by a false value. And only after these checks can
> the net_generic() function be called.
>
> These errors were found using the syzkaller program:
>
> Syzkaller hit 'general protection fault in gtp_genl_dump_pdp' bug.
> gtp: GTP module loaded (pdp ctx size 104 bytes)
> gtp: GTP module unloaded
> general protection fault, probably for non-canonical address
> 0xdffffc0000000001:0000 [#1] SMP KASAN NOPTI
> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> CPU: 0 PID: 2782 Comm: syz-executor139 Not tainted 5.10.200-std-def-alt1 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-alt1
> RIP: 0010:gtp_genl_dump_pdp+0x1b1/0x790 [gtp]
> ...
> Call Trace:
>  genl_lock_dumpit+0x6b/0xa0 net/netlink/genetlink.c:623
>  netlink_dump+0x575/0xc70 net/netlink/af_netlink.c:2271
>  __netlink_dump_start+0x64e/0x910 net/netlink/af_netlink.c:2376
>  genl_family_rcv_msg_dumpit+0x2b8/0x310 net/netlink/genetlink.c:686
>  genl_family_rcv_msg net/netlink/genetlink.c:780 [inline]
>  genl_rcv_msg+0x450/0x5a0 net/netlink/genetlink.c:800
>  netlink_rcv_skb+0x150/0x440 net/netlink/af_netlink.c:2497
>  genl_rcv+0x29/0x40 net/netlink/genetlink.c:811
>  netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
>  netlink_unicast+0x54e/0x800 net/netlink/af_netlink.c:1348
>  netlink_sendmsg+0x914/0xe00 net/netlink/af_netlink.c:1916
>  sock_sendmsg_nosec net/socket.c:651 [inline]
>  __sock_sendmsg+0x159/0x190 net/socket.c:663
>  ____sys_sendmsg+0x712/0x870 net/socket.c:2376
>  ___sys_sendmsg+0xf8/0x170 net/socket.c:2430
>  __sys_sendmsg+0xea/0x1b0 net/socket.c:2459
>  do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x62/0xc7
> RIP: 0033:0x7f2ea16c2d49
>
> Fixes: 94a6d9fb88df ("gtp: fix wrong condition in gtp_genl_dump_pdp()")
> Signed-off-by: Vasiliy Kovalev <kovalev@xxxxxxxxxxxx>
> ---
>  drivers/net/gtp.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
> index 477b4d4f860bd3..3fc4639711cd83 100644
> --- a/drivers/net/gtp.c
> +++ b/drivers/net/gtp.c
> @@ -1675,6 +1675,8 @@ static int gtp_genl_get_pdp(struct sk_buff *skb, struct genl_info *info)
>         return err;
>  }
>
> +static bool dump_pdp_en;
> +

Hmm, it seems there is a missing try_module_get() somewhere...

__netlink_dump_start() does one, so perhaps we reach __netlink_dump_start()
with a NULL in control->module ?