Re: [PATCH 1/1] net: Fix use of proc_fs

On Sat, Dec 12, 2020 at 11:51 PM Jakub Kicinski [off-list ref] wrote:

On Sat, 12 Dec 2020 23:39:20 +0200 Yonatan Linik wrote:

quoted

On Sat, Dec 12, 2020 at 9:48 PM Jakub Kicinski [off-list ref] wrote:

quoted

On Fri, 11 Dec 2020 18:37:49 +0200 Yonatan Linik wrote:

quoted

proc_fs was used, in af_packet, without a surrounding #ifdef,
although there is no hard dependency on proc_fs.
That caused the initialization of the af_packet module to fail
when CONFIG_PROC_FS=n.

Specifically, proc_create_net() was used in af_packet.c,
and when it fails, packet_net_init() returns -ENOMEM.
It will always fail when the kernel is compiled without proc_fs,
because, proc_create_net() for example always returns NULL.

The calling order that starts in af_packet.c is as follows:
packet_init()
register_pernet_subsys()
register_pernet_operations()
__register_pernet_operations()
ops_init()
ops->init() (packet_net_ops.init=packet_net_init())
proc_create_net()

It worked in the past because register_pernet_subsys()'s return value
wasn't checked before this Commit 36096f2f4fa0 ("packet: Fix error path in
packet_init.").
It always returned an error, but was not checked before, so everything
was working even when CONFIG_PROC_FS=n.

The fix here is simply to add the necessary #ifdef.

Signed-off-by: Yonatan Linik <redacted>

Hm, I'm guessing you hit this on a kernel upgrade of a real system?

Yeah, suddenly using socket with AF_PACKET didn't work,
so I checked what happened.

quoted

It seems like all callers to proc_create_net (and friends) interpret
NULL as an error, but only handful is protected by an ifdef.

I guess where there is no ifdef,
there should be a hard dependency on procfs,
using depends on in the Kconfig.
Maybe that's not the case everywhere it should be.

You're right, on a closer look most of the places have a larger #ifdef
block (which my grep didn't catch) or are under Kconfig. Of those I
checked only TLS looks wrong (good job me) - would you care to fix that
one as well, or should I?

I can fix that as well, you are talking about tls_proc.c, right?