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Message-id: <172730054387.17050.12447592116066223771@noble.neil.brown.name>
Date: Thu, 26 Sep 2024 07:42:23 +1000
From: "NeilBrown" <neilb@...e.de>
To: "Mirsad Todorovac" <mtodorovac69@...il.com>
Cc: linux-nfs@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, "Chuck Lever" <chuck.lever@...cle.com>,
"Jeff Layton" <jlayton@...nel.org>, "Olga Kornievskaia" <okorniev@...hat.com>,
"Dai Ngo" <Dai.Ngo@...cle.com>, "Tom Talpey" <tom@...pey.com>,
"Trond Myklebust" <trondmy@...nel.org>, "Anna Schumaker" <anna@...nel.org>,
"David S. Miller" <davem@...emloft.net>, "Eric Dumazet" <edumazet@...gle.com>,
"Jakub Kicinski" <kuba@...nel.org>, "Paolo Abeni" <pabeni@...hat.com>
Subject: Re: [PATCH v1 1/1] SUNRPC: Make enough room in servername[] for
AF_UNIX addresses
On Thu, 26 Sep 2024, Mirsad Todorovac wrote:
> On 9/24/24 12:43, NeilBrown wrote:
> > On Tue, 24 Sep 2024, Mirsad Todorovac wrote:
> >> Hi, Neil,
> >>
> >> Apparently I was duplicating work.
> >>
> >> However, using
> >>
> >> char servername[UNIX_PATH_MAX];
> >>
> >> has some advantages when compared to hard-coded integer?
> >>
> >> Correct me if I'm wrong.
> >
> > I think you are wrong. I agree that 48 is a poor choice. I think that
> > UNIX_PATH_MAX is a poor choice too. The "servername" string is used for
> > things other than a UNIX socket path.
> > Did you read all of the thread that I provided a link for? I suggest a
> > more meaningful number in one of the later messages.
>
> I see. Thanks for the tip. However, if UNIX_PATH_MAX ever changes in the
> future, the decl
>
> char servername[108];
>
> might be missed when fixing all the changes caused by the change of the
> macro definition? Am I wrong again?
Realistically UNIX_PATH_MAX is never going to change, and if it did that
would not affect the correctness of this code.
>
> Making it logically depend on the system limits might save some headache
> in the future, perhaps.
Unlikely. Did you look to see what the failure mode is here?
servername is only ever used in log messages. Truncating names in log
message at 8 bytes can certainly be annoying. Truncating at 48 bytes is
much less of a problem.
>
> If really the biggest string that will be copied there is: "/var/run/rpcbind.sock",
> you are then right - stack space is precious commodity, and allocating
> via kmalloc() might preempt the caller thread.
It might. But the string is always passed to xprt_create_transport()
which always calls kstrdup() on it. So maybe that doesn't matter. (As
I said, understanding the big picture is important).
>
> However, you got to this five weeks earlier - but the patch did not
> propagate to the main vanilla torvalds tree.
Actually it has.
Commit 9090a7f78623 ("SUNRPC: Fix -Wformat-truncation warning")
$ git show --format=fuller 9090a7f78623 | grep CommitDate
CommitDate: Mon Sep 23 15:03:13 2024 -0400
Linus merged it
Commit 684a64bf32b6 ("Merge tag 'nfs-for-6.12-1' of git://git.linux-nfs.org/projects/anna/linux-nfs")
Date: Tue Sep 24 15:44:18 2024 -0700
That patch used RPC_MAXNETNAMELEN which is the least-ugly simple fix.
Thanks for your interest in improving Linux.
NeilBrown
>
> Best regards,
> Mirsad Todorovac
>
> > But I really think that the problem here is the warning. The servername
> > array is ALWAYS big enough for any string that will actually be copied
> > into it. gcc isn't clever enough to detect that, but it tries to be
> > clever enough to tell you that even though you used snprintf so you know
> > that the string might in theory overflow, it decides to warn you about
> > something you already know.
> >
> > i.e. if you want to fix this, I would rather you complain the the
> > compiler writers. Or maybe suggest a #pragma to silence the warning in
> > this case. Or maybe examine all of the code instead of the one line
> > that triggers the warning and see if there is a better approach to
> > providing the functionality that is being provided here.
> >
> > NeilBrown
> >
> >>
> >> Best regards,
> >> Mirsad Todorovac
> >>
> >> On 9/23/24 23:24, NeilBrown wrote:
> >>> On Tue, 24 Sep 2024, Mirsad Todorovac wrote:
> >>>> GCC 13.2.0 reported with W=1 build option the following warning:
> >>>
> >>> See
> >>> https://lore.kernel.org/all/20240814093853.48657-1-kunwu.chan@linux.dev/
> >>>
> >>> I don't think anyone really cares about this one.
> >>>
> >>> NeilBrown
> >>>
> >>>
> >>>>
> >>>> net/sunrpc/clnt.c: In function ‘rpc_create’:
> >>>> net/sunrpc/clnt.c:582:75: warning: ‘%s’ directive output may be truncated writing up to 107 bytes into \
> >>>> a region of size 48 [-Wformat-truncation=]
> >>>> 582 | snprintf(servername, sizeof(servername), "%s",
> >>>> | ^~
> >>>> net/sunrpc/clnt.c:582:33: note: ‘snprintf’ output between 1 and 108 bytes into a destination of size 48
> >>>> 582 | snprintf(servername, sizeof(servername), "%s",
> >>>> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>>> 583 | sun->sun_path);
> >>>> | ~~~~~~~~~~~~~~
> >>>>
> >>>> 548 };
> >>>> → 549 char servername[48];
> >>>> 550 struct rpc_clnt *clnt;
> >>>> 551 int i;
> >>>> 552
> >>>> 553 if (args->bc_xprt) {
> >>>> 554 WARN_ON_ONCE(!(args->protocol & XPRT_TRANSPORT_BC));
> >>>> 555 xprt = args->bc_xprt->xpt_bc_xprt;
> >>>> 556 if (xprt) {
> >>>> 557 xprt_get(xprt);
> >>>> 558 return rpc_create_xprt(args, xprt);
> >>>> 559 }
> >>>> 560 }
> >>>> 561
> >>>> 562 if (args->flags & RPC_CLNT_CREATE_INFINITE_SLOTS)
> >>>> 563 xprtargs.flags |= XPRT_CREATE_INFINITE_SLOTS;
> >>>> 564 if (args->flags & RPC_CLNT_CREATE_NO_IDLE_TIMEOUT)
> >>>> 565 xprtargs.flags |= XPRT_CREATE_NO_IDLE_TIMEOUT;
> >>>> 566 /*
> >>>> 567 * If the caller chooses not to specify a hostname, whip
> >>>> 568 * up a string representation of the passed-in address.
> >>>> 569 */
> >>>> 570 if (xprtargs.servername == NULL) {
> >>>> 571 struct sockaddr_un *sun =
> >>>> 572 (struct sockaddr_un *)args->address;
> >>>> 573 struct sockaddr_in *sin =
> >>>> 574 (struct sockaddr_in *)args->address;
> >>>> 575 struct sockaddr_in6 *sin6 =
> >>>> 576 (struct sockaddr_in6 *)args->address;
> >>>> 577
> >>>> 578 servername[0] = '\0';
> >>>> 579 switch (args->address->sa_family) {
> >>>> → 580 case AF_LOCAL:
> >>>> → 581 if (sun->sun_path[0])
> >>>> → 582 snprintf(servername, sizeof(servername), "%s",
> >>>> → 583 sun->sun_path);
> >>>> → 584 else
> >>>> → 585 snprintf(servername, sizeof(servername), "@%s",
> >>>> → 586 sun->sun_path+1);
> >>>> → 587 break;
> >>>> 588 case AF_INET:
> >>>> 589 snprintf(servername, sizeof(servername), "%pI4",
> >>>> 590 &sin->sin_addr.s_addr);
> >>>> 591 break;
> >>>> 592 case AF_INET6:
> >>>> 593 snprintf(servername, sizeof(servername), "%pI6",
> >>>> 594 &sin6->sin6_addr);
> >>>> 595 break;
> >>>> 596 default:
> >>>> 597 /* caller wants default server name, but
> >>>> 598 * address family isn't recognized. */
> >>>> 599 return ERR_PTR(-EINVAL);
> >>>> 600 }
> >>>> 601 xprtargs.servername = servername;
> >>>> 602 }
> >>>> 603
> >>>> 604 xprt = xprt_create_transport(&xprtargs);
> >>>> 605 if (IS_ERR(xprt))
> >>>> 606 return (struct rpc_clnt *)xprt;
> >>>>
> >>>> After the address family AF_LOCAL was added in the commit 176e21ee2ec89, the old hard-coded
> >>>> size for servername of char servername[48] no longer fits. The maximum AF_UNIX address size
> >>>> has now grown to UNIX_PATH_MAX defined as 108 in "include/uapi/linux/un.h" .
> >>>>
> >>>> The lines 580-587 were added later, addressing the leading zero byte '\0', but did not fix
> >>>> the hard-coded servername limit.
> >>>>
> >>>> The AF_UNIX address was truncated to 47 bytes + terminating null byte. This patch will fix the
> >>>> servername in AF_UNIX family to the maximum permitted by the system:
> >>>>
> >>>> 548 };
> >>>> → 549 char servername[UNIX_PATH_MAX];
> >>>> 550 struct rpc_clnt *clnt;
> >>>>
> >>>> Fixes: 4388ce05fa38b ("SUNRPC: support abstract unix socket addresses")
> >>>> Fixes: 510deb0d7035d ("SUNRPC: rpc_create() default hostname should support AF_INET6 addresses")
> >>>> Fixes: 176e21ee2ec89 ("SUNRPC: Support for RPC over AF_LOCAL transports")
> >>>> Cc: Neil Brown <neilb@...e.de>
> >>>> Cc: Chuck Lever <chuck.lever@...cle.com>
> >>>> Cc: Trond Myklebust <trondmy@...nel.org>
> >>>> Cc: Anna Schumaker <anna@...nel.org>
> >>>> Cc: Jeff Layton <jlayton@...nel.org>
> >>>> Cc: Olga Kornievskaia <okorniev@...hat.com>
> >>>> Cc: Dai Ngo <Dai.Ngo@...cle.com>
> >>>> Cc: Tom Talpey <tom@...pey.com>
> >>>> Cc: "David S. Miller" <davem@...emloft.net>
> >>>> Cc: Eric Dumazet <edumazet@...gle.com>
> >>>> Cc: Jakub Kicinski <kuba@...nel.org>
> >>>> Cc: Paolo Abeni <pabeni@...hat.com>
> >>>> Cc: linux-nfs@...r.kernel.org
> >>>> Cc: netdev@...r.kernel.org
> >>>> Cc: linux-kernel@...r.kernel.org
> >>>> Signed-off-by: Mirsad Todorovac <mtodorovac69@...il.com>
> >>>> ---
> >>>> v1:
> >>>> initial version.
> >>>>
> >>>> net/sunrpc/clnt.c | 2 +-
> >>>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> >>>> index 09f29a95f2bc..67099719893e 100644
> >>>> --- a/net/sunrpc/clnt.c
> >>>> +++ b/net/sunrpc/clnt.c
> >>>> @@ -546,7 +546,7 @@ struct rpc_clnt *rpc_create(struct rpc_create_args *args)
> >>>> .connect_timeout = args->connect_timeout,
> >>>> .reconnect_timeout = args->reconnect_timeout,
> >>>> };
> >>>> - char servername[48];
> >>>> + char servername[UNIX_PATH_MAX];
> >>>> struct rpc_clnt *clnt;
> >>>> int i;
> >>>>
> >>>> --
> >>>> 2.43.0
> >>>>
> >>>>
> >>>
> >>
> >
>
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