Re: [PATCH] smb/client: avoid possible NULL dereference in cifs_free_subrequest()

[Steve French]

Updated patch to change Fixes tag and Cc: David


On Fri, Aug 9, 2024 at 10:42 AM Steve French <smfrench@xxxxxxxxx> wrote:
>
> On Fri, Aug 9, 2024 at 10:11 AM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> >
> > On Fri, Aug 09, 2024 at 06:00:26PM +0300, Dan Carpenter wrote:
> > > On Thu, Aug 08, 2024 at 08:23:32PM +0800, Su Hui wrote:
> > > > Clang static checker (scan-build) warning:
> > > >     cifsglob.h:line 890, column 3
> > > >     Access to field 'ops' results in a dereference of a null pointer.
> > > >
> > > > Commit 519be989717c ("cifs: Add a tracepoint to track credits involved in
> > > > R/W requests") adds a check for 'rdata->server', and let clang throw this
> > > > warning about NULL dereference.
> > > >
> > > > When 'rdata->credits.value != 0 && rdata->server == NULL' happens,
> > > > add_credits_and_wake_if() will call rdata->server->ops->add_credits().
> > > > This will cause NULL dereference problem. Add a check for 'rdata->server'
> > > > to avoid NULL dereference.
> > > >
> > > > Signed-off-by: Su Hui <suhui@xxxxxxxxxxxx>
> > >
> > > Needs a Fixes tag.
> > >
> > > Also when you add a Fixes tag, then get_maintainer will add the David Howells
> > > automatically.  I've added him manually.
> > >
> >
> > Actually, David should have been CC'd but the fixes tag wouldn't have pointed
> > to his patch.
> >
> > This is an inconsistent NULL checking warning.  It's not clear to me if the NULL
> > checks should be removed or more added.  If David were trying to fix a NULL
> > pointer dereference and accidentally left one unchecked dereference out then the
> > Fixes tag would point to his patch.  Since David was doing something unrelated
>
> Looks like (if this is even possible for server to to be null) then I
> will need to change
> the fixes to commit 69c3c023af25. I will update the tag in the current
> patch in for-next
>
> Author: David Howells <dhowells@xxxxxxxxxx>
> Date:   Fri Oct 6 18:16:15 2023 +0100
>
>     cifs: Implement netfslib hooks
>
>     Provide implementation of the netfslib hooks that will be used by netfslib
>     to ask cifs to set up and perform operations.
> --
> Thanks,
>
> Steve



-- 
Thanks,

Steve
From 59ac1aac1550731ca241007af660fc5278c88136 Mon Sep 17 00:00:00 2001
From: Su Hui <suhui@xxxxxxxxxxxx>
Date: Thu, 8 Aug 2024 20:23:32 +0800
Subject: [PATCH] smb/client: avoid possible NULL dereference in
 cifs_free_subrequest()

Clang static checker (scan-build) warning:
	cifsglob.h:line 890, column 3
	Access to field 'ops' results in a dereference of a null pointer.

Commit 519be989717c ("cifs: Add a tracepoint to track credits involved in
R/W requests") adds a check for 'rdata->server', and let clang throw this
warning about NULL dereference.

When 'rdata->credits.value != 0 && rdata->server == NULL' happens,
add_credits_and_wake_if() will call rdata->server->ops->add_credits().
This will cause NULL dereference problem. Add a check for 'rdata->server'
to avoid NULL dereference.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 69c3c023af25 ("cifs: Implement netfslib hooks")
Cc: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Su Hui <suhui@xxxxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
---
 fs/smb/client/file.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index b2405dd4d4d4..45459af5044d 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -315,7 +315,7 @@ static void cifs_free_subrequest(struct netfs_io_subrequest *subreq)
 #endif
 	}
 
-	if (rdata->credits.value != 0)
+	if (rdata->credits.value != 0) {
 		trace_smb3_rw_credits(rdata->rreq->debug_id,
 				      rdata->subreq.debug_index,
 				      rdata->credits.value,
@@ -323,8 +323,12 @@ static void cifs_free_subrequest(struct netfs_io_subrequest *subreq)
 				      rdata->server ? rdata->server->in_flight : 0,
 				      -rdata->credits.value,
 				      cifs_trace_rw_credits_free_subreq);
+		if (rdata->server)
+			add_credits_and_wake_if(rdata->server, &rdata->credits, 0);
+		else
+			rdata->credits.value = 0;
+	}
 
-	add_credits_and_wake_if(rdata->server, &rdata->credits, 0);
 	if (rdata->have_xid)
 		free_xid(rdata->xid);
 }
-- 
2.43.0