linux-kernel - Re: [PATCH next] smb: client: Fix use after free in send

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Message-ID: <e291d925-bfd9-4202-b5d4-de5bf30ab870@samba.org>
Date: Wed, 6 Aug 2025 16:17:41 +0200
From: Stefan Metzmacher <metze@...ba.org>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Steve French <sfrench@...ba.org>, Paulo Alcantara <pc@...guebit.org>,
 Ronnie Sahlberg <ronniesahlberg@...il.com>,
 Shyam Prasad N <sprasad@...rosoft.com>, Tom Talpey <tom@...pey.com>,
 Bharath SM <bharathsm@...rosoft.com>, linux-cifs@...r.kernel.org,
 samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org,
 kernel-janitors@...r.kernel.org
Subject: Re: [PATCH next] smb: client: Fix use after free in send_done()

Am 06.08.25 um 14:48 schrieb Dan Carpenter:
> On Wed, Aug 06, 2025 at 02:20:56PM +0200, Stefan Metzmacher wrote:
>> Hi Dan,
>>
>>> The mempool_free() function frees "request".  Don't free the request
>>> until after smbd_disconnect_rdma_connection() to avoid a use after free
>>> bug.
>>>
>>> Fixes: 5e65668c75c0 ("smb: client: let send_done() cleanup before calling smbd_disconnect_rdma_connection()")
>>> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
>>> ---
>>>    fs/smb/client/smbdirect.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
>>> index 58321e483a1a..162f8d1c548a 100644
>>> --- a/fs/smb/client/smbdirect.c
>>> +++ b/fs/smb/client/smbdirect.c
>>> @@ -286,8 +286,8 @@ static void send_done(struct ib_cq *cq, struct ib_wc *wc)
>>>    	if (wc->status != IB_WC_SUCCESS || wc->opcode != IB_WC_SEND) {
>>>    		log_rdma_send(ERR, "wc->status=%d wc->opcode=%d\n",
>>>    			wc->status, wc->opcode);
>>> -		mempool_free(request, request->info->request_mempool);
>>>    		smbd_disconnect_rdma_connection(request->info);
>>> +		mempool_free(request, request->info->request_mempool);
>>
>> The correct fix is to use 'info' instead of 'request->info'
>> other than that the order needs to stay that way.
>>
>> I already asked Steve to squash such a change into the
>> original commit (which is not yet upstream).
>>
>> See:
>> https://lore.kernel.org/linux-cifs/cover.1754308712.git.metze@samba.org/T/#m98a8607d7b83a11fd78547306836a872a2a27192
>>
>> What was the test that triggered the problem?
>> Or did you only noticed it by looking at the code?
> 
> This was a Smatch static checker warning.  You need to have the cross
> function DB to detect it.

Ok, I'll try to integrate it into my build flow...

Does it replace sparse or does it run in addition?
If it replaces sparse I guess a small script would
run them both?

$ cat mychecker.sh:
#!/bin/bash
set -e
sparse $@
smatch $@

And maybe all others from
https://gautammenghani.com/linux,/c/2022/05/19/static-analysis-tools-linux-kernel.html

How often do I need to run smatch_scripts/build_kernel_data.sh on the whole kernel?

Thanks!
metze