linux-kernel - Re: [PATCH next] smb: client: Fix NULL vs ERR_PTR() returns in cifs_get_tcon

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Message-ID: <89a2023c-e383-4780-83e3-ba8f9e44c015@huaweicloud.com>
Date: Mon, 18 Aug 2025 21:03:44 +0800
From: Wang Zhaolong <wangzhaolong@...weicloud.com>
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 NULL vs ERR_PTR() returns in
 cifs_get_tcon_super()



> The cifs_get_tcon_super() function returns NULL on error but the caller
> expect it to return error pointers instead.  Change it to return error
> pointers.  Otherwise it results in a NULL pointer dereference.
> 
> Fixes: 0938b093b1ae ("smb: client: Fix mount deadlock by avoiding super block iteration in DFS reconnect")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>

Hi Dan,

Thank you for your patch and for taking the time to address this issue.

I would like to mention that I have recently sent out the V4 version of
the patch series, which addresses the issues related to `cifs_get_tcon_super()`.
In the latest version, the issue of NULL pointer dereference has already
been resolved.

https://lore.kernel.org/all/CAH2r5msLMNdqdo6EBuTvrQ0hwrqSRC-LSZuN2WpwV+PkDwsCOw@mail.gmail.com/

I avoid null pointer dereferencing by performing a null pointer check on
the return value of cifs_get_dfs_tcon_super().


> ---
>   fs/smb/client/misc.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/smb/client/misc.c b/fs/smb/client/misc.c
> index 3b6920a52daa..d73c36862e97 100644
> --- a/fs/smb/client/misc.c
> +++ b/fs/smb/client/misc.c
> @@ -1116,7 +1116,7 @@ static struct super_block *cifs_get_tcon_super(struct cifs_tcon *tcon)
>   	struct cifs_sb_info *cifs_sb;
>   
>   	if (!tcon)
> -		return NULL;
> +		return ERR_PTR(-EINVAL);
>   
>   	spin_lock(&tcon->sb_list_lock);
>   	list_for_each_entry(cifs_sb, &tcon->cifs_sb_list, tcon_sb_link) {
> @@ -1141,7 +1141,7 @@ static struct super_block *cifs_get_tcon_super(struct cifs_tcon *tcon)
>   	}
>   	spin_unlock(&tcon->sb_list_lock);
>   
> -	return NULL;
> +	return ERR_PTR(-ENOENT);
>   }
>   
>   struct super_block *cifs_get_dfs_tcon_super(struct cifs_tcon *tcon)

Additionally, I think it somewhat peculiar that in the current
implementation, cifs_get_tcon_super() returns -EINVAL.

I would greatly appreciate it if you could review my latest patch series to
confirm if it resolves the concerns. If there are any additional improvements, I
would be happy to collaborate further to ensure the best possible solution.

Best regards,
Wang Zhaolong