linux-kernel - Re: [PATCH] NFS4: Avoid potential NULL pointer dereference in decode_and_add

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Message-ID: <4D33B30A.8050507@cn.fujitsu.com>
Date:	Mon, 17 Jan 2011 11:10:02 +0800
From:	Mi Jinlong <mijinlong@...fujitsu.com>
To:	Jesper Juhl <jj@...osbits.net>
CC:	linux-nfs@...r.kernel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NFS4: Avoid potential NULL pointer dereference in decode_and_add_ds().



Jesper Juhl:
> strrchr() can return NULL if nothing is found. If this happens we'll 
> dereference a NULL pointer in 
> fs/nfs/nfs4filelayoutdev.c::decode_and_add_ds().
> 
> I tried to find some other code that guarantees that this can never 
> happen but I was unsuccessful. So, unless someone else can point to some 
> code that ensures this can never be a problem, I believe this patch is 
> needed.
> 
> While I was changing this code I also noticed that all the dprintk() 
> statements, except one, start with "%s:". The one missing the ":" I added 
> it to.

  Maybe another one also should be changed at decode_and_add_ds() at line 243:

   243  printk("%s Decoded address and port %s\n", __func__, buf);

-- 
----
thanks
Mi Jinlong

> 
> Signed-off-by: Jesper Juhl <jj@...osbits.net>
> ---
>  nfs4filelayoutdev.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
>   only compile tested.
> 
> diff --git a/fs/nfs/nfs4filelayoutdev.c b/fs/nfs/nfs4filelayoutdev.c
> index 51fe64a..5a85b8f 100644
> --- a/fs/nfs/nfs4filelayoutdev.c
> +++ b/fs/nfs/nfs4filelayoutdev.c
> @@ -214,7 +214,7 @@ decode_and_add_ds(__be32 **pp, struct inode *inode)
>  
>  	/* ipv6 length plus port is legal */
>  	if (rlen > INET6_ADDRSTRLEN + 8) {
> -		dprintk("%s Invalid address, length %d\n", __func__,
> +		dprintk("%s: Invalid address, length %d\n", __func__,
>  			rlen);
>  		goto out_err;
>  	}
> @@ -225,6 +225,11 @@ decode_and_add_ds(__be32 **pp, struct inode *inode)
>  	/* replace the port dots with dashes for the in4_pton() delimiter*/
>  	for (i = 0; i < 2; i++) {
>  		char *res = strrchr(buf, '.');
> +		if (!res) {
> +			dprintk("%s: Failed finding expected dots in port\n",
> +				__func__);
> +			goto out_free;
> +		}
>  		*res = '-';
>  	}
>  
> 

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