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

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Message-Id: <2C44474C-1803-4B94-8140-6DF64A87418F@netapp.com>
Date:	Tue, 18 Jan 2011 09:43:22 -0500
From:	Andy Adamson <andros@...app.com>
To:	Jesper Juhl <jj@...osbits.net>
Cc:	Mi Jinlong <mijinlong@...fujitsu.com>, linux-nfs@...r.kernel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-kernel@...r.kernel.org, Fred Isaman <iisaman@...app.com>
Subject: Re: [PATCH] NFS4: Avoid potential NULL pointer dereference in decode_and_add_ds().


On Jan 17, 2011, at 1:41 PM, Jesper Juhl wrote:

> On Mon, 17 Jan 2011, Mi Jinlong wrote:
> 
>> 
>> 
>> 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().



Yes - good catch.

-->Andy

>>> 
>>> 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);
>> 
> Missed that one. Thanks. 
> 
> Signed-off-by: Jesper Juhl <jj@...osbits.net>
> ---
> nfs4filelayoutdev.c |    9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/nfs4filelayoutdev.c b/fs/nfs/nfs4filelayoutdev.c
> index 51fe64a..f5c9b12 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 = '-';
> 	}
> 
> @@ -240,7 +245,7 @@ decode_and_add_ds(__be32 **pp, struct inode *inode)
> 	port = htons((tmp[0] << 8) | (tmp[1]));
> 
> 	ds = nfs4_pnfs_ds_add(inode, ip_addr, port);
> -	dprintk("%s Decoded address and port %s\n", __func__, buf);
> +	dprintk("%s: Decoded address and port %s\n", __func__, buf);
> out_free:
> 	kfree(buf);
> out_err:
> 
> 
> -- 
> Jesper Juhl <jj@...osbits.net>            http://www.chaosbits.net/
> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
> Plain text mails only, please.
> 
> --
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