linux-kernel - Re: [PATCH] nfsd: Fix a memory leak in an error handling path

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Date:   Tue, 30 Aug 2022 21:11:54 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
CC:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Jeff Layton <jlayton@...nel.org>,
        Bruce Fields <bfields@...hat.com>,
        Scott Mayhew <smayhew@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH] nfsd: Fix a memory leak in an error handling path



> On Aug 26, 2022, at 7:08 AM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
> 
> On Fri, Aug 26, 2022 at 12:24:54PM +0200, Christophe JAILLET wrote:
>> If this memdup_user() call fails, the memory allocated in a previous call
>> a few lines above should be freed. Otherwise it leaks.
>> 
>> Fixes: 6ee95d1c8991 ("nfsd: add support for upcall version 2")
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
>> ---
>> Speculative, untested.
>> ---
>> fs/nfsd/nfs4recover.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>> 
>> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
>> index b29d27eaa8a6..248ff9f4141c 100644
>> --- a/fs/nfsd/nfs4recover.c
>> +++ b/fs/nfsd/nfs4recover.c
>> @@ -815,8 +815,10 @@ __cld_pipe_inprogress_downcall(const struct cld_msg_v2 __user *cmsg,
>> 				princhash.data = memdup_user(
>> 						&ci->cc_princhash.cp_data,
>> 						princhashlen);
>> -				if (IS_ERR_OR_NULL(princhash.data))
>> +				if (IS_ERR_OR_NULL(princhash.data)) {
>> +					kfree(name.data);
>> 					return -EFAULT;
> 
> This comment is not directed at you and is not related to your patch.
> But memdup_user() never returns NULL, only error pointers.  I wrote a
> fifteen page blog entry about NULL vs error pointers the other week.
> https://staticthinking.wordpress.com/2022/08/01/mixing-error-pointers-and-null/
> This should propagate the error code from memdup_user() instead of
> -EFAULT.

I take it then that Christophe should redrive this with your suggested
corrections? I haven't applied this yet because I was waiting for
follow-up.


--
Chuck Lever