[PATCH] net: 9p: fix possible memory leak in p9_check_errors()

[PATCH] net: 9p: fix possible memory leak in p9_check_errors()

[Hangyu Hua]

When p9pdu_readf is called with "s?d" attribute, it allocates a pointer
that will store a string. But when p9pdu_readf() fails while handling "d"
then this pointer will not be freed in p9_check_errors.

Fixes: ca41bb3e21d7 ("[net/9p] Handle Zero Copy TREAD/RERROR case in !dotl case.")
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
---
 net/9p/client.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index 86bbc7147fc1..6c7cd765b714 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -540,12 +540,15 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
 		return 0;
 
 	if (!p9_is_proto_dotl(c)) {
-		char *ename;
+		char *ename = NULL;
 
 		err = p9pdu_readf(&req->rc, c->proto_version, "s?d",
 				  &ename, &ecode);
-		if (err)
+		if (err) {
+			if (ename != NULL)
+				kfree(ename);
 			goto out_err;
+		}
 
 		if (p9_is_proto_dotu(c) && ecode < 512)
 			err = -ecode;
-- 
2.34.1

Re: [PATCH] net: 9p: fix possible memory leak in p9_check_errors()

[asmadeus]

Hangyu Hua wrote on Thu, Oct 26, 2023 at 05:23:51PM +0800:
> When p9pdu_readf is called with "s?d" attribute, it allocates a pointer
> that will store a string. But when p9pdu_readf() fails while handling "d"
> then this pointer will not be freed in p9_check_errors.

Right, that sounds correct to me.

Out of curiosity how did you notice this? The leak shouldn't happen with
any valid server.

This cannot break anything so I'll push this to -next tomorrow and
submit to Linus next week

> Fixes: ca41bb3e21d7 ("[net/9p] Handle Zero Copy TREAD/RERROR case in !dotl case.")

This commit moves this code a bit, but the p9pdu_readf call predates
it -- in this case the Fixes tag is probably not useful; this affects
all maintained kernels.

> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
> ---
>  net/9p/client.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 86bbc7147fc1..6c7cd765b714 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -540,12 +540,15 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
>  		return 0;
>  
>  	if (!p9_is_proto_dotl(c)) {
> -		char *ename;
> +		char *ename = NULL;
>  
>  		err = p9pdu_readf(&req->rc, c->proto_version, "s?d",
>  				  &ename, &ecode);
> -		if (err)
> +		if (err) {
> +			if (ename != NULL)
> +				kfree(ename);

Don't check for NULL before kfree - kfree does it.
If that's the only remark you get I can fix it when applying the commit
on my side.


>  			goto out_err;
> +		}
>  
>  		if (p9_is_proto_dotu(c) && ecode < 512)
>  			err = -ecode;

-- 
Dominique Martinet | Asmadeus

Re: [PATCH] net: 9p: fix possible memory leak in p9_check_errors()

[Christian Schoenebeck]

On Thursday, October 26, 2023 1:53:55 PM CEST asmadeus@codewreck.org wrote:
> 
> Hangyu Hua wrote on Thu, Oct 26, 2023 at 05:23:51PM +0800:
> > When p9pdu_readf is called with "s?d" attribute, it allocates a pointer
> > that will store a string. But when p9pdu_readf() fails while handling "d"
> > then this pointer will not be freed in p9_check_errors.
> 
> Right, that sounds correct to me.
> 
> Out of curiosity how did you notice this? The leak shouldn't happen with
> any valid server.
> 
> This cannot break anything so I'll push this to -next tomorrow and
> submit to Linus next week
> 
> > Fixes: ca41bb3e21d7 ("[net/9p] Handle Zero Copy TREAD/RERROR case in !dotl case.")
> 
> This commit moves this code a bit, but the p9pdu_readf call predates
> it -- in this case the Fixes tag is probably not useful; this affects
> all maintained kernels.

Looks like it exists since introduction of p9_check_errors(), therefore:

Fixes: 51a87c552dfd ("9p: rework client code to use new protocol support functions")

> > Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
> > ---
> >  net/9p/client.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/9p/client.c b/net/9p/client.c
> > index 86bbc7147fc1..6c7cd765b714 100644
> > --- a/net/9p/client.c
> > +++ b/net/9p/client.c
> > @@ -540,12 +540,15 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
> >  		return 0;
> >  
> >  	if (!p9_is_proto_dotl(c)) {
> > -		char *ename;
> > +		char *ename = NULL;
> >  
> >  		err = p9pdu_readf(&req->rc, c->proto_version, "s?d",
> >  				  &ename, &ecode);
> > -		if (err)
> > +		if (err) {
> > +			if (ename != NULL)
> > +				kfree(ename);
> 
> Don't check for NULL before kfree - kfree does it.
> If that's the only remark you get I can fix it when applying the commit
> on my side.

With those two remarks addressed:

Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>

> 
> 
> >  			goto out_err;
> > +		}
> >  
> >  		if (p9_is_proto_dotu(c) && ecode < 512)
> >  			err = -ecode;
> 
> 

Re: [PATCH] net: 9p: fix possible memory leak in p9_check_errors()

[Hangyu Hua]

On 26/10/2023 19:53, asmadeus@codewreck.org wrote:
> 
> Hangyu Hua wrote on Thu, Oct 26, 2023 at 05:23:51PM +0800:
>> When p9pdu_readf is called with "s?d" attribute, it allocates a pointer
>> that will store a string. But when p9pdu_readf() fails while handling "d"
>> then this pointer will not be freed in p9_check_errors.
> 
> Right, that sounds correct to me.
> 
> Out of curiosity how did you notice this? The leak shouldn't happen with
> any valid server.

I just found that any attributes that require memory allocation are 
prone to errors when mixed with ordinary attributes.

> 
> This cannot break anything so I'll push this to -next tomorrow and
> submit to Linus next week

Agreed.

> 
>> Fixes: ca41bb3e21d7 ("[net/9p] Handle Zero Copy TREAD/RERROR case in !dotl case.")
> 
> This commit moves this code a bit, but the p9pdu_readf call predates
> it -- in this case the Fixes tag is probably not useful; this affects
> all maintained kernels.
> 
>> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
>> ---
>>   net/9p/client.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/9p/client.c b/net/9p/client.c
>> index 86bbc7147fc1..6c7cd765b714 100644
>> --- a/net/9p/client.c
>> +++ b/net/9p/client.c
>> @@ -540,12 +540,15 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
>>   		return 0;
>>   
>>   	if (!p9_is_proto_dotl(c)) {
>> -		char *ename;
>> +		char *ename = NULL;
>>   
>>   		err = p9pdu_readf(&req->rc, c->proto_version, "s?d",
>>   				  &ename, &ecode);
>> -		if (err)
>> +		if (err) {
>> +			if (ename != NULL)
>> +				kfree(ename);
> 
> Don't check for NULL before kfree - kfree does it.
> If that's the only remark you get I can fix it when applying the commit
> on my side.

I get it. I will revise it based on your and Christian's comments and 
send a v2.

Thanks,
Hangyu

> 
> 
>>   			goto out_err;
>> +		}
>>   
>>   		if (p9_is_proto_dotu(c) && ecode < 512)
>>   			err = -ecode;
>