linux-kernel - Re: [PATCH] cxl: Fix null pointer dereference in cxl_get

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Message-ID: <7be4a5ac-d0b8-4f5d-848a-b54ab3c67228@kylinos.cn>
Date:   Tue, 5 Dec 2023 17:28:30 +0800
From:   Kunwu Chan <chentao@...inos.cn>
To:     Frederic Barrat <fbarrat@...ux.ibm.com>, ajd@...ux.ibm.com,
        arnd@...db.de, gregkh@...uxfoundation.org, mpe@...erman.id.au,
        mrochs@...ux.vnet.ibm.com
Cc:     kunwu.chan@...mail.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cxl: Fix null pointer dereference in cxl_get_fd

Hi Fred,
Thanks for your reply.


But there is a question, whether we should return an error code in error 
path so that the caller of the 'cxl_get_fd' can know the specific 
reason. rather than just return NULL.
Such as:
-       int rc, flags, fdtmp;
+       int rc = 0, flags, fdtmp;
         char *name = NULL;

         /* only allow one per context */
-       if (ctx->mapping)
-               return ERR_PTR(-EEXIST);
+       if (ctx->mapping) {
+               rc = -EEXIST;
+               goto err;
+       }

         flags = O_RDWR | O_CLOEXEC;

         /* This code is similar to anon_inode_getfd() */
         rc = get_unused_fd_flags(flags);
-       if (rc < 0)
-               return ERR_PTR(rc);
+       if (rc < 0) {
+               goto err;
+       }
         fdtmp = rc;



         name = kasprintf(GFP_KERNEL, "cxl:%d", ctx->pe);
+        if (!name) {
+               rc = -ENOMEM;
+               goto err_fd;
+        }
         file = cxl_getfile(name, fops, ctx, flags);
         kfree(name);
@@ -434,6 +437,9 @@ struct file *cxl_get_fd(struct cxl_context *ctx, 
struct file_operations *fops,

  err_fd:
         put_unused_fd(fdtmp);
+err:
+       if (rc)
+               return ERR_PTR(rc);
         return NULL;


Thanks again,
Kunwu

On 2023/12/4 18:43, Frederic Barrat wrote:
> 
> 
> On 04/12/2023 03:07, Kunwu Chan wrote:
>> kasprintf() returns a pointer to dynamically allocated memory
>> which can be NULL upon failure.
>>
>> Fixes: bdecf76e319a ("cxl: Fix coredump generation when cxl_get_fd() 
>> is used")
>> Signed-off-by: Kunwu Chan <chentao@...inos.cn>
>> ---
>>   drivers/misc/cxl/api.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/misc/cxl/api.c b/drivers/misc/cxl/api.c
>> index d85c56530863..bfd7ccd4d7e1 100644
>> --- a/drivers/misc/cxl/api.c
>> +++ b/drivers/misc/cxl/api.c
>> @@ -419,6 +419,10 @@ struct file *cxl_get_fd(struct cxl_context *ctx, 
>> struct file_operations *fops,
>>           fops = (struct file_operations *)&afu_fops;
>>       name = kasprintf(GFP_KERNEL, "cxl:%d", ctx->pe);
>> +    if (!name) {
>> +        put_unused_fd(fdtmp);
>> +        return ERR_PTR(-ENOMEM);
>> +    }
> 
> 
> That works, but you might as well follow the existing error path:
> 
>      name = kasprintf(GFP_KERNEL, "cxl:%d", ctx->pe);
>      if (!name)
>          goto err_fd;
> 
>    Fred
> 
> 
>>       file = cxl_getfile(name, fops, ctx, flags);
>>       kfree(name);
>>       if (IS_ERR(file))