Re: [PATCH] cxl: Fix null pointer dereference in cxl_get_fd

[Kunwu Chan]

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@xxxxxxxxxx>
> > ---
> >   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))