Re: [PATCH] Fix null pointer dereference in vector_user_bpf

From: Anton Ivanov <anton.ivanov@cambridgegreys.com>
To: "Gaurav Singh" <gaurav1086@gmail.com>,
	"Jeff Dike" <jdike@addtoit.com>,
	"Richard Weinberger" <richard@nod.at>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"Andrii Nakryiko" <andriin@fb.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@chromium.org>,
	"Alex Dewar" <alex.dewar@gmx.co.uk>,
	"Marc-André Lureau" <marcandre.lureau@redhat.com>,
	"open list:USER-MODE LINUX (UML)" <linux-um@lists.infradead.org>,
	"open list" <linux-kernel@vger.kernel.org>,
	"open list:BPF (Safe dynamic programs and tools)"
	<netdev@vger.kernel.org>,
	"open list:BPF (Safe dynamic programs and tools)"
	<bpf@vger.kernel.org>
Subject: Re: [PATCH] Fix null pointer dereference in vector_user_bpf
Date: Sun, 14 Jun 2020 07:38:51 +0100	[thread overview]
Message-ID: <39158d22-9997-32ef-c599-7e6a98988a38@cambridgegreys.com> (raw)
In-Reply-To: <20200614012001.18468-1-gaurav1086@gmail.com>

On 14/06/2020 02:19, Gaurav Singh wrote:
> The bpf_prog is being checked for !NULL after uml_kmalloc
> but later its used directly for example:
> bpf_prog->filter = bpf and is also later returned upon
> success. Fix this, do a NULL check and return right away.
> 
> Signed-off-by: Gaurav Singh <gaurav1086@gmail.com>
> ---
>   arch/um/drivers/vector_user.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/um/drivers/vector_user.c b/arch/um/drivers/vector_user.c
> index c4a0f26b2824..0e6d6717bf73 100644
> --- a/arch/um/drivers/vector_user.c
> +++ b/arch/um/drivers/vector_user.c
> @@ -789,10 +789,12 @@ void *uml_vector_user_bpf(char *filename)
>   		return false;
>   	}
>   	bpf_prog = uml_kmalloc(sizeof(struct sock_fprog), UM_GFP_KERNEL);
> -	if (bpf_prog != NULL) {
> -		bpf_prog->len = statbuf.st_size / sizeof(struct sock_filter);
> -		bpf_prog->filter = NULL;
> +	if (bpf_prog == NULL) {
> +		printk(KERN_ERR "Failed to allocate bpf prog buffer");
> +		return NULL;
>   	}
> +	bpf_prog->len = statbuf.st_size / sizeof(struct sock_filter);
> +	bpf_prog->filter = NULL;
>   	ffd = os_open_file(filename, of_read(OPENFLAGS()), 0);
>   	if (ffd < 0) {
>   		printk(KERN_ERR "Error %d opening bpf file", -errno);
> 

Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/