[PATCH bpf] xsk: Fix unaligned descriptor validation

[PATCH bpf] xsk: Fix unaligned descriptor validation

[Kal Conley]

Make sure unaligned descriptors that straddle the end of the UMEM are
considered invalid. Currently, descriptor validation is broken for
zero-copy mode which only checks descriptors at page granularity.
Descriptors that cross the end of the UMEM but not a page boundary may
be therefore incorrectly considered valid. The check needs to happen
before the page boundary and contiguity checks in
xp_desc_crosses_non_contig_pg. Do this check in
xp_unaligned_validate_desc instead like xp_check_unaligned already does.

Fixes: 2b43470add8c ("xsk: Introduce AF_XDP buffer allocation API")
Signed-off-by: Kal Conley <kal.conley@dectris.com>
---
 include/net/xsk_buff_pool.h | 9 ++-------
 net/xdp/xsk_queue.h         | 1 +
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
index 3e952e569418..d318c769b445 100644
--- a/include/net/xsk_buff_pool.h
+++ b/include/net/xsk_buff_pool.h
@@ -180,13 +180,8 @@ static inline bool xp_desc_crosses_non_contig_pg(struct xsk_buff_pool *pool,
 	if (likely(!cross_pg))
 		return false;
 
-	if (pool->dma_pages_cnt) {
-		return !(pool->dma_pages[addr >> PAGE_SHIFT] &
-			 XSK_NEXT_PG_CONTIG_MASK);
-	}
-
-	/* skb path */
-	return addr + len > pool->addrs_cnt;
+	return pool->dma_pages_cnt &&
+	       !(pool->dma_pages[addr >> PAGE_SHIFT] & XSK_NEXT_PG_CONTIG_MASK);
 }
 
 static inline u64 xp_aligned_extract_addr(struct xsk_buff_pool *pool, u64 addr)
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index bfb2a7e50c26..66c6f57c9c44 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -162,6 +162,7 @@ static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
 		return false;
 
 	if (base_addr >= pool->addrs_cnt || addr >= pool->addrs_cnt ||
+	    addr + desc->len > pool->addrs_cnt ||
 	    xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
 		return false;
 
-- 
2.39.2

Re: [PATCH bpf] xsk: Fix unaligned descriptor validation

[Magnus Karlsson]

On Mon, 3 Apr 2023 at 16:38, Kal Conley <kal.conley@dectris.com> wrote:
>
> Make sure unaligned descriptors that straddle the end of the UMEM are
> considered invalid. Currently, descriptor validation is broken for
> zero-copy mode which only checks descriptors at page granularity.
> Descriptors that cross the end of the UMEM but not a page boundary may
> be therefore incorrectly considered valid. The check needs to happen
> before the page boundary and contiguity checks in
> xp_desc_crosses_non_contig_pg. Do this check in
> xp_unaligned_validate_desc instead like xp_check_unaligned already does.

Thanks for catching this Kal.

Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

> Fixes: 2b43470add8c ("xsk: Introduce AF_XDP buffer allocation API")
> Signed-off-by: Kal Conley <kal.conley@dectris.com>
> ---
>  include/net/xsk_buff_pool.h | 9 ++-------
>  net/xdp/xsk_queue.h         | 1 +
>  2 files changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
> index 3e952e569418..d318c769b445 100644
> --- a/include/net/xsk_buff_pool.h
> +++ b/include/net/xsk_buff_pool.h
> @@ -180,13 +180,8 @@ static inline bool xp_desc_crosses_non_contig_pg(struct xsk_buff_pool *pool,
>         if (likely(!cross_pg))
>                 return false;
>
> -       if (pool->dma_pages_cnt) {
> -               return !(pool->dma_pages[addr >> PAGE_SHIFT] &
> -                        XSK_NEXT_PG_CONTIG_MASK);
> -       }
> -
> -       /* skb path */
> -       return addr + len > pool->addrs_cnt;
> +       return pool->dma_pages_cnt &&
> +              !(pool->dma_pages[addr >> PAGE_SHIFT] & XSK_NEXT_PG_CONTIG_MASK);
>  }
>
>  static inline u64 xp_aligned_extract_addr(struct xsk_buff_pool *pool, u64 addr)
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index bfb2a7e50c26..66c6f57c9c44 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -162,6 +162,7 @@ static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
>                 return false;
>
>         if (base_addr >= pool->addrs_cnt || addr >= pool->addrs_cnt ||
> +           addr + desc->len > pool->addrs_cnt ||
>             xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
>                 return false;
>
> --
> 2.39.2
>

Re: [PATCH bpf] xsk: Fix unaligned descriptor validation

[Martin KaFai Lau]

On 4/3/23 11:25 PM, Magnus Karlsson wrote:
> On Mon, 3 Apr 2023 at 16:38, Kal Conley <kal.conley@dectris.com> wrote:
>>
>> Make sure unaligned descriptors that straddle the end of the UMEM are
>> considered invalid. Currently, descriptor validation is broken for
>> zero-copy mode which only checks descriptors at page granularity.
>> Descriptors that cross the end of the UMEM but not a page boundary may
>> be therefore incorrectly considered valid. The check needs to happen
>> before the page boundary and contiguity checks in
>> xp_desc_crosses_non_contig_pg. Do this check in
>> xp_unaligned_validate_desc instead like xp_check_unaligned already does.
> 
> Thanks for catching this Kal.
> 
> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

Is this case covered by an existing test?

Re: [PATCH bpf] xsk: Fix unaligned descriptor validation

[Kal Cutter Conley]

> Is this case covered by an existing test?
>

No. I submitted a test but I was asked to make minor changes to it. I
plan to submit the test once this gets picked up on bpf-next.

Re: [PATCH bpf] xsk: Fix unaligned descriptor validation

[Martin KaFai Lau]

On 4/5/23 12:48 PM, Kal Cutter Conley wrote:
>> Is this case covered by an existing test?
>>
> 
> No. I submitted a test but I was asked to make minor changes to it. I
> plan to submit the test once this gets picked up on bpf-next.

Since you already have a test case, it is better to submit them together such 
that this case can be covered earlier than later.

Other xskxceiver fixes have already landed to bpf-next. imo, I think for this 
particular case, bpf-next for both the fix and the test is fine.

Re: [PATCH bpf] xsk: Fix unaligned descriptor validation

[Kal Cutter Conley]

> Since you already have a test case, it is better to submit them together such
> that this case can be covered earlier than later.
>
> Other xskxceiver fixes have already landed to bpf-next. imo, I think for this
> particular case, bpf-next for both the fix and the test is fine.

Done. See: https://lore.kernel.org/all/20230405235920.7305-1-kal.conley@dectris.com/