[SRU,Bionic] esp: Fix possible buffer overflow in ESP transformation

From: Steffen Klassert <steffen.klassert@secunet.com>

The maximum message size that can be send is bigger than
the  maximum site that skb_page_frag_refill can allocate.
So it is possible to write beyond the allocated buffer.

Fix this by doing a fallback to COW in that case.

v2:

Avoid get get_order() costs as suggested by Linus Torvalds.

Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
Fixes: 03e2a30f6a27 ("esp6: Avoid skb_cow_data whenever possible")
Reported-by: valis <sec@valis.email>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
(backported from commit ebe48d368e97d007bfeb76fcb065d6cfc4c96645)
[cascardo: there was not x->encap test on esp6_output_head because of missing commit
 0146dca70b877b73c5fd9c67912b8a0ca8a7bac7]
[cascardo: add SKB_FRAG_PAGE_ORDER to include/net/sock.h]
CVE-2022-27666
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
---
 include/net/esp.h  | 2 ++
 include/net/sock.h | 2 ++
 net/ipv4/esp4.c    | 5 +++++
 net/ipv6/esp6.c    | 5 +++++
 4 files changed, 14 insertions(+)

Applied to bionic:linux/master-next.

Thanks,
- Luke

On Thu, Mar 24, 2022 at 4:16 AM Thadeu Lima de Souza Cascardo <
cascardo@canonical.com> wrote:

> From: Steffen Klassert <steffen.klassert@secunet.com>
>
> The maximum message size that can be send is bigger than
> the  maximum site that skb_page_frag_refill can allocate.
> So it is possible to write beyond the allocated buffer.
>
> Fix this by doing a fallback to COW in that case.
>
> v2:
>
> Avoid get get_order() costs as suggested by Linus Torvalds.
>
> Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
> Fixes: 03e2a30f6a27 ("esp6: Avoid skb_cow_data whenever possible")
> Reported-by: valis <sec@valis.email>
> Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
> (backported from commit ebe48d368e97d007bfeb76fcb065d6cfc4c96645)
> [cascardo: there was not x->encap test on esp6_output_head because of
> missing commit
>  0146dca70b877b73c5fd9c67912b8a0ca8a7bac7]
> [cascardo: add SKB_FRAG_PAGE_ORDER to include/net/sock.h]
> CVE-2022-27666
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> ---
>  include/net/esp.h  | 2 ++
>  include/net/sock.h | 2 ++
>  net/ipv4/esp4.c    | 5 +++++
>  net/ipv6/esp6.c    | 5 +++++
>  4 files changed, 14 insertions(+)
>
> diff --git a/include/net/esp.h b/include/net/esp.h
> index 117652eb6ea3..465e38890ee9 100644
> --- a/include/net/esp.h
> +++ b/include/net/esp.h
> @@ -4,6 +4,8 @@
>
>  #include <linux/skbuff.h>
>
> +#define ESP_SKB_FRAG_MAXSIZE (PAGE_SIZE << SKB_FRAG_PAGE_ORDER)
> +
>  struct ip_esp_hdr;
>
>  static inline struct ip_esp_hdr *ip_esp_hdr(const struct sk_buff *skb)
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 79f9b7ee4e45..8dc208d54232 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2452,6 +2452,8 @@ extern int sysctl_optmem_max;
>  extern __u32 sysctl_wmem_default;
>  extern __u32 sysctl_rmem_default;
>
> +#define SKB_FRAG_PAGE_ORDER    get_order(32768)
> +
>  static inline int sk_get_wmem0(const struct sock *sk, const struct proto
> *proto)
>  {
>         /* Does this proto have per netns sysctl_wmem ? */
> diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
> index d8151c72205f..2dc2887a0e84 100644
> --- a/net/ipv4/esp4.c
> +++ b/net/ipv4/esp4.c
> @@ -257,6 +257,7 @@ int esp_output_head(struct xfrm_state *x, struct
> sk_buff *skb, struct esp_info *
>         struct page *page;
>         struct sk_buff *trailer;
>         int tailen = esp->tailen;
> +       unsigned int allocsz;
>
>         /* this is non-NULL only with UDP Encapsulation */
>         if (x->encap) {
> @@ -266,6 +267,10 @@ int esp_output_head(struct xfrm_state *x, struct
> sk_buff *skb, struct esp_info *
>                         return err;
>         }
>
> +       allocsz = ALIGN(skb->data_len + tailen, L1_CACHE_BYTES);
> +       if (allocsz > ESP_SKB_FRAG_MAXSIZE)
> +               goto cow;
> +
>         if (!skb_cloned(skb)) {
>                 if (tailen <= skb_tailroom(skb)) {
>                         nfrags = 1;
> diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
> index 3eb167ad1ce6..cbc663756841 100644
> --- a/net/ipv6/esp6.c
> +++ b/net/ipv6/esp6.c
> @@ -223,6 +223,11 @@ int esp6_output_head(struct xfrm_state *x, struct
> sk_buff *skb, struct esp_info
>         struct page *page;
>         struct sk_buff *trailer;
>         int tailen = esp->tailen;
> +       unsigned int allocsz;
> +
> +       allocsz = ALIGN(skb->data_len + tailen, L1_CACHE_BYTES);
> +       if (allocsz > ESP_SKB_FRAG_MAXSIZE)
> +               goto cow;
>
>         if (!skb_cloned(skb)) {
>                 if (tailen <= skb_tailroom(skb)) {
> --
> 2.32.0
>
>
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