[PATCH 4.14 03/17] esp: Fix possible buffer overflow in ESP transformation

Greg Kroah-Hartman
2022-03-25T15:07:46Z

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

commit ebe48d368e97d007bfeb76fcb065d6cfc4c96645 upstream.

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>
Signed-off-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/esp.h | 2 ++
include/net/sock.h | 3 +++
net/core/sock.c | 3 ---
net/ipv4/esp4.c | 5 +++++
net/ipv6/esp6.c | 5 +++++
5 files changed, 15 insertions(+), 3 deletions(-)

--- 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)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2438,4 +2438,7 @@ extern int sysctl_optmem_max;
extern __u32 sysctl_wmem_default;
extern __u32 sysctl_rmem_default;

+/* On 32bit arches, an skb frag is limited to 2^15 */
+#define SKB_FRAG_PAGE_ORDER get_order(32768)
+
#endif /* _SOCK_H */
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2193,9 +2193,6 @@ static void sk_leave_memory_pressure(str
}
}

-/* On 32bit arches, an skb frag is limited to 2^15 */
-#define SKB_FRAG_PAGE_ORDER get_order(32768)
-
/**
* skb_page_frag_refill - check that a page_frag contains enough room
* @sz: minimum size of the fragment we want to get
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -257,6 +257,7 @@ int esp_output_head(struct xfrm_state *x
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
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;
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -223,6 +223,11 @@ int esp6_output_head(struct xfrm_state *
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)) {