Please apply this to stable 5.10.y, and 5.15.y ---8<---
From: Kees Cook keescook@chromium.org
Upstream commit: 1a2fb220edca ("skbuff: Extract list pointers to silence compiler warnings")
Under both -Warray-bounds and the object_size sanitizer, the compiler is upset about accessing prev/next of sk_buff when the object it thinks it is coming from is sk_buff_head. The warning is a false positive due to the compiler taking a conservative approach, opting to warn at casting time rather than access time.
However, in support of enabling -Warray-bounds globally (which has found many real bugs), arrange things for sk_buff so that the compiler can unambiguously see that there is no intention to access anything except prev/next. Introduce and cast to a separate struct sk_buff_list, which contains _only_ the first two fields, silencing the warnings:
In file included from ./include/net/net_namespace.h:39, from ./include/linux/netdevice.h:37, from net/core/netpoll.c:17: net/core/netpoll.c: In function 'refill_skbs': ./include/linux/skbuff.h:2086:9: warning: array subscript 'struct sk_buff[0]' is partly outside array bounds of 'struct sk_buff_head[1]' [-Warray-bounds] 2086 | __skb_insert(newsk, next->prev, next, list); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ net/core/netpoll.c:49:28: note: while referencing 'skb_pool' 49 | static struct sk_buff_head skb_pool; | ^~~~~~~~
This also upsets UBSAN, which throws a runtime object-size-mismatch error complaining about skbuff queue helpers, as below, when the kernel is built with clang and -fsanitize=undefined flag set:
UBSAN: object-size-mismatch in ./include/linux/skbuff.h:2023:28 member access within address ffffc90000cb71c0 with insufficient space for an object of type 'struct sk_buff'
This change results in no executable instruction differences.
Signed-off-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20211207062758.2324338-1-keescook@chromium.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Tadeusz Struk tadeusz.struk@linaro.org --- include/linux/skbuff.h | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index acbf1875ad50..b7de22193ec8 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -289,9 +289,11 @@ struct tc_skb_ext { #endif
struct sk_buff_head { + struct_group_tagged(sk_buff_list, list, /* These two members must be first. */ struct sk_buff *next; struct sk_buff *prev; + );
__u32 qlen; spinlock_t lock; @@ -1906,8 +1908,8 @@ static inline void __skb_insert(struct sk_buff *newsk, */ WRITE_ONCE(newsk->next, next); WRITE_ONCE(newsk->prev, prev); - WRITE_ONCE(next->prev, newsk); - WRITE_ONCE(prev->next, newsk); + WRITE_ONCE(((struct sk_buff_list *)next)->prev, newsk); + WRITE_ONCE(((struct sk_buff_list *)prev)->next, newsk); WRITE_ONCE(list->qlen, list->qlen + 1); }
@@ -2003,7 +2005,7 @@ static inline void __skb_queue_after(struct sk_buff_head *list, struct sk_buff *prev, struct sk_buff *newsk) { - __skb_insert(newsk, prev, prev->next, list); + __skb_insert(newsk, prev, ((struct sk_buff_list *)prev)->next, list); }
void skb_append(struct sk_buff *old, struct sk_buff *newsk, @@ -2013,7 +2015,7 @@ static inline void __skb_queue_before(struct sk_buff_head *list, struct sk_buff *next, struct sk_buff *newsk) { - __skb_insert(newsk, next->prev, next, list); + __skb_insert(newsk, ((struct sk_buff_list *)next)->prev, next, list); }
/**