From: Aleksandr Nogikh <nogikh@xxxxxxxxxx> Remote KCOV coverage collection enables coverage-guided fuzzing of the code that is not reachable during normal system call execution. It is especially helpful for fuzzing networking subsystems, where it is common to perform packet handling in separate work queues even for the packets that originated directly from the user space. More details can be found in Documentation/dev-tools/kcov.rst. Enable coverage-guided frame injection by adding a kcov_handle parameter to sk_buff structure. Initializate this field in __alloc_skb to kcov_common_handle() so that no socket buffer that was generated during a system call is missed. For sk_buffs that were allocated in an interrupt context, kcov_handle will be initialized to 0. Code that is of interest and that performs packet processing should be annotated with kcov_remote_start()/kcov_remote_stop(). An alternative approach is to determine kcov_handle solely on the basis of the device/interface that received the specific socket buffer. However, in this case it would be impossible to distinguish between packets that originated from normal background network processes and those that were intentionally injected from the user space. Signed-off-by: Aleksandr Nogikh <nogikh@xxxxxxxxxx> Signed-off-by: Marco Elver <elver@xxxxxxxxxx> --- v6: * Revert usage of skb extensions in favour of directly storing the kcov_handle in in sk_buff. skb extensions were leading to a memory leak as reported by Ido Schimmel: https://lore.kernel.org/linux-wireless/20201121160941.GA485907@xxxxxxxxxxxx/ --- include/linux/skbuff.h | 21 +++++++++++++++++++++ net/core/skbuff.c | 1 + 2 files changed, 22 insertions(+) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index a828cf99c521..5639f27e05ef 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -701,6 +701,7 @@ typedef unsigned char *sk_buff_data_t; * @transport_header: Transport layer header * @network_header: Network layer header * @mac_header: Link layer header + * @kcov_handle: KCOV remote handle for remote coverage collection * @tail: Tail pointer * @end: End pointer * @head: Head of buffer @@ -904,6 +905,10 @@ struct sk_buff { __u16 network_header; __u16 mac_header; +#ifdef CONFIG_KCOV + u64 kcov_handle; +#endif + /* private: */ __u32 headers_end[0]; /* public: */ @@ -4605,5 +4610,21 @@ static inline void skb_reset_redirect(struct sk_buff *skb) #endif } +static inline void skb_set_kcov_handle(struct sk_buff *skb, const u64 kcov_handle) +{ +#ifdef CONFIG_KCOV + skb->kcov_handle = kcov_handle; +#endif +} + +static inline u64 skb_get_kcov_handle(struct sk_buff *skb) +{ +#ifdef CONFIG_KCOV + return skb->kcov_handle; +#else + return 0; +#endif +} + #endif /* __KERNEL__ */ #endif /* _LINUX_SKBUFF_H */ diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 1ba8f0163744..2f27635c3e97 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -233,6 +233,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, skb->end = skb->tail + size; skb->mac_header = (typeof(skb->mac_header))~0U; skb->transport_header = (typeof(skb->transport_header))~0U; + skb_set_kcov_handle(skb, kcov_common_handle()); /* make sure we initialize shinfo sequentially */ shinfo = skb_shinfo(skb); -- 2.29.2.454.gaff20da3a2-goog
