net: add kcov handle to skb extensions

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.

Enable coverage-guided frame injection by adding kcov remote handle to
skb extensions. Default initialization in __alloc_skb and
__build_skb_around ensures that no socket buffer that was generated
during a system call will be missed.

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 during normal background network
processes or were intentionally injected from the user space.

Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index a828cf99c5215e132aa2105d9ba95d360afd4069..2d01b2bbb74651bc82e6f171bcbb6d0422c1f76c 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4150,6 +4150,9 @@ enum skb_ext_id {
 #endif
 #if IS_ENABLED(CONFIG_MPTCP)
        SKB_EXT_MPTCP,
+#endif
+#if IS_ENABLED(CONFIG_KCOV)
+       SKB_EXT_KCOV_HANDLE,
 #endif
        SKB_EXT_NUM, /* must be last */
 };
@@ -4605,5 +4608,35 @@ static inline void skb_reset_redirect(struct sk_buff *skb)
 #endif
 }
 
+#ifdef CONFIG_KCOV
+static inline void skb_set_kcov_handle(struct sk_buff *skb,
+                                      const u64 kcov_handle)
+{
+       /* Do not allocate skb extensions only to set kcov_handle to zero
+        * (as it is zero by default). However, if the extensions are
+        * already allocated, update kcov_handle anyway since
+        * skb_set_kcov_handle can be called to zero a previously set
+        * value.
+        */
+       if (skb_has_extensions(skb) || kcov_handle) {
+               u64 *kcov_handle_ptr = skb_ext_add(skb, SKB_EXT_KCOV_HANDLE);
+
+               if (kcov_handle_ptr)
+                       *kcov_handle_ptr = kcov_handle;
+       }
+}
+
+static inline u64 skb_get_kcov_handle(struct sk_buff *skb)
+{
+       u64 *kcov_handle = skb_ext_find(skb, SKB_EXT_KCOV_HANDLE);
+
+       return kcov_handle ? *kcov_handle : 0;
+}
+#else
+static inline void skb_set_kcov_handle(struct sk_buff *skb,
+                                      const u64 kcov_handle) { }
+static inline u64 skb_get_kcov_handle(struct sk_buff *skb) { return 0; }
+#endif /* CONFIG_KCOV */
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_SKBUFF_H */

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index d7a7bc3b6098287dc7af87b2c94d5304675401f3..d171a032db78d8894ab180e83aaaf5a693fefd14 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1870,6 +1870,7 @@ config KCOV
        depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
        select DEBUG_FS
        select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC
+       select SKB_EXTENSIONS
        help
          KCOV exposes kernel code coverage information in a form suitable
          for coverage-guided fuzzing (randomized testing).

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1ba8f01637441f868e19077c56d420573be7b6e9..c5e6c0b83a9266c4f5f1412df37fa744f13b423f 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -249,6 +249,9 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
 
                fclones->skb2.fclone = SKB_FCLONE_CLONE;
        }
+
+       skb_set_kcov_handle(skb, kcov_common_handle());
+
 out:
        return skb;
 nodata:
@@ -282,6 +285,8 @@ static struct sk_buff *__build_skb_around(struct sk_buff *skb,
        memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
        atomic_set(&shinfo->dataref, 1);
 
+       skb_set_kcov_handle(skb, kcov_common_handle());
+
        return skb;
 }
 
@@ -4203,6 +4208,9 @@ static const u8 skb_ext_type_len[] = {
 #if IS_ENABLED(CONFIG_MPTCP)
        [SKB_EXT_MPTCP] = SKB_EXT_CHUNKSIZEOF(struct mptcp_ext),
 #endif
+#if IS_ENABLED(CONFIG_KCOV)
+       [SKB_EXT_KCOV_HANDLE] = SKB_EXT_CHUNKSIZEOF(u64),
+#endif
 };
 
 static __always_inline unsigned int skb_ext_total_length(void)
@@ -4219,6 +4227,9 @@ static __always_inline unsigned int skb_ext_total_length(void)
 #endif
 #if IS_ENABLED(CONFIG_MPTCP)
                skb_ext_type_len[SKB_EXT_MPTCP] +
+#endif
+#if IS_ENABLED(CONFIG_KCOV)
+               skb_ext_type_len[SKB_EXT_KCOV_HANDLE] +
 #endif
                0;
 }