From 6668ed271eaefaa63e686bdfbedaeb7b8e492722 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 10:43:19 +0200 Subject: selftests/bpf: Reject graph kptr use after RCU unlock Add a sleepable verifier test that loads a graph-node local kptr in an explicit RCU read-side critical section, then passes its node to bpf_rbtree_remove() after the section ends. Before the verifier fix, the stale NON_OWN_REF flag makes the node look like a live borrowed reference and the program is accepted. After the fix, the pointer is demoted without NON_OWN_REF and the graph kfunc argument is rejected. Also exercise a graph kptr loaded while a spin lock provides implicit RCU protection. The pointer must be invalidated when the lock is released, which guards the required ordering between non-owning-reference invalidation and RCU demotion. Update the existing fault-protected load test state description. The post-unlock pointer no longer carries NON_OWN_REF, but remains readable because the load is rewritten to use BPF_PROBE_MEM. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- include/net/gue.h | 120 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 120 insertions(+) create mode 100644 include/net/gue.h (limited to 'include/net/gue.h') diff --git a/include/net/gue.h b/include/net/gue.h new file mode 100644 index 000000000..caefd6da8 --- /dev/null +++ b/include/net/gue.h @@ -0,0 +1,120 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __NET_GUE_H +#define __NET_GUE_H + +/* Definitions for the GUE header, standard and private flags, lengths + * of optional fields are below. + * + * Diagram of GUE header: + * + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * |Ver|C| Hlen | Proto/ctype | Standard flags |P| + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * | | + * ~ Fields (optional) ~ + * | | + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * | Private flags (optional, P bit is set) | + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * | | + * ~ Private fields (optional) ~ + * | | + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * + * C bit indicates control message when set, data message when unset. + * For a control message, proto/ctype is interpreted as a type of + * control message. For data messages, proto/ctype is the IP protocol + * of the next header. + * + * P bit indicates private flags field is present. The private flags + * may refer to options placed after this field. + */ + +#include +#include + +struct guehdr { + union { + struct { +#if defined(__LITTLE_ENDIAN_BITFIELD) + __u8 hlen:5, + control:1, + version:2; +#elif defined (__BIG_ENDIAN_BITFIELD) + __u8 version:2, + control:1, + hlen:5; +#else +#error "Please fix " +#endif + __u8 proto_ctype; + __be16 flags; + }; + __be32 word; + }; +}; + +/* Standard flags in GUE header */ + +#define GUE_FLAG_PRIV htons(1<<0) /* Private flags are in options */ +#define GUE_LEN_PRIV 4 + +#define GUE_FLAGS_ALL (GUE_FLAG_PRIV) + +/* Private flags in the private option extension */ + +#define GUE_PFLAG_REMCSUM htonl(1U << 31) +#define GUE_PLEN_REMCSUM 4 + +#define GUE_PFLAGS_ALL (GUE_PFLAG_REMCSUM) + +/* Functions to compute options length corresponding to flags. + * If we ever have a lot of flags this can be potentially be + * converted to a more optimized algorithm (table lookup + * for instance). + */ +static inline size_t guehdr_flags_len(__be16 flags) +{ + return ((flags & GUE_FLAG_PRIV) ? GUE_LEN_PRIV : 0); +} + +static inline size_t guehdr_priv_flags_len(__be32 flags) +{ + return (flags & GUE_PFLAG_REMCSUM) ? GUE_PLEN_REMCSUM : 0; +} + +/* Validate standard and private flags. Returns non-zero (meaning invalid) + * if there is an unknown standard or private flags, or the options length for + * the flags exceeds the options length specific in hlen of the GUE header. + */ +static inline int validate_gue_flags(struct guehdr *guehdr, size_t optlen) +{ + __be16 flags = guehdr->flags; + size_t len; + + if (flags & ~GUE_FLAGS_ALL) + return 1; + + len = guehdr_flags_len(flags); + if (len > optlen) + return 1; + + if (flags & GUE_FLAG_PRIV) { + /* Private flags are last four bytes accounted in + * guehdr_flags_len + */ + __be32 pflags = *(__be32 *)((void *)&guehdr[1] + + len - GUE_LEN_PRIV); + + if (pflags & ~GUE_PFLAGS_ALL) + return 1; + + len += guehdr_priv_flags_len(pflags); + if (len > optlen) + return 1; + } + + return 0; +} + +#endif -- cgit v1.3.1