From 06ef0ccb5a36e1feba9b413ff59a04ecc4407c1c Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Mon, 18 Dec 2017 10:13:44 -0800 Subject: bpf/cgroup: fix a verification error for a CGROUP_DEVICE type prog The tools/testing/selftests/bpf test program test_dev_cgroup fails with the following error when compiled with llvm 6.0. (I did not try with earlier versions.) libbpf: load bpf program failed: Permission denied libbpf: -- BEGIN DUMP LOG --- libbpf: 0: (61) r2 = *(u32 *)(r1 +4) 1: (b7) r0 = 0 2: (55) if r2 != 0x1 goto pc+8 R0=inv0 R1=ctx(id=0,off=0,imm=0) R2=inv1 R10=fp0 3: (69) r2 = *(u16 *)(r1 +0) invalid bpf_context access off=0 size=2 ... The culprit is the following statement in dev_cgroup.c: short type = ctx->access_type & 0xFFFF; This code is typical as the ctx->access_type is assigned as below in kernel/bpf/cgroup.c: struct bpf_cgroup_dev_ctx ctx = { .access_type = (access << 16) | dev_type, .major = major, .minor = minor, }; The compiler converts it to u16 access while the verifier cgroup_dev_is_valid_access rejects any non u32 access. This patch permits the field access_type to be accessible with type u16 and u8 as well. Signed-off-by: Yonghong Song Tested-by: Roman Gushchin Signed-off-by: Daniel Borkmann --- include/uapi/linux/bpf.h | 3 ++- kernel/bpf/cgroup.c | 15 +++++++++++++-- 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index d01f1cb3cfc0..69eabfcb9bdb 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -1012,7 +1012,8 @@ struct bpf_perf_event_value { #define BPF_DEVCG_DEV_CHAR (1ULL << 1) struct bpf_cgroup_dev_ctx { - __u32 access_type; /* (access << 16) | type */ + /* access_type encoded as (BPF_DEVCG_ACC_* << 16) | BPF_DEVCG_DEV_* */ + __u32 access_type; __u32 major; __u32 minor; }; diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index b789ab78d28f..c1c0b60d3f2f 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -568,6 +568,8 @@ static bool cgroup_dev_is_valid_access(int off, int size, enum bpf_access_type type, struct bpf_insn_access_aux *info) { + const int size_default = sizeof(__u32); + if (type == BPF_WRITE) return false; @@ -576,8 +578,17 @@ static bool cgroup_dev_is_valid_access(int off, int size, /* The verifier guarantees that size > 0. */ if (off % size != 0) return false; - if (size != sizeof(__u32)) - return false; + + switch (off) { + case bpf_ctx_range(struct bpf_cgroup_dev_ctx, access_type): + bpf_ctx_record_field_size(info, size_default); + if (!bpf_ctx_narrow_access_ok(off, size, size_default)) + return false; + break; + default: + if (size != size_default) + return false; + } return true; } -- cgit v1.2.3-59-g8ed1b