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 <yhs@fb.com>
Tested-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d01f1cb..69eabfc 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;
};