From: Alexei Starovoitov <ast@kernel.org>
Date: Fri, 31 Jan 2020 16:03:14 -0800
Subject: bpf: Fix modifier skipping logic
Patch-mainline: v5.6-rc1
Git-commit: 257af63d7f84f0672aa6a24b5511871f00741f19
References: bsc#1155518
Fix the way modifiers are skipped while walking pointers. Otherwise second
level dereferences of 'const struct foo *' will be rejected by the verifier.
Fixes: 9e15db66136a ("bpf: Implement accurate raw_tp context access via BTF")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200201000314.261392-1-ast@kernel.org
Acked-by: Gary Lin <glin@suse.com>
NOTE: This patch is modified to add the equivalent implementation of
btf_type_skip_modifiers() in btf_struct_access().
---
kernel/bpf/btf.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3838,6 +3838,7 @@ again:
if (btf_type_is_ptr(mtype)) {
const struct btf_type *stype;
+ u32 id;
if (msize != size || off != moff) {
bpf_log(log,
@@ -3846,12 +3847,15 @@ again:
return -EACCES;
}
+ id = mtype->type;
stype = btf_type_by_id(btf_vmlinux, mtype->type);
/* skip modifiers */
- while (btf_type_is_modifier(stype))
+ while (btf_type_is_modifier(stype)) {
+ id = stype->type;
stype = btf_type_by_id(btf_vmlinux, stype->type);
+ }
if (btf_type_is_struct(stype)) {
- *next_btf_id = mtype->type;
+ *next_btf_id = id;
return PTR_TO_BTF_ID;
}
}