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authorJiri Olsa <jolsa@kernel.org>2020-01-23 17:15:06 +0100
committerAlexei Starovoitov <ast@kernel.org>2020-01-25 07:12:40 -0800
commit84ad7a7ab69f112c0c4b878c9be91b950a1fb1f8 (patch)
treeeb5de4f71b8c7f558e487755fe753f99cbe2f205 /kernel
parent35b9211c0a2427e8f39e534f442f43804fc8d5ca (diff)
bpf: Allow BTF ctx access for string pointers
When accessing the context we allow access to arguments with scalar type and pointer to struct. But we deny access for pointer to scalar type, which is the case for many functions. Alexei suggested to take conservative approach and allow currently only string pointer access, which is the case for most functions now: Adding check if the pointer is to string type and allow access to it. Suggested-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Jiri Olsa <jolsa@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200123161508.915203-2-jolsa@kernel.org
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/btf.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 32963b6d5a9c..b7c1660fb594 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3669,6 +3669,19 @@ struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog)
}
}
+static bool is_string_ptr(struct btf *btf, const struct btf_type *t)
+{
+ /* t comes in already as a pointer */
+ t = btf_type_by_id(btf, t->type);
+
+ /* allow const */
+ if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
+ t = btf_type_by_id(btf, t->type);
+
+ /* char, signed char, unsigned char */
+ return btf_type_is_int(t) && t->size == 1;
+}
+
bool btf_ctx_access(int off, int size, enum bpf_access_type type,
const struct bpf_prog *prog,
struct bpf_insn_access_aux *info)
@@ -3735,6 +3748,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
*/
return true;
+ if (is_string_ptr(btf, t))
+ return true;
+
/* this is a pointer to another type */
info->reg_type = PTR_TO_BTF_ID;