linux-kernel - Re: [PATCH bpf] bpf: add check for invalid name in btf_name_valid

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Message-ID: <bd8a6dc3e52369a30c73578ea1144a48f736f393.camel@gmail.com>
Date: Fri, 30 Aug 2024 02:42:19 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Jeongjun Park <aha310510@...il.com>
Cc: alexei.starovoitov@...il.com, andrii@...nel.org, ast@...nel.org, 
	bpf@...r.kernel.org, daniel@...earbox.net, haoluo@...gle.com, 
	john.fastabend@...il.com, jolsa@...nel.org, kpsingh@...nel.org, 
	linux-kernel@...r.kernel.org, martin.lau@...ux.dev, sdf@...ichev.me, 
	song@...nel.org, yonghong.song@...ux.dev
Subject: Re: [PATCH bpf] bpf: add check for invalid name in
 btf_name_valid_section()

On Fri, 2024-08-30 at 11:03 +0900, Jeongjun Park wrote:

[...]

> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index edad152cee8e..d583d76fcace 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -820,7 +820,6 @@ static bool btf_name_valid_section(const struct btf *btf, u32 offset)
> > 
> >        /* set a limit on identifier length */
> >        src_limit = src + KSYM_NAME_LEN;
> > -       src++;
> >        while (*src && src < src_limit) {
> >                if (!isprint(*src))
> >                        return false;
> 
> However, this patch is logically flawed. 
> It will return true for invalid names with 
> length 1 and src[0] being NULL. So I think 
> it's better to stick with the original patch.

Fair enough, however the isprint check should be done for the first character.
So the full fix is a combination :)

--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -818,9 +818,11 @@ static bool btf_name_valid_section(const struct btf *btf, u32 offset)
        const char *src = btf_str_by_offset(btf, offset);
        const char *src_limit;
 
+       if (!*src)
+               return false;
+
        /* set a limit on identifier length */
        src_limit = src + KSYM_NAME_LEN;
-       src++;
        while (*src && src < src_limit) {
                if (!isprint(*src))
                        return false;


And corresponding test cases (tools/testing/selftests/bpf/prog_tests/btf.c):

{
	.descr = "datasec: name with non-printable first char not is ok",
	.raw_types = {
		/* int */
		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),  /* [1] */
		/* VAR x */                                     /* [2] */
		BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_VAR, 0, 0), 1),
		BTF_VAR_STATIC,
		/* DATASEC ?.data */                            /* [3] */
		BTF_TYPE_ENC(3, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 1), 4),
		BTF_VAR_SECINFO_ENC(2, 0, 4),
		BTF_END_RAW,
	},
	BTF_STR_SEC("\0x\0\7foo"),
	.err_str = "Invalid name",
	.btf_load_err = true,
},{
	.descr = "datasec: name '\\0' is not ok",
	.raw_types = {
		/* int */
		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),  /* [1] */
		/* VAR x */                                     /* [2] */
		BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_VAR, 0, 0), 1),
		BTF_VAR_STATIC,
		/* DATASEC \0 */                                /* [3] */
		BTF_TYPE_ENC(3, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 1), 4),
		BTF_VAR_SECINFO_ENC(2, 0, 4),
		BTF_END_RAW,
	},
	BTF_STR_SEC("\0x\0"),
	.err_str = "Invalid name",
	.btf_load_err = true,
},

Could you please resend your patch as a patch-set fix + selftests update?