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[bpf] libbpf: don't crash on object files with no symbol tables

Message ID 20210831165802.168776-1-toke@redhat.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series [bpf] libbpf: don't crash on object files with no symbol tables | expand

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netdev/checkpatch warning WARNING: 'overriden' may be misspelled - perhaps 'overridden'?
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bpf/vmtest-bpf success Kernel LATEST + selftests

Commit Message

Toke Høiland-Jørgensen Aug. 31, 2021, 4:58 p.m. UTC
If libbpf encounters an ELF file that has been stripped of its symbol
table, it will crash in bpf_object__add_programs() when trying to
dereference the obj->efile.symbols pointer. Add a check and return to avoid
this.

Fixes: 6245947c1b3c ("libbpf: Allow gaps in BPF program sections to support overriden weak functions")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 tools/lib/bpf/libbpf.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Andrii Nakryiko Aug. 31, 2021, 10:45 p.m. UTC | #1
On Tue, Aug 31, 2021 at 9:58 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> If libbpf encounters an ELF file that has been stripped of its symbol
> table, it will crash in bpf_object__add_programs() when trying to
> dereference the obj->efile.symbols pointer. Add a check and return to avoid
> this.
>
> Fixes: 6245947c1b3c ("libbpf: Allow gaps in BPF program sections to support overriden weak functions")
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---
>  tools/lib/bpf/libbpf.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6f5e2757bb3c..4cd102affeef 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -668,6 +668,9 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
>         const char *name;
>         GElf_Sym sym;
>
> +       if (!symbols)
> +               return -ENOENT;
> +

The more logical place to do this check is in
bpf_object__elf_collect(). Can you add this there? We can also include
helpful error message.

But I'm also curious which Clang version is being used to cause no ELF
symbols being generated?

>         progs = obj->programs;
>         nr_progs = obj->nr_programs;
>         nr_syms = symbols->d_size / sizeof(GElf_Sym);
> --
> 2.33.0
>
Toke Høiland-Jørgensen Sept. 1, 2021, 10:19 a.m. UTC | #2
Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:

> On Tue, Aug 31, 2021 at 9:58 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>>
>> If libbpf encounters an ELF file that has been stripped of its symbol
>> table, it will crash in bpf_object__add_programs() when trying to
>> dereference the obj->efile.symbols pointer. Add a check and return to avoid
>> this.
>>
>> Fixes: 6245947c1b3c ("libbpf: Allow gaps in BPF program sections to support overriden weak functions")
>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> ---
>>  tools/lib/bpf/libbpf.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 6f5e2757bb3c..4cd102affeef 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -668,6 +668,9 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
>>         const char *name;
>>         GElf_Sym sym;
>>
>> +       if (!symbols)
>> +               return -ENOENT;
>> +
>
> The more logical place to do this check is in
> bpf_object__elf_collect(). Can you add this there? We can also include
> helpful error message.

Sure, can do.

> But I'm also curious which Clang version is being used to cause no ELF
> symbols being generated?

It's not Clang. I was debugging an issue with 'strip' mangling BPF
object files and ran into this after trying to load an object file that
had been run through a full 'strip bpf_object.o' (whereas 'strip -g
bpf_object.o' works fine, except for that one bug I'm looking at).

-Toke
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6f5e2757bb3c..4cd102affeef 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -668,6 +668,9 @@  bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
 	const char *name;
 	GElf_Sym sym;
 
+	if (!symbols)
+		return -ENOENT;
+
 	progs = obj->programs;
 	nr_progs = obj->nr_programs;
 	nr_syms = symbols->d_size / sizeof(GElf_Sym);