* [PATCH bpf] libbpf: don't crash on object files with no symbol tables
@ 2021-08-31 16:58 Toke Høiland-Jørgensen
2021-08-31 22:45 ` Andrii Nakryiko
0 siblings, 1 reply; 3+ messages in thread
From: Toke Høiland-Jørgensen @ 2021-08-31 16:58 UTC (permalink / raw)
To: Andrii Nakryiko; +Cc: bpf, netdev, Toke Høiland-Jørgensen
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;
+
progs = obj->programs;
nr_progs = obj->nr_programs;
nr_syms = symbols->d_size / sizeof(GElf_Sym);
--
2.33.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH bpf] libbpf: don't crash on object files with no symbol tables
2021-08-31 16:58 [PATCH bpf] libbpf: don't crash on object files with no symbol tables Toke Høiland-Jørgensen
@ 2021-08-31 22:45 ` Andrii Nakryiko
2021-09-01 10:19 ` Toke Høiland-Jørgensen
0 siblings, 1 reply; 3+ messages in thread
From: Andrii Nakryiko @ 2021-08-31 22:45 UTC (permalink / raw)
To: Toke Høiland-Jørgensen; +Cc: Andrii Nakryiko, bpf, Networking
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
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH bpf] libbpf: don't crash on object files with no symbol tables
2021-08-31 22:45 ` Andrii Nakryiko
@ 2021-09-01 10:19 ` Toke Høiland-Jørgensen
0 siblings, 0 replies; 3+ messages in thread
From: Toke Høiland-Jørgensen @ 2021-09-01 10:19 UTC (permalink / raw)
To: Andrii Nakryiko; +Cc: Andrii Nakryiko, bpf, Networking
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
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-08-31 16:58 [PATCH bpf] libbpf: don't crash on object files with no symbol tables Toke Høiland-Jørgensen
2021-08-31 22:45 ` Andrii Nakryiko
2021-09-01 10:19 ` Toke Høiland-Jørgensen
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