[PATCH bpf-next] libbpf: fix hypothetical STT_SECTION extern NULL deref case

[PATCH bpf-next] libbpf: fix hypothetical STT_SECTION extern NULL deref case

[Andrii Nakryiko]

Fix theoretical NULL dereference in linker when resolving *extern*
STT_SECTION symbol against not-yet-existing ELF section. Not sure if
it's possible in practice for valid ELF object files (this would require
embedded assembly manipulations, at which point BTF will be missing),
but fix the s/dst_sym/dst_sec/ typo guarding this condition anyways.

Fixes: faf6ed321cf6 ("libbpf: Add BPF static linker APIs")
Fixes: a46349227cd8 ("libbpf: Add linker extern resolution support for functions and global variables")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/linker.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index b52f71c59616..800e0ef09c37 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -2163,7 +2163,7 @@ static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
 
 	obj->sym_map[src_sym_idx] = dst_sym_idx;
 
-	if (sym_type == STT_SECTION && dst_sym) {
+	if (sym_type == STT_SECTION && dst_sec) {
 		dst_sec->sec_sym_idx = dst_sym_idx;
 		dst_sym->st_value = 0;
 	}
-- 
2.43.5

Re: [PATCH bpf-next] libbpf: fix hypothetical STT_SECTION extern NULL deref case

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Wed, 19 Feb 2025 16:28:21 -0800 you wrote:
> Fix theoretical NULL dereference in linker when resolving *extern*
> STT_SECTION symbol against not-yet-existing ELF section. Not sure if
> it's possible in practice for valid ELF object files (this would require
> embedded assembly manipulations, at which point BTF will be missing),
> but fix the s/dst_sym/dst_sec/ typo guarding this condition anyways.
> 
> Fixes: faf6ed321cf6 ("libbpf: Add BPF static linker APIs")
> Fixes: a46349227cd8 ("libbpf: Add linker extern resolution support for functions and global variables")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> 
> [...]

Here is the summary with links:
  - [bpf-next] libbpf: fix hypothetical STT_SECTION extern NULL deref case
    https://git.kernel.org/bpf/bpf-next/c/e0525cd72b59

You are awesome, thank you!
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