[PATCH bpf-next v2] libbpf: Fix program log buffer size validation

[Luis Vieira]

bpf_program__set_log_buf() checks the existing prog->log_size instead
of the incoming log_size argument when enforcing the UINT_MAX limit.
As a result, an oversized value can be accepted.

The setter also accepts a non-NULL log_buf with a zero log_size, while
bpf_prog_load() rejects mismatched log buffer and size values.

Validate the log buffer and size pair consistently with bpf_prog_load(),
and check the supplied log_size against UINT_MAX.

Signed-off-by: Luis Vieira <luisflavieira@xxxxxxxxx>
---
Changes in v2:
- Target bpf-next instead of bpf and drop the Fixes tag.
- Drop the regression selftest.
- Validate log_buf and log_size consistently with bpf_prog_load().
- Link to v1: https://patch.msgid.link/20260914-libbpf-log-buf-fix-v1-1-f592caffcc71@xxxxxxxxx

To: Andrii Nakryiko <andrii@xxxxxxxxxx>
To: Eduard Zingerman <eddyz87@xxxxxxxxx>
To: Ihor Solodrai <ihor.solodrai@xxxxxxxxx>
To: Alexei Starovoitov <ast@xxxxxxxxxx>
To: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
To: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
To: Martin KaFai Lau <martin.lau@xxxxxxxxx>
To: Song Liu <song@xxxxxxxxxx>
To: Yonghong Song <yonghong.song@xxxxxxxxx>
To: Jiri Olsa <jolsa@xxxxxxxxxx>
To: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 tools/lib/bpf/libbpf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 613afae26519..f7a0517d8fa8 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9966,9 +9966,9 @@ const char *bpf_program__log_buf(const struct bpf_program *prog, size_t *log_siz
 
 int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log_size)
 {
-	if (log_size && !log_buf)
+	if (!!log_buf != !!log_size)
 		return libbpf_err(-EINVAL);
-	if (prog->log_size > UINT_MAX)
+	if (log_size > UINT_MAX)
 		return libbpf_err(-EINVAL);
 	if (prog->obj->state >= OBJ_LOADED)
 		return libbpf_err(-EBUSY);

---
base-commit: 5ef40d69b38a93bc9951dadb1a15c85c597e1a40
change-id: 20260913-libbpf-log-buf-fix-49f5038caa5d

Best regards,
--  
Luis Vieira <luisflavieira@xxxxxxxxx>