In attach_kprobe(), the parsing logic uses sscanf() to extract the target function name and offset from the section definition. Currently, if a user specifies a negative offset (e.g., SEC("kprobe/func+-100")), the input is not explicitly caught and reported as an error. This commit updates the logic to explicitly notify the user when a negative integer is provided. To facilitate this check, the offset variable is changed from unsigned long to long so that sscanf() can accurately capture a negative input for evaluation. If a negative offset is detected, the loader will now print an informative warning stating that the offset must be non-negative, and return -EINVAL. Additionally, free(func) is called in this new error path to prevent a memory leak, as the function name string is dynamically allocated by sscanf(). Fixes: e3f9bc35ea7e9 ("libbpf: Allow decimal offset for kprobes") Acked-by: Mykyta Yatsenko Signed-off-by: Aaron Tomlin --- Changes in v2 [1]: - Corrected subject prefix to target "bpf-next" (Mykyta Yatsenko) - Added "Fixes:" tag (Mykyta Yatsenko) - Added "Acked-by:" tag from Mykyta Yatsenko Changes in v1 [2]: - Added omitted mailing list entries [1]: https://lore.kernel.org/lkml/20260417195816.1265179-1-atomlin@atomlin.com/ [2]: https://lore.kernel.org/bpf/0a8afc43-dfd8-4aa0-ae94-a82f8c307599@gmail.com/T/#t tools/lib/bpf/libbpf.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 8b0c3246097f..af81e0e200b9 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -12279,7 +12279,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link) { DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts); - unsigned long offset = 0; + long offset = 0; const char *func_name; char *func; int n; @@ -12301,6 +12301,13 @@ static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf pr_warn("kprobe name is invalid: %s\n", func_name); return -EINVAL; } + + if (offset < 0) { + free(func); + pr_warn("kprobe offset must be a non-negative integer: %li\n", offset); + return -EINVAL; + } + if (opts.retprobe && offset != 0) { free(func); pr_warn("kretprobes do not support offset specification\n"); -- 2.51.0