From: Yuan Chen show_kprobe_multi_{plain,json}() walk the sorted kallsyms array against the sorted addr/cookie array with j as a cursor into the latter. The loop terminating condition is checked after the cursor has already been used to access the array: if (j++ == info->kprobe_multi.count) break; After all count entries have been printed, j has been bumped to count, but the loop keeps running and dereferences data[count] -- one element past the end of the calloc(count, sizeof(*data)) allocation -- while comparing every remaining kallsyms symbol. If the out-of-bounds value happens to match a symbol address, a bogus entry with a garbage addr/cookie pair is printed to boot. Fix the off-by-one by advancing the cursor before the comparison, so the loop terminates as soon as the last entry has been printed. Verified with an ASAN build of bpftool against a live kprobe_multi link of 3 symbols: before: ERROR: AddressSanitizer: heap-buffer-overflow READ of size 8 at link.c:860 (show_kprobe_multi_plain) and link.c:352 (show_kprobe_multi_json), 0 bytes after the 48-byte get_addr_cookie_array() allocation after: clean output, no ASAN report Fixes: edd7f49bb884 ("bpftool: Show kprobe_multi link info") Signed-off-by: Yuan Chen --- tools/bpf/bpftool/link.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c index 088d1d206065..5cffa2d283b4 100644 --- a/tools/bpf/bpftool/link.c +++ b/tools/bpf/bpftool/link.c @@ -364,7 +364,7 @@ show_kprobe_multi_json(struct bpf_link_info *info, json_writer_t *wtr) } jsonw_uint_field(json_wtr, "cookie", data[j].cookie); jsonw_end_object(json_wtr); - if (j++ == info->kprobe_multi.count) + if (++j == info->kprobe_multi.count) break; } jsonw_end_array(json_wtr); @@ -867,7 +867,7 @@ static void show_kprobe_multi_plain(struct bpf_link_info *info) else printf(" "); - if (j++ == info->kprobe_multi.count) + if (++j == info->kprobe_multi.count) break; } error: -- 2.54.0