Commit 9220c3ef authored Sep 17, 2023 by Jinghao Jia Committed by Alexei Starovoitov Sep 21, 2023

samples/bpf: syscall_tp_user: Fix array out-of-bound access



Commit 06744f24 ("samples/bpf: Add openat2() enter/exit tracepoint
to syscall_tp sample") added two more eBPF programs to support the
openat2() syscall. However, it did not increase the size of the array
that holds the corresponding bpf_links. This leads to an out-of-bound
access on that array in the bpf_object__for_each_program loop and could
corrupt other variables on the stack. On our testing QEMU, it corrupts
the map1_fds array and causes the sample to fail:

  # ./syscall_tp
  prog #0: map ids 4 5
  verify map:4 val: 5
  map_lookup failed: Bad file descriptor

Dynamically allocate the array based on the number of programs reported
by libbpf to prevent similar inconsistencies in the future

Fixes: 06744f24 ("samples/bpf: Add openat2() enter/exit tracepoint to syscall_tp sample")
Signed-off-by: Jinghao Jia <jinghao@linux.ibm.com>
Signed-off-by: Ruowen Qin <ruowenq2@illinois.edu>
Signed-off-by: Jinghao Jia <jinghao7@illinois.edu>
Link: https://lore.kernel.org/r/20230917214220.637721-4-jinghao7@illinois.edu


Signed-off-by: Alexei Starovoitov <ast@kernel.org>

parent 0ee352fe

samples/bpf/syscall_tp_user.c

+20 −3

Original line number	Diff line number	Diff line
		@@ -48,7 +48,7 @@ static void verify_map(int map_id)
		static int test(char *filename, int nr_tests)
		{
		int map0_fds[nr_tests], map1_fds[nr_tests], fd, i, j = 0;
		struct bpf_link links[nr_tests 4];
		struct bpf_link **links = NULL;
		struct bpf_object *objs[nr_tests];
		struct bpf_program *prog;

		@@ -60,6 +60,19 @@ static int test(char *filename, int nr_tests)
		goto cleanup;
		}

		/* One-time initialization */
		if (!links) {
		int nr_progs = 0;

		bpf_object__for_each_program(prog, objs[i])
		nr_progs += 1;

		links = calloc(nr_progs * nr_tests, sizeof(struct bpf_link *));

		if (!links)
		goto cleanup;
		}

		/* load BPF program */
		if (bpf_object__load(objs[i])) {
		fprintf(stderr, "loading BPF object file failed\n");
		@@ -107,9 +120,13 @@ static int test(char *filename, int nr_tests)
		}

		cleanup:
		if (links) {
		for (j--; j >= 0; j--)
		bpf_link__destroy(links[j]);

		free(links);
		}

		for (i--; i >= 0; i--)
		bpf_object__close(objs[i]);
		return 0;