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

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Commit 06744f2469 ("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: 06744f2469 ("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>
This commit is contained in:
Jinghao Jia
2023-09-17 16:42:20 -05:00
committed by Alexei Starovoitov
parent 0ee352fe0d
commit 9220c3ef6f
1 changed files with 20 additions and 3 deletions
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23
samples/bpf/syscall_tp_user.c
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@@ -48,7 +48,7 @@ static void verify_map(int map_id)
static int test(char *filename, int nr_tests) static int test(char *filename, int nr_tests)
{ {
int map0_fds[nr_tests], map1_fds[nr_tests], fd, i, j = 0; 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_object *objs[nr_tests];
struct bpf_program *prog; struct bpf_program *prog;
@@ -60,6 +60,19 @@ static int test(char *filename, int nr_tests)
goto cleanup; 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 */ /* load BPF program */
if (bpf_object__load(objs[i])) { if (bpf_object__load(objs[i])) {
fprintf(stderr, "loading BPF object file failed\n"); fprintf(stderr, "loading BPF object file failed\n");
@@ -107,8 +120,12 @@ static int test(char *filename, int nr_tests)
} }
cleanup: cleanup:
for (j--; j >= 0; j--) if (links) {
bpf_link__destroy(links[j]); for (j--; j >= 0; j--)
bpf_link__destroy(links[j]);
free(links);
}
for (i--; i >= 0; i--) for (i--; i >= 0; i--)
bpf_object__close(objs[i]); bpf_object__close(objs[i]);