bpf, mprog: Fix maximum program check on mprog attachment

After Paul's recent improvement to syzkaller to improve coverage for
bpf_mprog and tcx, it hit a splat that the program limit was surpassed.
What happened is that the maximum number of progs got added, followed
by another prog add request which adds with BPF_F_BEFORE flag relative
to the last program in the array. The idx >= bpf_mprog_max() check in
bpf_mprog_attach() still passes because the index is below the maximum
but the maximum will be surpassed. We need to add a check upfront for
insertions to catch this situation.

Fixes: 053c8e1f235d ("bpf: Add generic attach/detach/query API for multi-progs")
Reported-by: syzbot+baa44e3dbbe48e05c1ad@syzkaller.appspotmail.com
Reported-by: syzbot+b97d20ed568ce0951a06@syzkaller.appspotmail.com
Reported-by: syzbot+2558ca3567a77b7af4e3@syzkaller.appspotmail.com
Co-developed-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: syzbot+baa44e3dbbe48e05c1ad@syzkaller.appspotmail.com
Tested-by: syzbot+b97d20ed568ce0951a06@syzkaller.appspotmail.com
Link: https://github.com/google/syzkaller/pull/4207
Link: https://lore.kernel.org/bpf/20230929204121.20305-1-daniel@iogearbox.net

diff --git a/kernel/bpf/mprog.c b/kernel/bpf/mprog.c
index 32d2c48..007d98c 100644 (file)
--- a/kernel/bpf/mprog.c
+++ b/kernel/bpf/mprog.c
@@ -253,6 +253,9 @@ int bpf_mprog_attach(struct bpf_mprog_entry *entry,
                        goto out;
                }
                idx = tidx;
+       } else if (bpf_mprog_total(entry) == bpf_mprog_max()) {
+               ret = -ERANGE;
+               goto out;
        }
        if (flags & BPF_F_BEFORE) {
                tidx = bpf_mprog_pos_before(entry, &rtuple);