bpf: write back the verifier log buffer as it gets filled

Verifier log buffer can be quite large (up to 16MB currently).
As Eric Dumazet points out if we allow multiple verification
requests to proceed simultaneously, malicious user may use the
verifier as a way of allocating large amounts of unswappable
memory to OOM the host.

Switch to a strategy of allocating a smaller buffer (1024B)
and writing it out into the user buffer after every print.

While at it remove the old BUG_ON().

This is in preparation of the global verifier lock removal.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 5ddb9a626a51e2b8ac06ebdb7eb59ce0c25a7750..f00ef751c1c5290c0c62a04bcfb9dcc6d4ae606c 100644 (file)
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -115,9 +115,11 @@ struct bpf_insn_aux_data {
 
 #define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
 
+#define BPF_VERIFIER_TMP_LOG_SIZE      1024
+
 struct bpf_verifer_log {
        u32 level;
-       char *kbuf;
+       char kbuf[BPF_VERIFIER_TMP_LOG_SIZE];
        char __user *ubuf;
        u32 len_used;
        u32 len_total;

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 274c6582ec398910754a6fe18936b628dea3f488..2cdbcc4f8f6b274ff3ca92de4b77c1955899cd17 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -165,15 +165,26 @@ static __printf(2, 3) void verbose(struct bpf_verifier_env *env,
                                   const char *fmt, ...)
 {
        struct bpf_verifer_log *log = &env->log;
+       unsigned int n;
        va_list args;
 
-       if (!log->level || bpf_verifier_log_full(log))
+       if (!log->level || !log->ubuf || bpf_verifier_log_full(log))
                return;
 
        va_start(args, fmt);
-       log->len_used += vscnprintf(log->kbuf + log->len_used,
-                                   log->len_total - log->len_used, fmt, args);
+       n = vscnprintf(log->kbuf, BPF_VERIFIER_TMP_LOG_SIZE, fmt, args);
        va_end(args);
+
+       WARN_ONCE(n >= BPF_VERIFIER_TMP_LOG_SIZE - 1,
+                 "verifier log line truncated - local buffer too short\n");
+
+       n = min(log->len_total - log->len_used - 1, n);
+       log->kbuf[n] = '\0';
+
+       if (!copy_to_user(log->ubuf + log->len_used, log->kbuf, n + 1))
+               log->len_used += n;
+       else
+               log->ubuf = NULL;
 }
 
 static bool type_is_pkt_pointer(enum bpf_reg_type type)
@@ -4263,11 +4274,6 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
                if (log->len_total < 128 || log->len_total > UINT_MAX >> 8 ||
                    !log->level || !log->ubuf)
                        goto err_unlock;
-
-               ret = -ENOMEM;
-               log->kbuf = vmalloc(log->len_total);
-               if (!log->kbuf)
-                       goto err_unlock;
        }
 
        env->strict_alignment = !!(attr->prog_flags & BPF_F_STRICT_ALIGNMENT);
@@ -4304,18 +4310,11 @@ skip_full_check:
        if (ret == 0)
                ret = fixup_bpf_calls(env);
 
-       if (log->level && bpf_verifier_log_full(log)) {
-               BUG_ON(log->len_used >= log->len_total);
-               /* verifier log exceeded user supplied buffer */
+       if (log->level && bpf_verifier_log_full(log))
                ret = -ENOSPC;
-               /* fall through to return what was recorded */
-       }
-
-       /* copy verifier log back to user space including trailing zero */
-       if (log->level && copy_to_user(log->ubuf, log->kbuf,
-                                      log->len_used + 1) != 0) {
+       if (log->level && !log->ubuf) {
                ret = -EFAULT;
-               goto free_log_buf;
+               goto err_release_maps;
        }
 
        if (ret == 0 && env->used_map_cnt) {
@@ -4326,7 +4325,7 @@ skip_full_check:
 
                if (!env->prog->aux->used_maps) {
                        ret = -ENOMEM;
-                       goto free_log_buf;
+                       goto err_release_maps;
                }
 
                memcpy(env->prog->aux->used_maps, env->used_maps,
@@ -4339,9 +4338,7 @@ skip_full_check:
                convert_pseudo_ld_imm64(env);
        }
 
-free_log_buf:
-       if (log->level)
-               vfree(log->kbuf);
+err_release_maps:
        if (!env->prog->aux->used_maps)
                /* if we didn't copy map pointers into bpf_prog_info, release
                 * them now. Otherwise free_bpf_prog_info() will release them.