netdev - [PATCH 1/1] [bpf-next] libbpf: fix off-by-one error for BPF_LOG_BUF

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Date:   Fri, 19 Apr 2019 09:55:52 -0500
From:   "McCabe, Robert J" <Robert.McCabe@...kwellcollins.com>
To:     netdev@...r.kernel.org
Cc:     robert.mccabe@...kwellcollins.com
Subject: [PATCH 1/1] [bpf-next] libbpf: fix off-by-one error for BPF_LOG_BUF_SIZE

The BPF_PROG_LOAD condition for kernel version <= 5.1 is

   log->len_total > UINT_MAX >> 8 /* (16 * 1024 * 1024) - 1 */

Signed-off-by: McCabe, Robert J <Robert.McCabe@...kwellcollins.com>
---
 tools/lib/bpf/bpf.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index bc30783d1403..62d67caa7aea 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -92,7 +92,7 @@ struct bpf_load_program_attr {
 #define MAPS_RELAX_COMPAT	0x01

 /* Recommend log buffer size */
-#define BPF_LOG_BUF_SIZE (16 * 1024 * 1024) /* verifier maximum in kernels <= 5.1 */
+#define BPF_LOG_BUF_SIZE ((16 * 1024 * 1024) - 1) /* verifier maximum in kernels <= 5.1 */
 LIBBPF_API int
 bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 		       char *log_buf, size_t log_buf_sz);
--
2.17.1