netdev - [PATCH bpf-next v2] libbpf: fix crash in XDP socket part with new larger BPF_LOG_BUF

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Message-Id: <1554879256-30587-1-git-send-email-magnus.karlsson@intel.com>
Date:   Wed, 10 Apr 2019 08:54:16 +0200
From:   Magnus Karlsson <magnus.karlsson@...el.com>
To:     magnus.karlsson@...el.com, bjorn.topel@...el.com, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH bpf-next v2] libbpf: fix crash in XDP socket part with new larger BPF_LOG_BUF_SIZE

In commit da11b417583e ("libbpf: teach libbpf about log_level bit 2"),
the BPF_LOG_BUF_SIZE was increased to 16M. The XDP socket part of
libbpf allocated the log_buf on the stack, but for the new 16M buffer
size this is not going to work. Change the code so it uses a 16K buffer
instead.

Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
---
v2: simplified code as suggested by Daniel Borkmann

 tools/lib/bpf/xsk.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 8d0078b..557ef8d 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -259,7 +259,8 @@ int xsk_umem__create(struct xsk_umem **umem_ptr, void *umem_area, __u64 size,

 static int xsk_load_xdp_prog(struct xsk_socket *xsk)
 {
-	char bpf_log_buf[BPF_LOG_BUF_SIZE];
+	static const int log_buf_size = 16 * 1024;
+	char log_buf[log_buf_size];
 	int err, prog_fd;

 	/* This is the C-program:
@@ -308,10 +309,10 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk)
 	size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);

 	prog_fd = bpf_load_program(BPF_PROG_TYPE_XDP, prog, insns_cnt,
-				   "LGPL-2.1 or BSD-2-Clause", 0, bpf_log_buf,
-				   BPF_LOG_BUF_SIZE);
+				   "LGPL-2.1 or BSD-2-Clause", 0, log_buf,
+				   log_buf_size);
 	if (prog_fd < 0) {
-		pr_warning("BPF log buffer:\n%s", bpf_log_buf);
+		pr_warning("BPF log buffer:\n%s", log_buf);
 		return prog_fd;
 	}

--
2.7.4