* [PATCH bpf-next] libbpf: fix crash in XDP socket part with new larger BPF_LOG_BUF_SIZE
@ 2019-04-09 12:49 Magnus Karlsson
2019-04-09 16:04 ` Jonathan Lemon
2019-04-09 21:44 ` Daniel Borkmann
0 siblings, 2 replies; 3+ messages in thread
From: Magnus Karlsson @ 2019-04-09 12:49 UTC (permalink / raw)
To: magnus.karlsson, bjorn.topel, ast, daniel, netdev, bpf
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 to allocate the
log_buf using malloc instead. If the allocation fails, we go ahead and
load the program without a log buffer.
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
---
tools/lib/bpf/xsk.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 8d0078b..412531b 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -259,7 +259,7 @@ 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];
+ char *bpf_log_buf;
int err, prog_fd;
/* This is the C-program:
@@ -307,22 +307,27 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk)
};
size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);
+ bpf_log_buf = malloc(BPF_LOG_BUF_SIZE);
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);
+ bpf_log_buf ? BPF_LOG_BUF_SIZE : 0);
if (prog_fd < 0) {
- pr_warning("BPF log buffer:\n%s", bpf_log_buf);
- return prog_fd;
+ if (bpf_log_buf)
+ pr_warning("BPF log buffer:\n%s", bpf_log_buf);
+ err = prog_fd;
+ goto out;
}
err = bpf_set_link_xdp_fd(xsk->ifindex, prog_fd, xsk->config.xdp_flags);
if (err) {
close(prog_fd);
- return err;
+ goto out;
}
xsk->prog_fd = prog_fd;
- return 0;
+out:
+ free(bpf_log_buf);
+ return err;
}
static int xsk_get_max_queues(struct xsk_socket *xsk)
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH bpf-next] libbpf: fix crash in XDP socket part with new larger BPF_LOG_BUF_SIZE
2019-04-09 12:49 [PATCH bpf-next] libbpf: fix crash in XDP socket part with new larger BPF_LOG_BUF_SIZE Magnus Karlsson
@ 2019-04-09 16:04 ` Jonathan Lemon
2019-04-09 21:44 ` Daniel Borkmann
1 sibling, 0 replies; 3+ messages in thread
From: Jonathan Lemon @ 2019-04-09 16:04 UTC (permalink / raw)
To: Magnus Karlsson; +Cc: bjorn.topel, ast, daniel, netdev, bpf
On 9 Apr 2019, at 5:49, Magnus Karlsson wrote:
> 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 to allocate the
> log_buf using malloc instead. If the allocation fails, we go ahead and
> load the program without a log buffer.
>
> Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH bpf-next] libbpf: fix crash in XDP socket part with new larger BPF_LOG_BUF_SIZE
2019-04-09 12:49 [PATCH bpf-next] libbpf: fix crash in XDP socket part with new larger BPF_LOG_BUF_SIZE Magnus Karlsson
2019-04-09 16:04 ` Jonathan Lemon
@ 2019-04-09 21:44 ` Daniel Borkmann
1 sibling, 0 replies; 3+ messages in thread
From: Daniel Borkmann @ 2019-04-09 21:44 UTC (permalink / raw)
To: Magnus Karlsson, bjorn.topel, ast, netdev, bpf
On 04/09/2019 02:49 PM, Magnus Karlsson wrote:
> 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 to allocate the
> log_buf using malloc instead. If the allocation fails, we go ahead and
> load the program without a log buffer.
>
> Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
For these few 17 insn, wouldn't it make more sense to rather shrink the
log buffer size? malloc'ing 16M seems like overkill for the tiny program.
I don't think there is a specific need to stick with BPF_LOG_BUF_SIZE.
Why not simplifying it like the following where we also don't need to
cope will allocation failure, for example:
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;
}
Thanks,
Daniel
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2019-04-09 12:49 [PATCH bpf-next] libbpf: fix crash in XDP socket part with new larger BPF_LOG_BUF_SIZE Magnus Karlsson
2019-04-09 16:04 ` Jonathan Lemon
2019-04-09 21:44 ` Daniel Borkmann
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