On 30 Apr 2020, at 20:12, Andrii Nakryiko wrote:
On Thu, Apr 30, 2020 at 3:24 AM Eelco Chaudron <echaudro@xxxxxxxxxx>
wrote:
When the probe code was failing for any reason ENOTSUP was returned,
even
if this was due to no having enough lock space. This patch fixes this
by
returning EPERM to the user application, so it can respond and
increase
the RLIMIT_MEMLOCK size.
Signed-off-by: Eelco Chaudron <echaudro@xxxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8f480e29a6b0..a62388a151d4 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3381,8 +3381,13 @@ bpf_object__probe_caps(struct bpf_object *obj)
for (i = 0; i < ARRAY_SIZE(probe_fn); i++) {
ret = probe_fn[i](obj);
- if (ret < 0)
+ if (ret < 0) {
pr_debug("Probe #%d failed with %d.\n", i,
ret);
+ if (ret == -EPERM) {
+ pr_perm_msg(ret);
+ return ret;
I think this is dangerous to do. This detection loop is not supposed
to return error to user if any of the features are missing. I'd feel
more comfortable if we split bpf_object__probe_name() into two tests:
one testing trivial program and another testing same program with
name. If the first one fails with EPERM -- then we can return error to
user. If anything else fails -- that's ok. Thoughts?
Before sending the patch I briefly checked the existing probes and did
not see any other code path that could lead to EPERM. But you are right
that this might not be the case for previous kernels. So you suggest
something like this?
diff --git a/src/libbpf.c b/src/libbpf.c
index ff91742..fd5fdee 100644
--- a/src/libbpf.c
+++ b/src/libbpf.c
@@ -3130,7 +3130,7 @@ int bpf_map__resize(struct bpf_map *map, __u32
max_entries)
}
static int
-bpf_object__probe_name(struct bpf_object *obj)
+bpf_object__probe_loading(struct bpf_object *obj)
{
struct bpf_load_program_attr attr;
char *cp, errmsg[STRERR_BUFSIZE];
@@ -3157,8 +3157,26 @@ bpf_object__probe_name(struct bpf_object *obj)
}
close(ret);
- /* now try the same program, but with the name */
+ return 0;
+}
+static int
+bpf_object__probe_name(struct bpf_object *obj)
+{
+ struct bpf_load_program_attr attr;
+ struct bpf_insn insns[] = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ };
+ int ret;
+
+ /* make sure loading with name works */
+
+ memset(&attr, 0, sizeof(attr));
+ attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
+ attr.insns = insns;
+ attr.insns_cnt = ARRAY_SIZE(insns);
+ attr.license = "GPL";
attr.name = "test";
ret = bpf_load_program_xattr(&attr, NULL, 0);
if (ret >= 0) {
@@ -3328,6 +3346,11 @@ bpf_object__probe_caps(struct bpf_object *obj)
};
int i, ret;
+ if (bpf_object__probe_loading(obj) == -EPERM) {
+ pr_perm_msg(-EPERM);
+ return -EPERM;
+ }
+
for (i = 0; i < ARRAY_SIZE(probe_fn); i++) {
ret = probe_fn[i](obj);
if (ret < 0)
Let me know, and I sent out a v2.
Cheers,
Eelco
