From 6c6b4146deb12d20f42490d5013f2043df942161 Mon Sep 17 00:00:00 2001 From: Yureka Lilian Date: Thu, 14 Aug 2025 20:01:12 +0200 Subject: [PATCH 1/2] libbpf: Fix reuse of DEVMAP Previously, re-using pinned DEVMAP maps would always fail, because get_map_info on a DEVMAP always returns flags with BPF_F_RDONLY_PROG set, but BPF_F_RDONLY_PROG being set on a map during creation is invalid. Thus, ignore the BPF_F_RDONLY_PROG flag in the flags returned from get_map_info when checking for compatibility with an existing DEVMAP. The same problem is handled in a third-party ebpf library: - https://github.com/cilium/ebpf/issues/925 - https://github.com/cilium/ebpf/pull/930 Fixes: 0cdbb4b09a06 ("devmap: Allow map lookups from eBPF") Signed-off-by: Yureka Lilian Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250814180113.1245565-3-yuka@yuka.dev --- tools/lib/bpf/libbpf.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 8f5a81b672e1..fe4fc5438678 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -5093,6 +5093,16 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd) return false; } + /* + * bpf_get_map_info_by_fd() for DEVMAP will always return flags with + * BPF_F_RDONLY_PROG set, but it generally is not set at map creation time. + * Thus, ignore the BPF_F_RDONLY_PROG flag in the flags returned from + * bpf_get_map_info_by_fd() when checking for compatibility with an + * existing DEVMAP. + */ + if (map->def.type == BPF_MAP_TYPE_DEVMAP || map->def.type == BPF_MAP_TYPE_DEVMAP_HASH) + map_info.map_flags &= ~BPF_F_RDONLY_PROG; + return (map_info.type == map->def.type && map_info.key_size == map->def.key_size && map_info.value_size == map->def.value_size && From 7f8fa9d370c11ba2fb296598267e14d3bfe4ea11 Mon Sep 17 00:00:00 2001 From: Yureka Lilian Date: Thu, 14 Aug 2025 20:01:13 +0200 Subject: [PATCH 2/2] selftests/bpf: Add test for DEVMAP reuse The test covers basic re-use of a pinned DEVMAP map, with both matching and mismatching parameters. Signed-off-by: Yureka Lilian Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20250814180113.1245565-4-yuka@yuka.dev --- .../bpf/prog_tests/pinning_devmap_reuse.c | 50 +++++++++++++++++++ .../selftests/bpf/progs/test_pinning_devmap.c | 20 ++++++++ 2 files changed, 70 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/pinning_devmap_reuse.c create mode 100644 tools/testing/selftests/bpf/progs/test_pinning_devmap.c diff --git a/tools/testing/selftests/bpf/prog_tests/pinning_devmap_reuse.c b/tools/testing/selftests/bpf/prog_tests/pinning_devmap_reuse.c new file mode 100644 index 000000000000..9ae49b587f3e --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/pinning_devmap_reuse.c @@ -0,0 +1,50 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include +#include + + +#include "test_pinning_devmap.skel.h" + +void test_pinning_devmap_reuse(void) +{ + const char *pinpath1 = "/sys/fs/bpf/pinmap1"; + const char *pinpath2 = "/sys/fs/bpf/pinmap2"; + struct test_pinning_devmap *skel1 = NULL, *skel2 = NULL; + int err; + DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts); + + /* load the object a first time */ + skel1 = test_pinning_devmap__open_and_load(); + if (!ASSERT_OK_PTR(skel1, "skel_load1")) + goto out; + + /* load the object a second time, re-using the pinned map */ + skel2 = test_pinning_devmap__open_and_load(); + if (!ASSERT_OK_PTR(skel2, "skel_load2")) + goto out; + + /* we can close the reference safely without + * the map's refcount falling to 0 + */ + test_pinning_devmap__destroy(skel1); + skel1 = NULL; + + /* now, swap the pins */ + err = renameat2(0, pinpath1, 0, pinpath2, RENAME_EXCHANGE); + if (!ASSERT_OK(err, "swap pins")) + goto out; + + /* load the object again, this time the re-use should fail */ + skel1 = test_pinning_devmap__open_and_load(); + if (!ASSERT_ERR_PTR(skel1, "skel_load3")) + goto out; + +out: + unlink(pinpath1); + unlink(pinpath2); + test_pinning_devmap__destroy(skel1); + test_pinning_devmap__destroy(skel2); +} diff --git a/tools/testing/selftests/bpf/progs/test_pinning_devmap.c b/tools/testing/selftests/bpf/progs/test_pinning_devmap.c new file mode 100644 index 000000000000..c855f8f87eff --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_pinning_devmap.c @@ -0,0 +1,20 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include + +struct { + __uint(type, BPF_MAP_TYPE_DEVMAP); + __uint(max_entries, 1); + __type(key, __u32); + __type(value, __u32); + __uint(pinning, LIBBPF_PIN_BY_NAME); +} pinmap1 SEC(".maps"); + +struct { + __uint(type, BPF_MAP_TYPE_DEVMAP); + __uint(max_entries, 2); + __type(key, __u32); + __type(value, __u32); + __uint(pinning, LIBBPF_PIN_BY_NAME); +} pinmap2 SEC(".maps");