From 9b6f4eb1570c219474f6029caea71584d7a2188a Mon Sep 17 00:00:00 2001
From: Anquan Wu <leiqi96@hotmail.com>
Date: Tue, 12 Jul 2022 11:15:40 +0800
Subject: [PATCH] libbpf: Fix the name of a reused map
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BPF map name is limited to BPF_OBJ_NAME_LEN.
A map name is defined as being longer than BPF_OBJ_NAME_LEN,
it will be truncated to BPF_OBJ_NAME_LEN when a userspace program
calls libbpf to create the map. A pinned map also generates a path
in the /sys. If the previous program wanted to reuse the map，
it can not get bpf_map by name, because the name of the map is only
partially the same as the name which get from pinned path.

The syscall information below show that map name "process_pinned_map"
is truncated to "process_pinned_".

    bpf(BPF_OBJ_GET, {pathname="/sys/fs/bpf/process_pinned_map",
    bpf_fd=0, file_flags=0}, 144) = -1 ENOENT (No such file or directory)

    bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_HASH, key_size=4,
    value_size=4,max_entries=1024, map_flags=0, inner_map_fd=0,
    map_name="process_pinned_",map_ifindex=0, btf_fd=3, btf_key_type_id=6,
    btf_value_type_id=10,btf_vmlinux_value_type_id=0}, 72) = 4

This patch check that if the name of pinned map are the same as the
actual name for the first (BPF_OBJ_NAME_LEN - 1),
bpf map still uses the name which is included in bpf object.

Fixes: 26736eb9a483 ("tools: libbpf: allow map reuse")
Signed-off-by: Anquan Wu <leiqi96@hotmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/OSZP286MB1725CEA1C95C5CB8E7CCC53FB8869@OSZP286MB1725.JPNP286.PROD.OUTLOOK.COM
---
 src/libbpf.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/libbpf.c b/src/libbpf.c
index 72548798..68da1aca 100644
--- a/src/libbpf.c
+++ b/src/libbpf.c
@@ -4327,7 +4327,7 @@ int bpf_map__set_autocreate(struct bpf_map *map, bool autocreate)
 int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 {
 	struct bpf_map_info info = {};
-	__u32 len = sizeof(info);
+	__u32 len = sizeof(info), name_len;
 	int new_fd, err;
 	char *new_name;
 
@@ -4337,7 +4337,12 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 	if (err)
 		return libbpf_err(err);
 
-	new_name = strdup(info.name);
+	name_len = strlen(info.name);
+	if (name_len == BPF_OBJ_NAME_LEN - 1 && strncmp(map->name, info.name, name_len) == 0)
+		new_name = strdup(map->name);
+	else
+		new_name = strdup(info.name);
+
 	if (!new_name)
 		return libbpf_err(-errno);