From be70bcd53de66e86f2726e576307cbdaebd3b1a5 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Tue, 9 Apr 2019 23:20:04 +0200 Subject: bpf: do not retain flags that are not tied to map lifetime Both BPF_F_WRONLY / BPF_F_RDONLY flags are tied to the map file descriptor, but not to the map object itself! Meaning, at map creation time BPF_F_RDONLY can be set to make the map read-only from syscall side, but this holds only for the returned fd, so any other fd either retrieved via bpf file system or via map id for the very same underlying map object can have read-write access instead. Given that, keeping the two flags around in the map_flags attribute and exposing them to user space upon map dump is misleading and may lead to false conclusions. Since these two flags are not tied to the map object lets also not store them as map property. Signed-off-by: Daniel Borkmann Acked-by: Martin KaFai Lau Signed-off-by: Alexei Starovoitov --- kernel/bpf/syscall.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'kernel/bpf') diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 828518bb947b..56b4b0e08b3b 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -166,13 +166,25 @@ void bpf_map_area_free(void *area) kvfree(area); } +static u32 bpf_map_flags_retain_permanent(u32 flags) +{ + /* Some map creation flags are not tied to the map object but + * rather to the map fd instead, so they have no meaning upon + * map object inspection since multiple file descriptors with + * different (access) properties can exist here. Thus, given + * this has zero meaning for the map itself, lets clear these + * from here. + */ + return flags & ~(BPF_F_RDONLY | BPF_F_WRONLY); +} + void bpf_map_init_from_attr(struct bpf_map *map, union bpf_attr *attr) { map->map_type = attr->map_type; map->key_size = attr->key_size; map->value_size = attr->value_size; map->max_entries = attr->max_entries; - map->map_flags = attr->map_flags; + map->map_flags = bpf_map_flags_retain_permanent(attr->map_flags); map->numa_node = bpf_map_attr_numa_node(attr); } -- cgit v1.2.3