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authorLorenz Bauer <lmb@cloudflare.com>2021-03-26 19:05:00 +0300
committerAlexei Starovoitov <ast@kernel.org>2021-04-02 00:33:14 +0300
commit25fc94b2f02d832fa8e29419699dcc20b0b05c6a (patch)
tree666bd3bc5af6d37d7b02d639b06c9f7db8f984ce /kernel/bpf
parent06ab134ce8ecfa5a69e850f88f81c8a4c3fa91df (diff)
downloadlinux-25fc94b2f02d832fa8e29419699dcc20b0b05c6a.tar.xz
bpf: link: Refuse non-O_RDWR flags in BPF_OBJ_GET
Invoking BPF_OBJ_GET on a pinned bpf_link checks the path access permissions based on file_flags, but the returned fd ignores flags. This means that any user can acquire a "read-write" fd for a pinned link with mode 0664 by invoking BPF_OBJ_GET with BPF_F_RDONLY in file_flags. The fd can be used to invoke BPF_LINK_DETACH, etc. Fix this by refusing non-O_RDWR flags in BPF_OBJ_GET. This works because OBJ_GET by default returns a read write mapping and libbpf doesn't expose a way to override this behaviour for programs and links. Fixes: 70ed506c3bbc ("bpf: Introduce pinnable bpf_link abstraction") Signed-off-by: Lorenz Bauer <lmb@cloudflare.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Andrii Nakryiko <andrii@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20210326160501.46234-1-lmb@cloudflare.com
Diffstat (limited to 'kernel/bpf')
-rw-r--r--kernel/bpf/inode.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 1576ff331ee4..dc56237d6960 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -547,7 +547,7 @@ int bpf_obj_get_user(const char __user *pathname, int flags)
else if (type == BPF_TYPE_MAP)
ret = bpf_map_new_fd(raw, f_flags);
else if (type == BPF_TYPE_LINK)
- ret = bpf_link_new_fd(raw);
+ ret = (f_flags != O_RDWR) ? -EINVAL : bpf_link_new_fd(raw);
else
return -ENOENT;