This is a note to let you know that I've just added the patch titled bpf: link: Refuse non-O_RDWR flags in BPF_OBJ_GET to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bpf-link-refuse-non-o_rdwr-flags-in-bpf_obj_get.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 25fc94b2f02d832fa8e29419699dcc20b0b05c6a Mon Sep 17 00:00:00 2001 From: Lorenz Bauer <lmb@xxxxxxxxxxxxxx> Date: Fri, 26 Mar 2021 16:05:00 +0000 Subject: bpf: link: Refuse non-O_RDWR flags in BPF_OBJ_GET From: Lorenz Bauer <lmb@xxxxxxxxxxxxxx> commit 25fc94b2f02d832fa8e29419699dcc20b0b05c6a upstream. 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@xxxxxxxxxxxxxx> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Link: https://lore.kernel.org/bpf/20210326160501.46234-1-lmb@xxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/bpf/inode.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/bpf/inode.c +++ b/kernel/bpf/inode.c @@ -546,7 +546,7 @@ int bpf_obj_get_user(const char __user * 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; Patches currently in stable-queue which might be from lmb@xxxxxxxxxxxxxx are queue-5.11/bpf-link-refuse-non-o_rdwr-flags-in-bpf_obj_get.patch queue-5.11/bpf-sockmap-fix-sk-prot-unhash-op-reset.patch