From: Lorenz Bauer <lmb@cloudflare.com>
To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org
Cc: kernel-team@cloudflare.com, netdev@vger.kernel.org,
bpf@vger.kernel.org, Lorenz Bauer <lmb@cloudflare.com>
Subject: [PATCH bpf v2 1/2] bpf: link: refuse non-O_RDWR flags in BPF_OBJ_GET
Date: Fri, 26 Mar 2021 16:05:00 +0000 [thread overview]
Message-ID: <20210326160501.46234-1-lmb@cloudflare.com> (raw)
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>
---
kernel/bpf/inode.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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;
--
2.27.0
next reply other threads:[~2021-03-26 16:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-26 16:05 Lorenz Bauer [this message]
2021-03-26 16:05 ` [PATCH bpf v2 2/2] bpf: program: refuse non-O_RDWR flags in BPF_OBJ_GET Lorenz Bauer
2021-03-26 20:13 ` Song Liu
2021-03-28 4:51 ` Andrii Nakryiko
2021-03-29 8:19 ` Lorenz Bauer
2021-03-28 4:49 ` [PATCH bpf v2 1/2] bpf: link: " Andrii Nakryiko
2021-03-31 14:04 ` Lorenz Bauer
2021-04-01 18:04 ` Alexei Starovoitov
2021-04-01 21:44 ` Alexei Starovoitov
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