Re: [PATCH bpf v2 2/2] bpf: program: refuse non-O_RDWR flags in BPF_OBJ_GET

On Fri, 26 Mar 2021 at 20:14, Song Liu [off-list ref] wrote:

On Fri, Mar 26, 2021 at 9:07 AM Lorenz Bauer [off-list ref] wrote:

quoted

As for bpf_link, refuse creating a non-O_RDWR fd. Since program fds
currently don't allow modifications this is a precaution, not a
straight up bug fix.

Signed-off-by: Lorenz Bauer <redacted>
---
 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 dc56237d6960..d2de2abec35b 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c

@@ -543,7 +543,7 @@ int bpf_obj_get_user(const char __user *pathname, int flags)
                return PTR_ERR(raw);

For both patches, shall we do the check before bpf_obj_do_get(), which is a few
lines above?

type is filled in by bpf_obj_do_get, so we can't avoid calling it. As
Andrii mentions we need to allow flags for map.

Thanks,
Song

quoted

        if (type == BPF_TYPE_PROG)
-               ret = bpf_prog_new_fd(raw);
+               ret = (f_flags != O_RDWR) ? -EINVAL : bpf_prog_new_fd(raw);
        else if (type == BPF_TYPE_MAP)
                ret = bpf_map_new_fd(raw, f_flags);
        else if (type == BPF_TYPE_LINK)
--
2.27.0

-- 
Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK

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