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[bpf-next,v9,01/11] bpf: disallow attaching modify_return tracing functions to other BPF programs

Message ID 160106910067.27725.5163435783598211744.stgit@toke.dk (mailing list archive)
State Superseded
Headers show
Series bpf: Support multi-attach for freplace programs | expand

Commit Message

Toke Høiland-Jørgensen Sept. 25, 2020, 9:25 p.m. UTC
From: Toke Høiland-Jørgensen <toke@redhat.com>

From the checks and commit messages for modify_return, it seems it was
never the intention that it should be possible to attach a tracing program
with expected_attach_type == BPF_MODIFY_RETURN to another BPF program.
However, check_attach_modify_return() will only look at the function name,
so if the target function starts with "security_", the attach will be
allowed even for bpf2bpf attachment.

Fix this oversight by also blocking the modification if a target program is

Fixes: 18644cec714a ("bpf: Fix use-after-free in fmod_ret check")
Fixes: 6ba43b761c41 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
 kernel/bpf/verifier.c |    5 +++++
 1 file changed, 5 insertions(+)
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diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 42dee5dcbc74..66b6714b3fd7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11470,6 +11470,11 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 				verbose(env, "%s is not sleepable\n",
 		} else if (prog->expected_attach_type == BPF_MODIFY_RETURN) {
+			if (tgt_prog) {
+				verbose(env, "can't modify return codes of BPF programs\n");
+				ret = -EINVAL;
+				goto out;
+			}
 			ret = check_attach_modify_return(prog, addr);
 			if (ret)
 				verbose(env, "%s() is not modifiable\n",