FAILED: patch "[PATCH] bpf: Resolve to prog->aux->dst_prog->type only for" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4a9c7bbe2ed4d2b240674b1fb606c41d3940c412 Mon Sep 17 00:00:00 2001
From: Martin KaFai Lau <[email protected]>
Date: Tue, 29 Mar 2022 18:14:56 -0700
Subject: [PATCH] bpf: Resolve to prog->aux->dst_prog->type only for
BPF_PROG_TYPE_EXT

The commit 7e40781cc8b7 ("bpf: verifier: Use target program's type for access verifications") fixes the verifier checking for BPF_PROG_TYPE_EXT (extension)
prog such that the verifier looks for things based
on the target prog type that it is extending instead of
the BPF_PROG_TYPE_EXT itself.

The current resolve_prog_type() returns the target prog type. It checks for nullness on prog->aux->dst_prog. However, when loading a BPF_PROG_TYPE_TRACING prog and it is tracing another bpf prog instead of a kernel function, prog->aux->dst_prog is not NULL also. In this case, the verifier should still verify as the BPF_PROG_TYPE_TRACING type instead of the traced prog type in prog->aux->dst_prog->type.

An oops has been reported when tracing a struct_ops prog. A NULL dereference happened in check_return_code() when accessing the prog->aux->attach_func_proto->type and prog->aux->attach_func_proto is NULL here because the traced struct_ops prog has the "unreliable" set.

This patch is to change the resolve_prog_type() to only return the target prog type if the prog being verified is BPF_PROG_TYPE_EXT.

index c1fc4af47f69..3a9d2d7cc6b7 100644
@@ -570,9 +570,11 @@ static inline u32 type_flag(u32 type)
 	return type & ~BPF_BASE_TYPE_MASK;
 }
 
+/* only use after check_attach_btf_id() */
 static inline enum bpf_prog_type resolve_prog_type(struct bpf_prog *prog)
 {
-	return prog->aux->dst_prog ? prog->aux->dst_prog->type : prog->type;
+	return prog->type == BPF_PROG_TYPE_EXT ?
+		prog->aux->dst_prog->type : prog->type;
 }
 
 #endif /* _LINUX_BPF_VERIFIER_H */