Revert "bpf: Prevent tail call between progs attached to different hooks"

This reverts commit 5d5e3b4 which is
commit 28ead3e upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Id8dbbec2cc722d014f33450af1f44801b26b6a8e
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: gregkh

include/linux/bpf.h

@@ -292,7 +292,6 @@ struct bpf_map {
 	 * same prog type, JITed flag and xdp_has_frags flag.
 	 */
 	struct {
-		const struct btf_type *attach_func_proto;
 		spinlock_t lock;
 		enum bpf_prog_type type;
 		bool jited;

kernel/bpf/core.c

@@ -2259,7 +2259,6 @@ bool bpf_prog_map_compatible(struct bpf_map *map,
 {
 	enum bpf_prog_type prog_type = resolve_prog_type(fp);
 	bool ret;
-	struct bpf_prog_aux *aux = fp->aux;
 
 	if (fp->kprobe_override)
 		return false;
@@ -2269,7 +2268,7 @@ bool bpf_prog_map_compatible(struct bpf_map *map,
 	 * in the case of devmap and cpumap). Until device checks
 	 * are implemented, prohibit adding dev-bound programs to program maps.
 	 */
-	if (bpf_prog_is_dev_bound(aux))
+	if (bpf_prog_is_dev_bound(fp->aux))
 		return false;
 
 	spin_lock(&map->owner.lock);
@@ -2279,26 +2278,12 @@ bool bpf_prog_map_compatible(struct bpf_map *map,
 		 */
 		map->owner.type  = prog_type;
 		map->owner.jited = fp->jited;
-		map->owner.xdp_has_frags = aux->xdp_has_frags;
-		map->owner.attach_func_proto = aux->attach_func_proto;
+		map->owner.xdp_has_frags = fp->aux->xdp_has_frags;
 		ret = true;
 	} else {
 		ret = map->owner.type  == prog_type &&
 		      map->owner.jited == fp->jited &&
-		      map->owner.xdp_has_frags == aux->xdp_has_frags;
-		if (ret &&
-		    map->owner.attach_func_proto != aux->attach_func_proto) {
-			switch (prog_type) {
-			case BPF_PROG_TYPE_TRACING:
-			case BPF_PROG_TYPE_LSM:
-			case BPF_PROG_TYPE_EXT:
-			case BPF_PROG_TYPE_STRUCT_OPS:
-				ret = false;
-				break;
-			default:
-				break;
-			}
-		}
+		      map->owner.xdp_has_frags == fp->aux->xdp_has_frags;
 	}
 	spin_unlock(&map->owner.lock);