Commit 108598c3 authored by Yafang Shao's avatar Yafang Shao Committed by Daniel Borkmann
Browse files

bpf: Fix memleak due to fentry attach failure 



If it fails to attach fentry, the allocated bpf trampoline image will be
left in the system. That can be verified by checking /proc/kallsyms.

This meamleak can be verified by a simple bpf program as follows:

  SEC("fentry/trap_init")
  int fentry_run()
  {
      return 0;
  }

It will fail to attach trap_init because this function is freed after
kernel init, and then we can find the trampoline image is left in the
system by checking /proc/kallsyms.

  $ tail /proc/kallsyms
  ffffffffc0613000 t bpf_trampoline_6442453466_1  [bpf]
  ffffffffc06c3000 t bpf_trampoline_6442453466_1  [bpf]

  $ bpftool btf dump file /sys/kernel/btf/vmlinux | grep "FUNC 'trap_init'"
  [2522] FUNC 'trap_init' type_id=119 linkage=static

  $ echo $((6442453466 & 0x7fffffff))
  2522

Note that there are two left bpf trampoline images, that is because the
libbpf will fallback to raw tracepoint if -EINVAL is returned.

Fixes: e21aa341 ("bpf: Fix fexit trampoline.")
Signed-off-by: default avatarYafang Shao <laoar.shao@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarSong Liu <song@kernel.org>
Cc: Jiri Olsa <olsajiri@gmail.com>
Link: https://lore.kernel.org/bpf/20230515130849.57502-2-laoar.shao@gmail.com
parent 47e79cbe

kernel/bpf/trampoline.c

+15 −6
Original line number Diff line number Diff line
@@ -251,11 +251,8 @@ bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_a 
	return tlinks;

}



static void __bpf_tramp_image_put_deferred(struct work_struct *work)

static void bpf_tramp_image_free(struct bpf_tramp_image *im)

{

	struct bpf_tramp_image *im;



	im = container_of(work, struct bpf_tramp_image, work);

	bpf_image_ksym_del(&im->ksym);

	bpf_jit_free_exec(im->image);

	bpf_jit_uncharge_modmem(PAGE_SIZE);
@@ -263,6 +260,14 @@ static void __bpf_tramp_image_put_deferred(struct work_struct *work) 
	kfree_rcu(im, rcu);

}



static void __bpf_tramp_image_put_deferred(struct work_struct *work)

{

	struct bpf_tramp_image *im;



	im = container_of(work, struct bpf_tramp_image, work);

	bpf_tramp_image_free(im);

}



/* callback, fexit step 3 or fentry step 2 */

static void __bpf_tramp_image_put_rcu(struct rcu_head *rcu)

{
@@ -437,7 +442,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut 
					  &tr->func.model, tr->flags, tlinks,

					  tr->func.addr);

	if (err < 0)

		goto out;

		goto out_free;



	set_memory_rox((long)im->image, 1);
@@ -466,7 +471,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut 
	}

#endif

	if (err)

		goto out;

		goto out_free;



	if (tr->cur_image)

		bpf_tramp_image_put(tr->cur_image);
@@ -477,6 +482,10 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut 
		tr->flags = orig_flags;

	kfree(tlinks);

	return err;



out_free:

	bpf_tramp_image_free(im);

	goto out;

}



static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)