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bpf: Fix memleak due to fentry attach failure

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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: e21aa341785c ("bpf: Fix fexit trampoline.")
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <song@kernel.org>
Cc: Jiri Olsa <olsajiri@gmail.com>
Link: https://lore.kernel.org/bpf/20230515130849.57502-2-laoar.shao@gmail.com
This commit is contained in:
Yafang Shao 2023-05-15 13:08:47 +00:00 committed by Daniel Borkmann
parent 47e79cbeea
commit 108598c39e
1 changed files with 15 additions and 6 deletions
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21
kernel/bpf/trampoline.c
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@ -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 @@ again:
&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 @@ again:
}
#endif
if (err)
goto out;
goto out_free;
if (tr->cur_image)
bpf_tramp_image_put(tr->cur_image);
@ -477,6 +482,10 @@ out:
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)