[PATCH 6.4 127/800] bpf: Fix memleak due to fentry attach failure

Greg Kroah-Hartman
2023-07-16T19:58:44Z

From: Yafang Shao <laoar.shao@gmail.com>

[ Upstream commit 108598c39eefbedc9882273ac0df96127a629220 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/trampoline.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 84850e66ce3d6..78acf28d48732 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -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)
--
2.39.2