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 91d8de938a3dd..30af8f66e17b4 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -279,11 +279,8 @@ 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); @@ -291,6 +288,14 @@ 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) { @@ -465,7 +470,7 @@ 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_ro((long)im->image, 1); set_memory_x((long)im->image, 1); @@ -495,7 +500,7 @@ 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); @@ -506,6 +511,10 @@ 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)