[PATCH bpf v3] bpf: Fix memory leaks in __check_func_call

[Wang Yufen <wangyufen@xxxxxxxxxx>]

kmemleak reports this issue:

unreferenced object 0xffff88817139d000 (size 2048):
  comm "test_progs", pid 33246, jiffies 4307381979 (age 45851.820s)
  hex dump (first 32 bytes):
    01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<0000000045f075f0>] kmalloc_trace+0x27/0xa0
    [<0000000098b7c90a>] __check_func_call+0x316/0x1230
    [<00000000b4c3c403>] check_helper_call+0x172e/0x4700
    [<00000000aa3875b7>] do_check+0x21d8/0x45e0
    [<000000001147357b>] do_check_common+0x767/0xaf0
    [<00000000b5a595b4>] bpf_check+0x43e3/0x5bc0
    [<0000000011e391b1>] bpf_prog_load+0xf26/0x1940
    [<0000000007f765c0>] __sys_bpf+0xd2c/0x3650
    [<00000000839815d6>] __x64_sys_bpf+0x75/0xc0
    [<00000000946ee250>] do_syscall_64+0x3b/0x90
    [<0000000000506b7f>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

The root case here is: In function prepare_func_exit(), the callee is
not released in the abnormal scenario after "state->curframe--;". To
fix, move "state->curframe--;" to the very bottom of the function,
right when we free callee and reset frame[] pointer to NULL, as Andrii
suggested.

In addition, function __check_func_call() has a similar problem. In
the abnormal scenario before "state->curframe++;", the callee is alse
not released.

Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
Fixes: fd978bf7fd31 ("bpf: Add reference tracking to verifier")
Signed-off-by: Wang Yufen <wangyufen@xxxxxxxxxx>
---
 kernel/bpf/verifier.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7f0a9f6..eff7a5a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6736,11 +6736,11 @@ static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 	/* Transfer references to the callee */
 	err = copy_reference_state(callee, caller);
 	if (err)
-		return err;
+		goto err_out;
 
 	err = set_callee_state_cb(env, caller, callee, *insn_idx);
 	if (err)
-		return err;
+		goto err_out;
 
 	clear_caller_saved_regs(env, caller->regs);
 
@@ -6757,6 +6757,11 @@ static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 		print_verifier_state(env, callee, true);
 	}
 	return 0;
+
+err_out:
+	kfree(callee);
+	state->frame[state->curframe + 1] = NULL;
+	return err;
 }
 
 int map_set_for_each_callback_args(struct bpf_verifier_env *env,
@@ -6970,8 +6975,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 		return -EINVAL;
 	}
 
-	state->curframe--;
-	caller = state->frame[state->curframe];
+	caller = state->frame[state->curframe - 1];
 	if (callee->in_callback_fn) {
 		/* enforce R0 return value range [0, 1]. */
 		struct tnum range = callee->callback_ret_range;
@@ -7001,6 +7005,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 			return err;
 	}
 
+	state->curframe--;
 	*insn_idx = callee->callsite + 1;
 	if (env->log.level & BPF_LOG_LEVEL) {
 		verbose(env, "returning from callee:\n");
-- 
1.8.3.1