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From: Alexei Starovoitov <>
To: "David S . Miller" <>
Cc: Daniel Borkmann <>, <>
Subject: [PATCH bpf-next] bpf: fix verifier GPF in kmalloc failure path
Date: Fri, 5 Jan 2018 12:57:11 -0800	[thread overview]
Message-ID: <> (raw)

syzbot reported the following panic in the verifier triggered
by kmalloc error injection:

kasan: GPF could be caused by NULL-ptr deref or user memory access
RIP: 0010:copy_func_state kernel/bpf/verifier.c:403 [inline]
RIP: 0010:copy_verifier_state+0x364/0x590 kernel/bpf/verifier.c:431
Call Trace:
 pop_stack+0x8c/0x270 kernel/bpf/verifier.c:449
 push_stack kernel/bpf/verifier.c:491 [inline]
 check_cond_jmp_op kernel/bpf/verifier.c:3598 [inline]
 do_check+0x4b60/0xa050 kernel/bpf/verifier.c:4731
 bpf_check+0x3296/0x58c0 kernel/bpf/verifier.c:5489
 bpf_prog_load+0xa2a/0x1b00 kernel/bpf/syscall.c:1198
 SYSC_bpf kernel/bpf/syscall.c:1807 [inline]
 SyS_bpf+0x1044/0x4420 kernel/bpf/syscall.c:1769

when copy_verifier_state() aborts in the middle due to kmalloc failure
some of the frames could have been partially copied while
current free_verifier_state() loop
for (i = 0; i <= state->curframe; i++)
assumed that all frames are non-null.
Simply fix it by adding 'if (!state)' to free_func_state().
Also avoid stressing copy frame logic more if kzalloc fails
in push_stack() free env->cur_state right away.

Signed-off-by: Alexei Starovoitov <>
 kernel/bpf/verifier.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a2b211262c25..d921ab387b0b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -375,6 +375,8 @@ static int realloc_func_state(struct bpf_func_state *state, int size,
 static void free_func_state(struct bpf_func_state *state)
+	if (!state)
+		return;
@@ -487,6 +489,8 @@ static struct bpf_verifier_state *push_stack(struct bpf_verifier_env *env,
 	return &elem->st;
+	free_verifier_state(env->cur_state, true);
+	env->cur_state = NULL;
 	/* pop all elements and return */
 	while (!pop_stack(env, NULL, NULL));
 	return NULL;

             reply	other threads:[~2018-01-05 20:57 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-05 20:57 Alexei Starovoitov [this message]
2018-01-08 15:51 [PATCH bpf-next] bpf: fix verifier GPF in kmalloc failure path Alexei Starovoitov
2018-01-08 17:33 ` Daniel Borkmann

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