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Subject[PATCH 4.14 75/92] bpf: fix verifier NULL pointer dereference
Date
From: Craig Gallek <kraig@google.com>

commit 8c01c4f896aa3404af948880dcb29a2d51c833dc upstream.

do_check() can fail early without allocating env->cur_state under
memory pressure. Syzkaller found the stack below on the linux-next
tree because of this.

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 27062 Comm: syz-executor5 Not tainted 4.14.0-rc7+ #106
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801c2c74700 task.stack: ffff8801c3e28000
RIP: 0010:free_verifier_state kernel/bpf/verifier.c:347 [inline]
RIP: 0010:bpf_check+0xcf4/0x19c0 kernel/bpf/verifier.c:4533
RSP: 0018:ffff8801c3e2f5c8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 00000000fffffff4 RCX: 0000000000000000
RDX: 0000000000000070 RSI: ffffffff817d5aa9 RDI: 0000000000000380
RBP: ffff8801c3e2f668 R08: 0000000000000000 R09: 1ffff100387c5d9f
R10: 00000000218c4e80 R11: ffffffff85b34380 R12: ffff8801c4dc6a28
R13: 0000000000000000 R14: ffff8801c4dc6a00 R15: ffff8801c4dc6a20
FS: 00007f311079b700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004d4a24 CR3: 00000001cbcd0000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
bpf_prog_load+0xcbb/0x18e0 kernel/bpf/syscall.c:1166
SYSC_bpf kernel/bpf/syscall.c:1690 [inline]
SyS_bpf+0xae9/0x4620 kernel/bpf/syscall.c:1652
entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x452869
RSP: 002b:00007f311079abe8 EFLAGS: 00000212 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 0000000000758020 RCX: 0000000000452869
RDX: 0000000000000030 RSI: 0000000020168000 RDI: 0000000000000005
RBP: 00007f311079aa20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000004b7550
R13: 00007f311079ab58 R14: 00000000004b7560 R15: 0000000000000000
Code: df 48 c1 ea 03 80 3c 02 00 0f 85 e6 0b 00 00 4d 8b 6e 20 48 b8 00 00 00 00 00 fc ff df 49 8d bd 80 03 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 b6 0b 00 00 49 8b bd 80 03 00 00 e8 d6 0c 26
RIP: free_verifier_state kernel/bpf/verifier.c:347 [inline] RSP: ffff8801c3e2f5c8
RIP: bpf_check+0xcf4/0x19c0 kernel/bpf/verifier.c:4533 RSP: ffff8801c3e2f5c8
---[ end trace c8d37f339dc64004 ]---

Fixes: 638f5b90d460 ("bpf: reduce verifier memory consumption")
Fixes: 1969db47f8d0 ("bpf: fix verifier memory leaks")
Signed-off-by: Craig Gallek <kraig@google.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Balbir Singh <sblbir@amzn.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/bpf/verifier.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4777,8 +4777,10 @@ int bpf_check(struct bpf_prog **prog, un
env->allow_ptr_leaks = capable(CAP_SYS_ADMIN);

ret = do_check(env);
- free_verifier_state(env->cur_state, true);
- env->cur_state = NULL;
+ if (env->cur_state) {
+ free_verifier_state(env->cur_state, true);
+ env->cur_state = NULL;
+ }

skip_full_check:
while (!pop_stack(env, NULL, NULL));
@@ -4887,8 +4889,10 @@ int bpf_analyzer(struct bpf_prog *prog,
env->allow_ptr_leaks = capable(CAP_SYS_ADMIN);

ret = do_check(env);
- free_verifier_state(env->cur_state, true);
- env->cur_state = NULL;
+ if (env->cur_state) {
+ free_verifier_state(env->cur_state, true);
+ env->cur_state = NULL;
+ }

skip_full_check:
while (!pop_stack(env, NULL, NULL));

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