Message-ID: <c11f1caa46535ebb102d1ed2bba83bf257ef6939.camel@gmail.com>
Date: Fri, 14 Mar 2025 14:08:29 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Kohei Enju <enjuk@...zon.com>, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
 <daniel@...earbox.net>,  John Fastabend <john.fastabend@...il.com>, Andrii
 Nakryiko <andrii@...nel.org>, Martin KaFai Lau	 <martin.lau@...ux.dev>,
 Song Liu <song@...nel.org>, Yonghong Song	 <yonghong.song@...ux.dev>, KP
 Singh <kpsingh@...nel.org>, Stanislav Fomichev	 <sdf@...ichev.me>, Hao Luo
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,  Peilin Ye
 <yepeilin@...gle.com>, Ilya Leoshkevich <iii@...ux.ibm.com>, Kuniyuki
 Iwashima	 <kuniyu@...zon.com>, kohei.enju@...il.com, 
	syzbot+a5964227adc0f904549c@...kaller.appspotmail.com
Subject: Re: [PATCH bpf-next v1] bpf: Fix out-of-bounds read in
 check_atomic_load/store()

On Sat, 2025-03-15 at 04:54 +0900, Kohei Enju wrote:
> syzbot reported the following splat [0].
> 
> In check_atomic_load/store(), register validity is not checked before
> atomic_ptr_type_ok(). This causes the out-of-bounds read in is_ctx_reg()
> called from atomic_ptr_type_ok() when the register number is MAX_BPF_REG
> or greater.
> 
> Add check_reg_arg() before atomic_ptr_type_ok(), and return early when
> the register is invalid.
> 
> [0]
>  BUG: KASAN: slab-out-of-bounds in is_ctx_reg kernel/bpf/verifier.c:6185 [inline]
>  BUG: KASAN: slab-out-of-bounds in atomic_ptr_type_ok+0x3d7/0x550 kernel/bpf/verifier.c:6223
>  Read of size 4 at addr ffff888141b0d690 by task syz-executor143/5842
> 
>  CPU: 1 UID: 0 PID: 5842 Comm: syz-executor143 Not tainted 6.14.0-rc3-syzkaller-gf28214603dc6 #0
>  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
>  Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:94 [inline]
>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>   print_address_description mm/kasan/report.c:408 [inline]
>   print_report+0x16e/0x5b0 mm/kasan/report.c:521
>   kasan_report+0x143/0x180 mm/kasan/report.c:634
>   is_ctx_reg kernel/bpf/verifier.c:6185 [inline]
>   atomic_ptr_type_ok+0x3d7/0x550 kernel/bpf/verifier.c:6223
>   check_atomic_store kernel/bpf/verifier.c:7804 [inline]
>   check_atomic kernel/bpf/verifier.c:7841 [inline]
>   do_check+0x89dd/0xedd0 kernel/bpf/verifier.c:19334
>   do_check_common+0x1678/0x2080 kernel/bpf/verifier.c:22600
>   do_check_main kernel/bpf/verifier.c:22691 [inline]
>   bpf_check+0x165c8/0x1cca0 kernel/bpf/verifier.c:23821
>   bpf_prog_load+0x1664/0x20e0 kernel/bpf/syscall.c:2967
>   __sys_bpf+0x4ea/0x820 kernel/bpf/syscall.c:5811
>   __do_sys_bpf kernel/bpf/syscall.c:5918 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:5916 [inline]
>   __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5916
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
>  RIP: 0033:0x7fa3ac86bab9
>  Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
>  RSP: 002b:00007ffe50fff5f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
>  RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fa3ac86bab9
>  RDX: 0000000000000094 RSI: 00004000000009c0 RDI: 0000000000000005
>  RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000006
>  R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
>  R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001
>   </TASK>
> 
>  Allocated by task 5842:
>   kasan_save_stack mm/kasan/common.c:47 [inline]
>   kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
>   poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
>   __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:394
>   kasan_kmalloc include/linux/kasan.h:260 [inline]
>   __kmalloc_cache_noprof+0x243/0x390 mm/slub.c:4325
>   kmalloc_noprof include/linux/slab.h:901 [inline]
>   kzalloc_noprof include/linux/slab.h:1037 [inline]
>   do_check_common+0x1ec/0x2080 kernel/bpf/verifier.c:22499
>   do_check_main kernel/bpf/verifier.c:22691 [inline]
>   bpf_check+0x165c8/0x1cca0 kernel/bpf/verifier.c:23821
>   bpf_prog_load+0x1664/0x20e0 kernel/bpf/syscall.c:2967
>   __sys_bpf+0x4ea/0x820 kernel/bpf/syscall.c:5811
>   __do_sys_bpf kernel/bpf/syscall.c:5918 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:5916 [inline]
>   __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5916
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
>  The buggy address belongs to the object at ffff888141b0d000
>   which belongs to the cache kmalloc-2k of size 2048
>  The buggy address is located 312 bytes to the right of
>   allocated 1368-byte region [ffff888141b0d000, ffff888141b0d558)
> 
>  The buggy address belongs to the physical page:
>  page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x141b08
>  head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
>  flags: 0x57ff00000000040(head|node=1|zone=2|lastcpupid=0x7ff)
>  page_type: f5(slab)
>  raw: 057ff00000000040 ffff88801b042000 dead000000000100 dead000000000122
>  raw: 0000000000000000 0000000080080008 00000000f5000000 0000000000000000
>  head: 057ff00000000040 ffff88801b042000 dead000000000100 dead000000000122
>  head: 0000000000000000 0000000080080008 00000000f5000000 0000000000000000
>  head: 057ff00000000003 ffffea000506c201 ffffffffffffffff 0000000000000000
>  head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
>  page dumped because: kasan: bad access detected
>  page_owner tracks the page as allocated
>  page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 8909973200, free_ts 0
>   set_page_owner include/linux/page_owner.h:32 [inline]
>   post_alloc_hook+0x1f4/0x240 mm/page_alloc.c:1585
>   prep_new_page mm/page_alloc.c:1593 [inline]
>   get_page_from_freelist+0x3a8c/0x3c20 mm/page_alloc.c:3538
>   __alloc_frozen_pages_noprof+0x264/0x580 mm/page_alloc.c:4805
>   alloc_pages_mpol+0x311/0x660 mm/mempolicy.c:2270
>   alloc_slab_page mm/slub.c:2423 [inline]
>   allocate_slab+0x8f/0x3a0 mm/slub.c:2587
>   new_slab mm/slub.c:2640 [inline]
>   ___slab_alloc+0xc27/0x14a0 mm/slub.c:3826
>   __slab_alloc+0x58/0xa0 mm/slub.c:3916
>   __slab_alloc_node mm/slub.c:3991 [inline]
>   slab_alloc_node mm/slub.c:4152 [inline]
>   __kmalloc_cache_noprof+0x27b/0x390 mm/slub.c:4320
>   kmalloc_noprof include/linux/slab.h:901 [inline]
>   kzalloc_noprof include/linux/slab.h:1037 [inline]
>   virtio_pci_probe+0x54/0x340 drivers/virtio/virtio_pci_common.c:689
>   local_pci_probe drivers/pci/pci-driver.c:324 [inline]
>   pci_call_probe drivers/pci/pci-driver.c:392 [inline]
>   __pci_device_probe drivers/pci/pci-driver.c:417 [inline]
>   pci_device_probe+0x6c5/0xa10 drivers/pci/pci-driver.c:451
>   really_probe+0x2b9/0xad0 drivers/base/dd.c:658
>   __driver_probe_device+0x1a2/0x390 drivers/base/dd.c:800
>   driver_probe_device+0x50/0x430 drivers/base/dd.c:830
>   __driver_attach+0x45f/0x710 drivers/base/dd.c:1216
>   bus_for_each_dev+0x239/0x2b0 drivers/base/bus.c:370
>   bus_add_driver+0x346/0x670 drivers/base/bus.c:678
>  page_owner free stack trace missing
> 
>  Memory state around the buggy address:
>   ffff888141b0d580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>   ffff888141b0d600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  >ffff888141b0d680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>                           ^
>   ffff888141b0d700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>   ffff888141b0d780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> 
> Reported-by: syzbot+a5964227adc0f904549c@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=a5964227adc0f904549c
> Tested-by: syzbot+a5964227adc0f904549c@...kaller.appspotmail.com
> Fixes: e24bbad29a8d ("bpf: Introduce load-acquire and store-release instructions")
> Signed-off-by: Kohei Enju <enjuk@...zon.com>
> ---

I wonder if we have test cases for malformed instructions.
Maybe add one since this issue was hit?

>  kernel/bpf/verifier.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 3303a3605ee8..6481604ab612 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -7788,6 +7788,12 @@ static int check_atomic_rmw(struct bpf_verifier_env *env,
>  static int check_atomic_load(struct bpf_verifier_env *env,
>  			     struct bpf_insn *insn)
>  {
> +	int err;
> +
> +	err = check_reg_arg(env, insn->src_reg, SRC_OP);
> +	if (err)
> +		return err;
> +

I agree with these changes, however, both check_load_mem() and
check_store_reg() already do check_reg_arg() first thing.
Maybe just swap the atomic_ptr_type_ok() and check_load_mem()?

>  	if (!atomic_ptr_type_ok(env, insn->src_reg, insn)) {
>  		verbose(env, "BPF_ATOMIC loads from R%d %s is not allowed\n",
>  			insn->src_reg,
> @@ -7801,6 +7807,12 @@ static int check_atomic_load(struct bpf_verifier_env *env,
>  static int check_atomic_store(struct bpf_verifier_env *env,
>  			      struct bpf_insn *insn)
>  {
> +	int err;
> +
> +	err = check_reg_arg(env, insn->dst_reg, SRC_OP);
> +	if (err)
> +		return err;
> +
>  	if (!atomic_ptr_type_ok(env, insn->dst_reg, insn)) {
>  		verbose(env, "BPF_ATOMIC stores into R%d %s is not allowed\n",
>  			insn->dst_reg,

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