linux-kernel - Re: CVE-2024-43910: bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds memory accesses

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Message-ID: <glynl6edraeb54cnasnykbnxrmkuujd6i6gfe76ps5voginajd@omnyfrjljyou>
Date: Wed, 28 Aug 2024 18:50:32 +0800
From: Shung-Hsi Yu <shung-hsi.yu@...e.com>
To: cve@...nel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, Eduard Zingerman <eddyz87@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>
Subject: Re: CVE-2024-43910: bpf: add missing check_func_arg_reg_off() to
 prevent out-of-bounds memory accesses

On Mon, Aug 26, 2024 at 12:17:18PM GMT, Greg Kroah-Hartman wrote:
> Description
> ===========
> 
> In the Linux kernel, the following vulnerability has been resolved:
> 
> bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds memory accesses
> 
> Currently, it's possible to pass in a modified CONST_PTR_TO_DYNPTR to
> a global function as an argument. The adverse effects of this is that
> BPF helpers can continue to make use of this modified
> CONST_PTR_TO_DYNPTR from within the context of the global function,
> which can unintentionally result in out-of-bounds memory accesses and
> therefore compromise overall system stability i.e.
> 
> [  244.157771] BUG: KASAN: slab-out-of-bounds in bpf_dynptr_data+0x137/0x140
> [  244.161345] Read of size 8 at addr ffff88810914be68 by task test_progs/302
> [  244.167151] CPU: 0 PID: 302 Comm: test_progs Tainted: G O E 6.10.0-rc3-00131-g66b586715063 #533
> [  244.174318] Call Trace:
> [  244.175787]  <TASK>
> [  244.177356]  dump_stack_lvl+0x66/0xa0
> [  244.179531]  print_report+0xce/0x670
> [  244.182314]  ? __virt_addr_valid+0x200/0x3e0
> [  244.184908]  kasan_report+0xd7/0x110
> [  244.187408]  ? bpf_dynptr_data+0x137/0x140
> [  244.189714]  ? bpf_dynptr_data+0x137/0x140
> [  244.192020]  bpf_dynptr_data+0x137/0x140
> [  244.194264]  bpf_prog_b02a02fdd2bdc5fa_global_call_bpf_dynptr_data+0x22/0x26
> [  244.198044]  bpf_prog_b0fe7b9d7dc3abde_callback_adjust_bpf_dynptr_reg_off+0x1f/0x23
> [  244.202136]  bpf_user_ringbuf_drain+0x2c7/0x570
> [  244.204744]  ? 0xffffffffc0009e58
> [  244.206593]  ? __pfx_bpf_user_ringbuf_drain+0x10/0x10
> [  244.209795]  bpf_prog_33ab33f6a804ba2d_user_ringbuf_callback_const_ptr_to_dynptr_reg_off+0x47/0x4b
> [  244.215922]  bpf_trampoline_6442502480+0x43/0xe3
> [  244.218691]  __x64_sys_prlimit64+0x9/0xf0
> [  244.220912]  do_syscall_64+0xc1/0x1d0
> [  244.223043]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> [  244.226458] RIP: 0033:0x7ffa3eb8f059
> [  244.228582] Code: 08 89 e8 5b 5d c3 66 2e 0f 1f 84 00 00 00 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 8b 0d 8f 1d 0d 00 f7 d8 64 89 01 48
> [  244.241307] RSP: 002b:00007ffa3e9c6eb8 EFLAGS: 00000206 ORIG_RAX: 000000000000012e
> [  244.246474] RAX: ffffffffffffffda RBX: 00007ffa3e9c7cdc RCX: 00007ffa3eb8f059
> [  244.250478] RDX: 00007ffa3eb162b4 RSI: 0000000000000000 RDI: 00007ffa3e9c7fb0
> [  244.255396] RBP: 00007ffa3e9c6ed0 R08: 00007ffa3e9c76c0 R09: 0000000000000000
> [  244.260195] R10: 0000000000000000 R11: 0000000000000206 R12: ffffffffffffff80
> [  244.264201] R13: 000000000000001c R14: 00007ffc5d6b4260 R15: 00007ffa3e1c7000
> [  244.268303]  </TASK>
> 
> Add a check_func_arg_reg_off() to the path in which the BPF verifier
> verifies the arguments of global function arguments, specifically
> those which take an argument of type ARG_PTR_TO_DYNPTR |
> MEM_RDONLY. Also, process_dynptr_func() doesn't appear to perform any
> explicit and strict type matching on the supplied register type, so
> let's also enforce that a register either type PTR_TO_STACK or
> CONST_PTR_TO_DYNPTR is by the caller.
> 
> The Linux kernel CVE team has assigned CVE-2024-43910 to this issue.
> 
> 
> Affected and fixed versions
> ===========================
> 
> 	Fixed in 6.10.5 with commit 13663a7c644b
> 	Fixed in 6.11-rc1 with commit ec2b9a5e11e5

I believe the issue of being able to pass modified (i.e. non-zero
offset) dynptr to global function was introduced with commit
a64bfe618665 ("bpf: add support for passing dynptr pointer to global
subprog") in 6.8.

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