CVE: CVE-2024-43910
Published: 2024-08-26
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_[PII_REDACTED]+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:[PII_REDACTED]00012e
[  244.246474] RAX: ffffffffffffffda RBX: 00007ffa3e9c7cdc RCX: 00007ffa3eb8f059
[  244.250478] RDX: 00007ffa3eb162b4 RSI: [PII_REDACTED] RDI: 00007ffa3e9c7fb0
[  244.255396] RBP: 00007ffa3e9c6ed0 R08: 00007ffa3e9c76c0 R09: [PII_REDACTED]
[  244.260195] R10: [PII_REDACTED] R11: [PII_REDACTED] R12: ffffffffffffff80
[  244.264201] R13:[PII_REDACTED]00001c 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.
CVSS Score: 5.5 (MEDIUM)
CWE: CWE-787
References: https://git.kernel.org/stable/c/13663a7c644bf1dedaf461d07252db5d76c8759a; https://git.kernel.org/stable/c/ec2b9a5e11e51fea1bb04c1e7e471952e887e874