On Wed, 19 Jun 2024 at 10:29, Matt Bobrowski <mattbobrowski@xxxxxxxxxx> wrote: > > 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. Lastly, we also add a new > negative test which catches this regression. > > Reported-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> > Signed-off-by: Matt Bobrowski <mattbobrowski@xxxxxxxxxx> > --- Acked-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> As we discussed offline, once you respin, it'd be best to split selftests and the fix into two, and probably add one more for the lack of reg->type check (if it's possible to trigger without this fix), and extend the commit log accordingly. Apart from that, fix & test lgtm!
