On Thu, Feb 03, 2022 at 11:17:27AM -0800, Yonghong Song wrote: > syzbot reported a btf decl_tag bug with stack trace below: > > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] > CPU: 0 PID: 3592 Comm: syz-executor914 Not tainted 5.16.0-syzkaller-11424-gb7892f7d5cb2 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:btf_type_vlen include/linux/btf.h:231 [inline] > RIP: 0010:btf_decl_tag_resolve+0x83e/0xaa0 kernel/bpf/btf.c:3910 > ... > Call Trace: > <TASK> > btf_resolve+0x251/0x1020 kernel/bpf/btf.c:4198 > btf_check_all_types kernel/bpf/btf.c:4239 [inline] > btf_parse_type_sec kernel/bpf/btf.c:4280 [inline] > btf_parse kernel/bpf/btf.c:4513 [inline] > btf_new_fd+0x19fe/0x2370 kernel/bpf/btf.c:6047 > bpf_btf_load kernel/bpf/syscall.c:4039 [inline] > __sys_bpf+0x1cbb/0x5970 kernel/bpf/syscall.c:4679 > __do_sys_bpf kernel/bpf/syscall.c:4738 [inline] > __se_sys_bpf kernel/bpf/syscall.c:4736 [inline] > __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:4736 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > The kasan error is triggered with an illegal BTF like below: > type 0: void > type 1: int > type 2: decl_tag to func type 3 > type 3: func to func_proto type 8 > The total number of types is 4 and the type 3 is illegal > since its func_proto type is out of range. > > Currently, the target type of decl_tag can be struct/union, var or func. > Both struct/union and var implemented their own 'resolve' callback functions > and hence handled properly in kernel. > But func type doesn't have 'resolve' callback function. When > btf_decl_tag_resolve() tries to check func type, it tries to get > vlen of its func_proto type, which triggered the above kasan error. > > To fix the issue, btf_decl_tag_resolve() needs to do btf_func_check() > before trying to accessing func_proto type. > In the current implementation, func type is checked with > btf_func_check() in the main checking function btf_check_all_types(). > To fix the above kasan issue, let us implement 'resolve' callback > func type properly. The 'resolve' callback will be also called > in btf_check_all_types() for func types. Acked-by: Martin KaFai Lau <kafai@xxxxxx>
