bpf: test_run: Fix overflow in xdp frags parsing

bpf: test_run: Fix overflow in xdp frags parsing

When kattr->test.data_size_in > INT_MAX, signed min_t will assign
negative value to data_len. This negative value then gets passed
over to copy_from_user where it is converted to (big) unsigned.

Use unsigned min_t to avoid this overflow.

usercopy: Kernel memory overwrite attempt detected to wrapped address
(offset 0, size 18446612140539162846)!
------------[ cut here ]------------
kernel BUG at mm/usercopy.c:102!
invalid opcode: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 0 PID: 3781 Comm: syz-executor226 Not tainted 4.15.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:usercopy_abort+0xbd/0xbf mm/usercopy.c:102
RSP: 0018:ffff8801e9703a38 EFLAGS: 00010286
RAX: 000000000000006c RBX: ffffffff84fc7040 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff816560a2 RDI: ffffed003d2e0739
RBP: ffff8801e9703a90 R08: 000000000000006c R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff84fc73a0
R13: ffffffff84fc7180 R14: ffffffff84fc7040 R15: ffffffff84fc7040
FS:  00007f54e0bec300(0000) GS:ffff8801f6600000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000280 CR3: 00000001e90ea000 CR4: 00000000003426f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 check_bogus_address mm/usercopy.c:155 [inline]
 __check_object_size mm/usercopy.c:263 [inline]
 __check_object_size.cold+0x8c/0xad mm/usercopy.c:253
 check_object_size include/linux/thread_info.h:112 [inline]
 check_copy_size include/linux/thread_info.h:143 [inline]
 copy_from_user include/linux/uaccess.h:142 [inline]
 bpf_prog_test_run_xdp+0xe57/0x1240 net/bpf/test_run.c:989
 bpf_prog_test_run kernel/bpf/syscall.c:3377 [inline]
 __sys_bpf+0xdf2/0x4a50 kernel/bpf/syscall.c:4679
 SYSC_bpf kernel/bpf/syscall.c:4765 [inline]
 SyS_bpf+0x26/0x50 kernel/bpf/syscall.c:4763
 do_syscall_64+0x21a/0x3e0 arch/x86/entry/common.c:305
 entry_SYSCALL_64_after_hwframe+0x46/0xbb

Fixes: 1c1949982524 ("bpf: introduce frags support to bpf_prog_test_run_xdp()")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220204235849.14658-1-sdf@google.com