[PATCH bpf-next] bpf: test_run: Fix overflow in xdp frags bpf_test_finish

[Stanislav Fomichev <sdf@google.com>]

Syzkaller reports another issue:
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
check_copy_size include/linux/thread_info.h:230 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
copy_to_user include/linux/uaccess.h:199 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
bpf_test_finish.isra.0+0x4b2/0x680 net/bpf/test_run.c:171

This can happen when the userspace buffer is smaller than head+frags.
Return ENOSPC in this case.

Fixes: 7855e0db150a ("bpf: test_run: add xdp_shared_info pointer in bpf_test_finish signature")
Cc: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 net/bpf/test_run.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index f08034500813..eb129e48f90b 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -150,6 +150,11 @@ static int bpf_test_finish(const union bpf_attr *kattr,
 	if (data_out) {
 		int len = sinfo ? copy_size - sinfo->xdp_frags_size : copy_size;
 
+		if (len < 0) {
+			err = -ENOSPC;
+			goto out;
+		}
+
 		if (copy_to_user(data_out, data, len))
 			goto out;
 
-- 
2.35.1.574.g5d30c73bfb-goog