CVE-2024-42082: xdp: Remove WARN() from __xdp_reg_mem_model()

In the Linux kernel, the following vulnerability has been resolved:

xdp: Remove WARN() from xdpregmemmodel()

syzkaller reports a warning in xdpregmemmodel().

The warning occurs only if memidinithashtable() returns an error. It returns the error in two cases:

1. memory allocation fails; 2. rhashtableinit() fails when some fields of rhashtableparams struct are not initialized properly.

The second case cannot happen since there is a static const rhashtableparams struct with valid fields. So, warning is only triggered when there is a problem with memory allocation.

Thus, there is no sense in using WARN() to handle this error and it can be safely removed.

WARNING: CPU: 0 PID: 5065 at net/core/xdp.c:299 xdpregmemmodel+0x2d9/0x650 net/core/xdp.c:299

CPU: 0 PID: 5065 Comm: syz-executor883 Not tainted 6.8.0-syzkaller-05271-gf99c5f563c17 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024 RIP: 0010:xdpregmemmodel+0x2d9/0x650 net/core/xdp.c:299

Call Trace: xdpregmemmodel+0x22/0x40 net/core/xdp.c:344 xdptestrunsetup net/bpf/testrun.c:188 [inline] bpftestrunxdplive+0x365/0x1e90 net/bpf/testrun.c:377 bpfprogtestrunxdp+0x813/0x11b0 net/bpf/testrun.c:1267 bpfprogtestrun+0x33a/0x3b0 kernel/bpf/syscall.c:4240 sysbpf+0x48d/0x810 kernel/bpf/syscall.c:5649 dosysbpf kernel/bpf/syscall.c:5738 [inline] sesysbpf kernel/bpf/syscall.c:5736 [inline] x64sysbpf+0x7c/0x90 kernel/bpf/syscall.c:5736 dosyscall64+0xfb/0x240 entrySYSCALL64afterhwframe+0x6d/0x75

Found by Linux Verification Center (linuxtesting.org) with syzkaller.