CVE-2025-21653: net_sched: cls_flow: validate TCA_FLOW_RSHIFT attribute

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

netsched: clsflow: validate TCAFLOWRSHIFT attribute

syzbot found that TCAFLOWRSHIFT attribute was not validated. Right shitfing a 32bit integer is undefined for large shift values.

UBSAN: shift-out-of-bounds in net/sched/clsflow.c:329:23 shift exponent 9445 is too large for 32-bit type 'u32' (aka 'unsigned int') CPU: 1 UID: 0 PID: 54 Comm: kworker/u8:3 Not tainted 6.13.0-rc3-syzkaller-00180-g4f619d518db9 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 Workqueue: ipv6addrconf addrconfdadwork Call Trace: <TASK> dumpstack lib/dumpstack.c:94 [inline] dumpstacklvl+0x241/0x360 lib/dumpstack.c:120 ubsanepilogue lib/ubsan.c:231 [inline] ubsanhandleshiftoutofbounds+0x3c8/0x420 lib/ubsan.c:468 flowclassify+0x24d5/0x25b0 net/sched/clsflow.c:329 tcclassify include/net/tcwrapper.h:197 [inline] tcfclassify net/sched/clsapi.c:1771 [inline] tcfclassify+0x420/0x1160 net/sched/clsapi.c:1867 sfbclassify net/sched/schsfb.c:260 [inline] sfbenqueue+0x3ad/0x18b0 net/sched/schsfb.c:318 devqdiscenqueue+0x4b/0x290 net/core/dev.c:3793 devxmitskb net/core/dev.c:3889 [inline] devqueuexmit+0xf0e/0x3f50 net/core/dev.c:4400 devqueuexmit include/linux/netdevice.h:3168 [inline] neighhhoutput include/net/neighbour.h:523 [inline] neighoutput include/net/neighbour.h:537 [inline] ipfinishoutput2+0xd41/0x1390 net/ipv4/ipoutput.c:236 iptunnelxmit+0x55d/0x9b0 net/ipv4/iptunnelcore.c:82 udptunnelxmitskb+0x262/0x3b0 net/ipv4/udptunnelcore.c:173 genevexmitskb drivers/net/geneve.c:916 [inline] genevexmit+0x21dc/0x2d00 drivers/net/geneve.c:1039 netdevstartxmit include/linux/netdevice.h:5002 [inline] netdevstartxmit include/linux/netdevice.h:5011 [inline] xmitone net/core/dev.c:3590 [inline] devhardstartxmit+0x27a/0x7d0 net/core/dev.c:3606 devqueuexmit+0x1b73/0x3f50 net/core/dev.c:4434