CVE-2024-56658: net: defer final 'struct net' free in netns dismantle

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

net: defer final 'struct net' free in netns dismantle

Ilya reported a slab-use-after-free in dstdestroy [1]

Issue is in xfrm6netinit() and xfrm4netinit() :

They copy xfrm[46]dstopstemplate into net->xfrm.xfrm[46]dstops.

But net structure might be freed before all the dst callbacks are called. So when dstdestroy() calls later :

if (dst->ops->destroy) dst->ops->destroy(dst);

dst->ops points to the old net->xfrm.xfrm[46]dstops, which has been freed.

See a relevant issue fixed in :

ac888d58869b ("net: do not delay dstentriesadd() in dstrelease()")

A fix is to queue the 'struct net' to be freed after one another cleanupnet() round (and existing rcubarrier())

[1]

BUG: KASAN: slab-use-after-free in dstdestroy (net/core/dst.c:112) Read of size 8 at addr ffff8882137ccab0 by task swapper/37/0 Dec 03 05:46:18 kernel: CPU: 37 UID: 0 PID: 0 Comm: swapper/37 Kdump: loaded Not tainted 6.12.0 #67 Hardware name: Red Hat KVM/RHEL, BIOS 1.16.1-1.el9 04/01/2014 Call Trace: <IRQ> dumpstacklvl (lib/dumpstack.c:124) printaddressdescription.constprop.0 (mm/kasan/report.c:378) ? dstdestroy (net/core/dst.c:112) printreport (mm/kasan/report.c:489) ? dstdestroy (net/core/dst.c:112) ? kasanaddrtoslab (mm/kasan/common.c:37) kasanreport (mm/kasan/report.c:603) ? dstdestroy (net/core/dst.c:112) ? rcudobatch (kernel/rcu/tree.c:2567) dstdestroy (net/core/dst.c:112) rcudobatch (kernel/rcu/tree.c:2567) ? pfxrcudobatch (kernel/rcu/tree.c:2491) ? lockdephardirqsonprepare (kernel/locking/lockdep.c:4339 kernel/locking/lockdep.c:4406) rcucore (kernel/rcu/tree.c:2825) handlesoftirqs (kernel/softirq.c:554) irqexitrcu (kernel/softirq.c:589 kernel/softirq.c:428 kernel/softirq.c:637) irqexitrcu (kernel/softirq.c:651) sysvecapictimerinterrupt (arch/x86/kernel/apic/apic.c:1049 arch/x86/kernel/apic/apic.c:1049) </IRQ> <TASK> asmsysvecapictimerinterrupt (./arch/x86/include/asm/idtentry.h:702) RIP: 0010:defaultidle (./arch/x86/include/asm/irqflags.h:37 ./arch/x86/include/asm/irqflags.h:92 arch/x86/kernel/process.c:743) Code: 00 4d 29 c8 4c 01 c7 4c 29 c2 e9 6e ff ff ff 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 90 0f 00 2d c7 c9 27 00 fb f4 <fa> c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 90 RSP: 0018:ffff888100d2fe00 EFLAGS: 00000246 RAX: 00000000001870ed RBX: 1ffff110201a5fc2 RCX: ffffffffb61a3e46 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffb3d4d123 RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed11c7e1835d R10: ffff888e3f0c1aeb R11: 0000000000000000 R12: 0000000000000000 R13: ffff888100d20000 R14: dffffc0000000000 R15: 0000000000000000 ? ctkernelexit.constprop.0 (kernel/contexttracking.c:148) ? cpuidleidlecall (kernel/sched/idle.c:186) defaultidlecall (./include/linux/cpuidle.h:143 kernel/sched/idle.c:118) cpuidleidlecall (kernel/sched/idle.c:186) ? pfxcpuidleidlecall (kernel/sched/idle.c:168) ? lockrelease (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5848) ? lockdephardirqsonprepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406) ? tscverifytscadjust (arch/x86/kernel/tscsync.c:59) doidle (kernel/sched/idle.c:326) cpustartupentry (kernel/sched/idle.c:423 (discriminator 1)) startsecondary (arch/x86/kernel/smpboot.c:202 arch/x86/kernel/smpboot.c:282) ? pfxstartsecondary (arch/x86/kernel/smpboot.c:232) ? softrestartcpu (arch/x86/kernel/head64.S:452) commonstartup64 (arch/x86/kernel/head64.S:414) </TASK> Dec 03 05:46:18 kernel: Allocated by task 12184: kasansavestack (mm/kasan/common.c:48) kasansavetrack (./arch/x86/include/asm/current.h:49 mm/kasan/common.c:60 mm/kasan/common.c:69) kasanslaballoc (mm/kasan/common.c:319 mm/kasan/common.c:345) kmemcacheallocnoprof (mm/slub.c:4085 mm/slub.c:4134 mm/slub.c:4141) copynetns (net/core/netnamespace.c:421 net/core/netnamespace.c:480) createnewnamespaces ---truncated---