CVE-2025-38666: net: appletalk: Fix use-after-free in AARP proxy probe

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

net: appletalk: Fix use-after-free in AARP proxy probe

The AARP proxy‐probe routine (aarpproxyprobenetwork) sends a probe, releases the aarplock, sleeps, then re-acquires the lock. During that window an expire timer thread (aarpexpiretimer) can remove and kfree() the same entry, leading to a use-after-free.

race condition:

cpu 0 | cpu 1 atalksendmsg() | atifproxyprobedevice() aarpsendddp() | aarpproxyprobenetwork() modtimer() | lock(aarplock) // LOCK!! timeout around 200ms | alloc(aarpentry) and then call | proxies[hash] = aarpentry aarpexpiretimeout() | aarpsendprobe() | unlock(aarplock) // UNLOCK!! lock(aarplock) // LOCK!! | msleep(100); aarpexpiretimer(&proxies[ct]) | free(aarpentry) | unlock(aarplock) // UNLOCK!! | | lock(aarplock) // LOCK!! | UAF aarpentry !!

================================================================== BUG: KASAN: slab-use-after-free in aarpproxyprobenetwork+0x560/0x630 net/appletalk/aarp.c:493 Read of size 4 at addr ffff8880123aa360 by task repro/13278

CPU: 3 UID: 0 PID: 13278 Comm: repro Not tainted 6.15.2 #3 PREEMPT(full) Call Trace: <TASK> dumpstack lib/dumpstack.c:94 [inline] dumpstacklvl+0x116/0x1b0 lib/dumpstack.c:120 printaddressdescription mm/kasan/report.c:408 [inline] printreport+0xc1/0x630 mm/kasan/report.c:521 kasanreport+0xca/0x100 mm/kasan/report.c:634 aarpproxyprobenetwork+0x560/0x630 net/appletalk/aarp.c:493 atifproxyprobedevice net/appletalk/ddp.c:332 [inline] atifioctl+0xb58/0x16c0 net/appletalk/ddp.c:857 atalkioctl+0x198/0x2f0 net/appletalk/ddp.c:1818 sockdoioctl+0xdc/0x260 net/socket.c:1190 sockioctl+0x239/0x6a0 net/socket.c:1311 vfsioctl fs/ioctl.c:51 [inline] dosysioctl fs/ioctl.c:906 [inline] sesysioctl fs/ioctl.c:892 [inline] x64sysioctl+0x194/0x200 fs/ioctl.c:892 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xcb/0x250 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f </TASK>

Allocated: aarpalloc net/appletalk/aarp.c:382 [inline] aarpproxyprobenetwork+0xd8/0x630 net/appletalk/aarp.c:468 atifproxyprobedevice net/appletalk/ddp.c:332 [inline] atifioctl+0xb58/0x16c0 net/appletalk/ddp.c:857 atalkioctl+0x198/0x2f0 net/appletalk/ddp.c:1818

Freed: kfree+0x148/0x4d0 mm/slub.c:4841 aarpexpire net/appletalk/aarp.c:90 [inline] aarpexpiretimer net/appletalk/aarp.c:261 [inline] aarpexpiretimeout+0x480/0x6e0 net/appletalk/aarp.c:317

The buggy address belongs to the object at ffff8880123aa300 which belongs to the cache kmalloc-192 of size 192 The buggy address is located 96 bytes inside of freed 192-byte region [ffff8880123aa300, ffff8880123aa3c0)

Memory state around the buggy address: ffff8880123aa200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff8880123aa280: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc ffff8880123aa300: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8880123aa380: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff8880123aa400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ==================================================================