CVE-2025-38323: net: atm: add lec_mutex

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

net: atm: add lecmutex

syzbot found its way in net/atm/lec.c, and found an error path in lecdattach() could leave a dangling pointer in devlec[].

Add a mutex to protect devlecp[] uses from lecdattach(), lecvccattach() and lecmcastattach().

Following patch will use this mutex for /proc/net/atm/lec.

BUG: KASAN: slab-use-after-free in lecdattach net/atm/lec.c:751 [inline] BUG: KASAN: slab-use-after-free in laneioctl+0x2224/0x23e0 net/atm/lec.c:1008 Read of size 8 at addr ffff88807c7b8e68 by task syz.1.17/6142

CPU: 1 UID: 0 PID: 6142 Comm: syz.1.17 Not tainted 6.16.0-rc1-syzkaller-00239-g08215f5486ec #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Call Trace: <TASK> dumpstack lib/dumpstack.c:94 [inline] dumpstacklvl+0x116/0x1f0 lib/dumpstack.c:120 printaddressdescription mm/kasan/report.c:408 [inline] printreport+0xcd/0x680 mm/kasan/report.c:521 kasanreport+0xe0/0x110 mm/kasan/report.c:634 lecdattach net/atm/lec.c:751 [inline] laneioctl+0x2224/0x23e0 net/atm/lec.c:1008 dovccioctl+0x12c/0x930 net/atm/ioctl.c:159 sockdoioctl+0x118/0x280 net/socket.c:1190 sockioctl+0x227/0x6b0 net/socket.c:1311 vfsioctl fs/ioctl.c:51 [inline] dosysioctl fs/ioctl.c:907 [inline] sesysioctl fs/ioctl.c:893 [inline] x64sysioctl+0x18e/0x210 fs/ioctl.c:893 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xcd/0x4c0 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f </TASK>

Allocated by task 6132: kasansavestack+0x33/0x60 mm/kasan/common.c:47 kasansavetrack+0x14/0x30 mm/kasan/common.c:68 poisonkmallocredzone mm/kasan/common.c:377 [inline] kasankmalloc+0xaa/0xb0 mm/kasan/common.c:394 kasankmalloc include/linux/kasan.h:260 [inline] dokmallocnode mm/slub.c:4328 [inline] kvmallocnodenoprof+0x27b/0x620 mm/slub.c:5015 allocnetdevmqs+0xd2/0x1570 net/core/dev.c:11711 lecdattach net/atm/lec.c:737 [inline] laneioctl+0x17db/0x23e0 net/atm/lec.c:1008 dovccioctl+0x12c/0x930 net/atm/ioctl.c:159 sockdoioctl+0x118/0x280 net/socket.c:1190 sockioctl+0x227/0x6b0 net/socket.c:1311 vfsioctl fs/ioctl.c:51 [inline] dosysioctl fs/ioctl.c:907 [inline] sesysioctl fs/ioctl.c:893 [inline] x64sysioctl+0x18e/0x210 fs/ioctl.c:893 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xcd/0x4c0 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f

Freed by task 6132: kasansavestack+0x33/0x60 mm/kasan/common.c:47 kasansavetrack+0x14/0x30 mm/kasan/common.c:68 kasansavefreeinfo+0x3b/0x60 mm/kasan/generic.c:576 poisonslabobject mm/kasan/common.c:247 [inline] kasanslabfree+0x51/0x70 mm/kasan/common.c:264 kasanslabfree include/linux/kasan.h:233 [inline] slabfreehook mm/slub.c:2381 [inline] slabfree mm/slub.c:4643 [inline] kfree+0x2b4/0x4d0 mm/slub.c:4842 freenetdev+0x6c5/0x910 net/core/dev.c:11892 lecdattach net/atm/lec.c:744 [inline] laneioctl+0x1ce8/0x23e0 net/atm/lec.c:1008 dovccioctl+0x12c/0x930 net/atm/ioctl.c:159 sockdoioctl+0x118/0x280 net/socket.c:1190 sockioctl+0x227/0x6b0 net/socket.c:1311 vfsioctl fs/ioctl.c:51 [inline] dosysioctl fs/ioctl.c:907 [inline] sesysioctl fs/ioctl.c:893 [inline] x64sysioctl+0x18e/0x210 fs/ioctl.c:893