CVE-2025-40064

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

smc: Fix use-after-free in _pnetfindbasendev().

syzbot reported use-after-free of netdevice in _pnetfindbase_ndev(), which was called during connect(). [0]

smcpnetfindismresource() fetches skdstget(sk)->dev and passes down to pnetfindbasendev(), where RTNL is held. Then, UAF happened at _pnetfindbase_ndev() when the dev is first used.

This means dev had already been freed before acquiring RTNL in pnetfindbase_ndev().

While dev is going away, dst->dev could be swapped with blackhole_netdev, and the dev's refcnt by dst will be released.

We must hold dev's refcnt before calling smcpnetfindismresource().

Also, smcpnetfindroceresource() has the same problem.

Let's use _skdstget() and dstdev_rcu() in the two functions.

Read of size 1 at addr ffff888036bac33a by task syz.0.3632/18609

CPU: 1 UID: 0 PID: 18609 Comm: syz.0.3632 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 Call Trace: <TASK> dumpstacklvl+0x189/0x250 lib/dumpstack.c:120 printaddressdescription mm/kasan/report.c:378 [inline] printreport+0xca/0x240 mm/kasan/report.c:482 kasanreport+0x118/0x150 mm/kasan/report.c:595 _pnetfindbasendev+0x1b1/0x1c0 net/smc/smcpnet.c:926 pnetfindbasendev net/smc/smcpnet.c:946 [inline] smcpnetfindismbypnetid net/smc/smcpnet.c:1103 [inline] smcpnetfindismresource+0xef/0x390 net/smc/smcpnet.c:1154 smcfindismdevice net/smc/afsmc.c:1030 [inline] smcfindproposaldevices net/smc/afsmc.c:1115 [inline] _smcconnect+0x372/0x1890 net/smc/afsmc.c:1545 smcconnect+0x877/0xd90 net/smc/afsmc.c:1715 _sysconnectfile net/socket.c:2086 [inline] _sysconnect+0x313/0x440 net/socket.c:2105 _dosysconnect net/socket.c:2111 [inline] _sesysconnect net/socket.c:2108 [inline] _x64sysconnect+0x7a/0x90 net/socket.c:2108 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xfa/0x3b0 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f RIP: 0033:0x7f47cbf8eba9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f47ccdb1038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a RAX: ffffffffffffffda RBX: 00007f47cc1d5fa0 RCX: 00007f47cbf8eba9 RDX: 0000000000000010 RSI: 0000200000000280 RDI: 000000000000000b RBP: 00007f47cc011e19 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f47cc1d6038 R14: 00007f47cc1d5fa0 R15: 00007ffc512f8aa8 </TASK>

The buggy address belongs to the physical page: page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888036bacd00 pfn:0x36bac flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff) raw: 00fff00000000000 ffffea0001243d08 ffff8880b863fdc0 0000000000000000 raw: ffff888036bacd00 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: kasan: bad access detected pageowner tracks the page as freed page last allocated via order 2, migratetype Unmovable, gfpmask 0x446dc0(GFPKERNELACCOUNT|GFPZERO|GFPNOWARN|GFPRETRYMAYFAIL|GFPCOMP), pid 16741, tgid 16741 (syz-executor), ts 343313197788, freets 380670750466 setpageowner include/linux/pageowner.h:32 [inline] postallochook+0x240/0x2a0 mm/pagealloc.c:1851 prepnewpage mm/pagealloc.c:1859 [inline] getpagefromfreelist+0x21e4/0x22c0 mm/pagealloc.c:3858 allocfrozenpagesnoprof+0x181/0x370 mm/pagealloc.c:5148 allocpagesmpol+0x232/0x4a0 mm/mempolicy.c:2416 _kmalloclargenode+0x5f/0x1b0 mm/slub.c:4317 _kmalloclargenodenoprof+0x18/0x90 mm/slub.c:4348 _dokmallocnode mm/slub.c:4364 [inline] _kvmallocnode ---truncated---