CVE-2025-68776: net/hsr: fix NULL pointer dereference in prp_get_untagged_frame()

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

net/hsr: fix NULL pointer dereference in prpgetuntaggedframe()

prpgetuntaggedframe() calls pskbcopy() to create frame->skbstd but doesn't check if the allocation failed. If pskbcopy() returns NULL, skbclone() is called with a NULL pointer, causing a crash:

Oops: general protection fault, probably for non-canonical address 0xdffffc000000000f: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000078-0x000000000000007f] CPU: 0 UID: 0 PID: 5625 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:skbclone+0xd7/0x3a0 net/core/skbuff.c:2041 Code: 03 42 80 3c 20 00 74 08 4c 89 f7 e8 23 29 05 f9 49 83 3e 00 0f 85 a0 01 00 00 e8 94 dd 9d f8 48 8d 6b 7e 49 89 ee 49 c1 ee 03 <43> 0f b6 04 26 84 c0 0f 85 d1 01 00 00 44 0f b6 7d 00 41 83 e7 0c RSP: 0018:ffffc9000d00f200 EFLAGS: 00010207 RAX: ffffffff892235a1 RBX: 0000000000000000 RCX: ffff88803372a480 RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000000 RBP: 000000000000007e R08: ffffffff8f7d0f77 R09: 1ffffffff1efa1ee R10: dffffc0000000000 R11: fffffbfff1efa1ef R12: dffffc0000000000 R13: 0000000000000820 R14: 000000000000000f R15: ffff88805144cc00 FS: 0000555557f6d500(0000) GS:ffff88808d72f000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000555581d35808 CR3: 000000005040e000 CR4: 0000000000352ef0 Call Trace: <TASK> hsrforwarddo net/hsr/hsrforward.c:-1 [inline] hsrforwardskb+0x1013/0x2860 net/hsr/hsrforward.c:741 hsrhandleframe+0x6ce/0xa70 net/hsr/hsrslave.c:84 netifreceiveskbcore+0x10b9/0x4380 net/core/dev.c:5966 netifreceiveskbonecore net/core/dev.c:6077 [inline] netifreceiveskb+0x72/0x380 net/core/dev.c:6192 netifreceiveskbinternal net/core/dev.c:6278 [inline] netifreceiveskb+0x1cb/0x790 net/core/dev.c:6337 tunrxbatched+0x1b9/0x730 drivers/net/tun.c:1485 tungetuser+0x2b65/0x3e90 drivers/net/tun.c:1953 tunchrwriteiter+0x113/0x200 drivers/net/tun.c:1999 newsyncwrite fs/readwrite.c:593 [inline] vfswrite+0x5c9/0xb30 fs/readwrite.c:686 ksyswrite+0x145/0x250 fs/readwrite.c:738 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xfa/0xfa0 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f RIP: 0033:0x7f0449f8e1ff Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 f9 92 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 4c 93 02 00 48 RSP: 002b:00007ffd7ad94c90 EFLAGS: 00000293 ORIGRAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f044a1e5fa0 RCX: 00007f0449f8e1ff RDX: 000000000000003e RSI: 0000200000000500 RDI: 00000000000000c8 RBP: 00007ffd7ad94d20 R08: 0000000000000000 R09: 0000000000000000 R10: 000000000000003e R11: 0000000000000293 R12: 0000000000000001 R13: 00007f044a1e5fa0 R14: 00007f044a1e5fa0 R15: 0000000000000003 </TASK>

Add a NULL check immediately after pskbcopy() to handle allocation failures gracefully.