CVE-2024-26957: s390/zcrypt: fix reference counting on zcrypt card objects

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

s390/zcrypt: fix reference counting on zcrypt card objects

Tests with hot-plugging crytpo cards on KVM guests with debug kernel build revealed an use after free for the load field of the struct zcryptcard. The reason was an incorrect reference handling of the zcrypt card object which could lead to a free of the zcrypt card object while it was still in use.

This is an example of the slab message:

kernel: 0x00000000885a7512-0x00000000885a7513 @offset=1298. First byte 0x68 instead of 0x6b kernel: Allocated in zcryptcardalloc+0x36/0x70 [zcrypt] age=18046 cpu=3 pid=43 kernel: kmalloctrace+0x3f2/0x470 kernel: zcryptcardalloc+0x36/0x70 [zcrypt] kernel: zcryptcex4cardprobe+0x26/0x380 [zcryptcex4] kernel: apdeviceprobe+0x15c/0x290 kernel: reallyprobe+0xd2/0x468 kernel: driverprobedevice+0x40/0xf0 kernel: deviceattachdriver+0xc0/0x140 kernel: busforeachdrv+0x8c/0xd0 kernel: deviceattach+0x114/0x198 kernel: busprobedevice+0xb4/0xc8 kernel: deviceadd+0x4d2/0x6e0 kernel: apscanadapter+0x3d0/0x7c0 kernel: apscanbus+0x5a/0x3b0 kernel: apscanbuswqcallback+0x40/0x60 kernel: processonework+0x26e/0x620 kernel: workerthread+0x21c/0x440 kernel: Freed in zcryptcardput+0x54/0x80 [zcrypt] age=9024 cpu=3 pid=43 kernel: kfree+0x37e/0x418 kernel: zcryptcardput+0x54/0x80 [zcrypt] kernel: apdeviceremove+0x4c/0xe0 kernel: devicereleasedriverinternal+0x1c4/0x270 kernel: busremovedevice+0x100/0x188 kernel: devicedel+0x164/0x3c0 kernel: deviceunregister+0x30/0x90 kernel: apscanadapter+0xc8/0x7c0 kernel: apscanbus+0x5a/0x3b0 kernel: apscanbuswqcallback+0x40/0x60 kernel: processonework+0x26e/0x620 kernel: workerthread+0x21c/0x440 kernel: kthread+0x150/0x168 kernel: retfromfork+0x3c/0x58 kernel: retfromfork+0xa/0x30 kernel: Slab 0x00000372022169c0 objects=20 used=18 fp=0x00000000885a7c88 flags=0x3ffff00000000a00(workingset|slab|node=0|zone=1|lastcpupid=0x1ffff) kernel: Object 0x00000000885a74b8 @offset=1208 fp=0x00000000885a7c88 kernel: Redzone 00000000885a74b0: bb bb bb bb bb bb bb bb ........ kernel: Object 00000000885a74b8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk kernel: Object 00000000885a74c8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk kernel: Object 00000000885a74d8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk kernel: Object 00000000885a74e8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk kernel: Object 00000000885a74f8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk kernel: Object 00000000885a7508: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 68 4b 6b 6b 6b a5 kkkkkkkkkkhKkkk. kernel: Redzone 00000000885a7518: bb bb bb bb bb bb bb bb ........ kernel: Padding 00000000885a756c: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZ kernel: CPU: 0 PID: 387 Comm: systemd-udevd Not tainted 6.8.0-HF #2 kernel: Hardware name: IBM 3931 A01 704 (KVM/Linux) kernel: Call Trace: kernel: [<00000000ca5ab5b8>] dumpstacklvl+0x90/0x120 kernel: [<00000000c99d78bc>] checkbytesandreport+0x114/0x140 kernel: [<00000000c99d53cc>] checkobject+0x334/0x3f8 kernel: [<00000000c99d820c>] allocdebugprocessing+0xc4/0x1f8 kernel: [<00000000c99d852e>] getpartialnode.part.0+0x1ee/0x3e0 kernel: [<00000000c99d94ec>] slaballoc+0xaf4/0x13c8 kernel: [<00000000c99d9e38>] slaballoc.constprop.0+0x78/0xb8 kernel: [<00000000c99dc8dc>] kmalloc+0x434/0x590 kernel: [<00000000c9b4c0ce>] ext4htreestoredirent+0x4e/0x1c0 kernel: [<00000000c9b908a2>] htreedirblocktotree+0x17a/0x3f0 kernel: ---truncated---