Hi, all Recently, our syzbot test reported NULL pointer dereference in device_del() by injecting memory allocation fail in device_add() invoking from register_disk(), as following: general protection fault, probably for non-canonical address 0xdffffc0000000021: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f] CPU: 0 PID: 9441 Comm: syz-executor348 Tainted: G W 5.10.0+ #6 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 RIP: 0010:kill_device+0x9b/0x160 drivers/base/core.c:3050 Code: fd 49 83 c6 48 4c 89 f3 48 c1 eb 03 42 80 3c 3b 00 74 08 4c 89 f7 e8 94 ef 8c fd bd 08 01 00 00 49 03 2e 48 89 e8 48 c1 e8 03 <42> 8a 04 38 84 c0 0f 85 89 00 00 00 0f b6 6d 00 83 e5 01 31 ff 89 RSP: 0018:ffffc900032bfd38 EFLAGS: 00010206 RAX: 0000000000000021 RBX: 1ffff1100299b816 RCX: ffff8881115cc200 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005 RBP: 0000000000000108 R08: dffffc0000000000 R09: ffff8881115cc200 R10: ffffed100299b830 R11: 0000000000000000 R12: dffffc0000000000 R13: 0000000000000008 R14: ffff888014cdc0b0 R15: dffffc0000000000 FS: 0000000000e29880(0000) GS:ffff888061000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000006cc098 CR3: 0000000018764000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: device_del+0x62/0xa00 drivers/base/core.c:3078 del_gendisk+0x725/0x880 block/genhd.c:952 loop_remove+0x42/0xa0 drivers/block/loop.c:2193 loop_control_ioctl+0x31d/0x3a0 drivers/block/loop.c:2292 vfs_ioctl+0xa2/0xf0 fs/ioctl.c:48 __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl fs/ioctl.c:739 [inline] __x64_sys_ioctl+0xfe/0x140 fs/ioctl.c:739 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9 When device_add() fail caused by some memory allocation fail, it will free 'dev->p' and set the pointer as NULL. Since add_disk() will ignore the functions fail and go on working, it will cause various NULL pointer dereference in del_gendisk(), including 'dev->p' is NULL in kill_device() from device_del(), 'name' is NULL in sysfs_remove_link() from del_gendisk(), kobj->sd is 'NULL' when call dpm_sysfs_remove() from device_del(), and so on. I try to fix the the problem by passing device_del() when device_add() fail[1], which is is not complete. And Greg thinks we should fix up users of device_del(). My question is do we need to check return value of register_disk() and fail __device_add_disk() when functions in it fail. Is there some historical reason that let us ignore various fail from __device_add_disk() and register_disk()? [1] https://lore.kernel.org/linux-block/20210401130138.2164928-1-yuyufen@xxxxxxxxxx/ Thanks, Yufen
