Hi

When using Healer to fuzz the Linux kernel, KMSAN reported an
uninit-value in sc_check_events.
The bug was trigger when fault injection was enabled.
However, this report doesn't make sense to me, because I found that
scsi_execute_req will memset the provided sshdr (scsi_normalize_sense
-> memset) unconditionally.
It's possible that I misunderstood the call stack to the
sr_check_events, or that there's a bug in KMSAN, so I'm reporting this
bug to you to confirm what the problem is.

Here are the details:
commit:   4ebaab5fb428374552175aa39832abf5cedb916a
version:   Linux 5.12
git tree:    kmsan
kernel config and full log can be found in the attached file.

FAULT INJECTION LOG:
=====================================================
FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 0
CPU: 1 PID: 23380 Comm: executor Not tainted 5.12.0-rc6+ #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
Call Trace:
 dump_stack+0x1ff/0x275
 should_fail+0x8b0/0x9d0
 __should_failslab+0x1f4/0x290
 should_failslab+0x29/0x70
 __kmalloc+0xbc/0x560
 ? bio_kmalloc+0xc4/0x310
 ? kmsan_get_metadata+0x4f/0x180
 bio_kmalloc+0xc4/0x310
 ? kmsan_get_metadata+0x11d/0x180
 blk_rq_map_kern+0xa05/0x1310
 ? kmsan_get_shadow_origin_ptr+0x84/0xb0
 ? kmsan_get_metadata+0x11d/0x180
 ? kmsan_get_shadow_origin_ptr+0x84/0xb0
 ? __msan_metadata_ptr_for_store_4+0x13/0x20
 ? scsi_initialize_rq+0x94/0xe0
 __scsi_execute+0x307/0xb10
 sr_check_events+0x1f4/0x10b0
 ? kmsan_internal_unpoison_shadow+0x42/0x70
 ? kmsan_get_metadata+0x11d/0x180
 cdrom_check_events+0xb7/0x240
 ? kmsan_get_metadata+0x11d/0x180
 sr_block_check_events+0x450/0x740
 ? sr_block_compat_ioctl+0x410/0x410
 disk_check_events+0x15b/0x860
 ? kmsan_get_metadata+0x11d/0x180
 ? kmsan_get_shadow_origin_ptr+0x84/0xb0
 bdev_check_media_change+0x2f2/0x730
 sr_block_open+0x3ee/0x870
 ? sr_revalidate_disk+0x8e0/0x8e0
 __blkdev_get+0x50e/0x12a0
 ? kmsan_internal_set_origin+0x85/0xc0
 ? kmsan_internal_unpoison_shadow+0x42/0x70
 blkdev_get_by_dev+0x288/0xd40
 ? kmsan_get_metadata+0x11d/0x180
 blkdev_open+0x233/0x450
 ? block_ioctl+0x1c0/0x1c0
 do_dentry_open+0xf36/0x17b0
 vfs_open+0xaf/0xe0
 path_openat+0x4d57/0x5e10
 ? kmsan_get_shadow_origin_ptr+0x84/0xb0
 ? kmsan_get_shadow_origin_ptr+0x84/0xb0
 ? __msan_metadata_ptr_for_load_4+0x10/0x20
 ? slab_post_alloc_hook+0xdf/0xf90
 ? kstrtoull+0x70e/0x7f0
 ? kmsan_get_metadata+0x4f/0x180
 do_filp_open+0x2b8/0x710
 do_sys_openat2+0x222/0x770
 ? kmsan_get_metadata+0x4f/0x180
 ? kmsan_internal_set_origin+0x85/0xc0
 ? kmsan_get_metadata+0x4f/0x180
 __se_sys_openat+0x24c/0x2b0
 __x64_sys_openat+0x56/0x70
 do_syscall_64+0xa2/0x120
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x46a379
Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd6dde46c58 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 000000000078c080 RCX: 000000000046a379
RDX: 0000000090000000 RSI: 0000000020000000 RDI: ffffffffffffff9c
RBP: 00007fd6dde46c90 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000000 R14: 000000000078c080 R15: 00007ffdf27ef460

KMSAN REPORT:
BUG: KMSAN: uninit-value in sr_get_events drivers/scsi/sr.c:210 [inline]
BUG: KMSAN: uninit-value in sr_check_events+0x2cc/0x10b0 drivers/scsi/sr.c:246
CPU: 1 PID: 23380 Comm: syz-executor Not tainted 5.12.0-rc6+ #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x1ff/0x275 lib/dump_stack.c:120
 kmsan_report+0xfb/0x1e0 mm/kmsan/kmsan_report.c:118
 __msan_warning+0x5c/0xa0 mm/kmsan/kmsan_instr.c:197
 sr_get_events drivers/scsi/sr.c:210 [inline]
 sr_check_events+0x2cc/0x10b0 drivers/scsi/sr.c:246
 cdrom_update_events drivers/cdrom/cdrom.c:1484 [inline]
 cdrom_check_events+0xb7/0x240 drivers/cdrom/cdrom.c:1494
 sr_block_check_events+0x450/0x740 drivers/scsi/sr.c:652
 disk_check_events+0x15b/0x860 block/genhd.c:1715
 disk_clear_events block/genhd.c:1648 [inline]
 bdev_check_media_change+0x2f2/0x730 block/genhd.c:1679
 sr_block_open+0x3ee/0x870 drivers/scsi/sr.c:528
 __blkdev_get+0x50e/0x12a0 fs/block_dev.c:1306
 blkdev_get_by_dev+0x288/0xd40 fs/block_dev.c:1458
 blkdev_open+0x233/0x450 fs/block_dev.c:1555
 do_dentry_open+0xf36/0x17b0 fs/open.c:826
 vfs_open+0xaf/0xe0 fs/open.c:940
 do_open fs/namei.c:3365 [inline]
 path_openat+0x4d57/0x5e10 fs/namei.c:3498
 do_filp_open+0x2b8/0x710 fs/namei.c:3525
 do_sys_openat2+0x222/0x770 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_openat fs/open.c:1219 [inline]
 __se_sys_openat+0x24c/0x2b0 fs/open.c:1214
 __x64_sys_openat+0x56/0x70 fs/open.c:1214
 do_syscall_64+0xa2/0x120 arch/x86/entry/common.c:48
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x46a379
Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd6dde46c58 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 000000000078c080 RCX: 000000000046a379
RDX: 0000000090000000 RSI: 0000000020000000 RDI: ffffffffffffff9c
RBP: 00007fd6dde46c90 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000000 R14: 000000000078c080 R15: 00007ffdf27ef460
Local variable ----sshdr.i@sr_check_events created at:
 sr_get_events drivers/scsi/sr.c:205 [inline]
 sr_check_events+0x153/0x10b0 drivers/scsi/sr.c:246
 sr_get_events drivers/scsi/sr.c:205 [inline]
 sr_check_events+0x153/0x10b0 drivers/scsi/sr.c:246

The bug can be trigger by ONE SYSTEM CALL easily:
# {Threaded:false Collide:false Repeat:true RepeatTimes:0 Procs:1
Slowdown:1 Sandbox:none Fault:true FaultCall:0 FaultNth:3 Leak:false
NetInjection:true NetDevices:true NetReset:true Cgroups:true
BinfmtMisc:true CloseFDs:true KCSAN:false DevlinkPCI:true USB:true
VhciInjection:true Wifi:true IEEE802154:true Sysctl:true
UseTmpDir:true HandleSegv:true Repro:false Trace:false}

openat$sr(0xffffffffffffff9c, &(0x7f0000000000)='/dev/sr0\x00', 0x90000000, 0x0)

Using syz-execprog to execute the reproduction program directly:
 ./syz-execprog  -repeat 0 -procs 1 -slowdown 1 -fault_call 0
-fault_nth 3 -enable tun -enable netdev -enable resetnet -enable
cgroups -enable binfmt-misc -enable close_fds -enable devlinkpci
-enable usb -enable vhci -enable wifi -enable ieee802154 -enable
sysctl repro.prog