[PATCH 2/2] scsi: core: remove command size deduction from scsi_setup_scsi_cmnd

From: Tadeusz Struk
Date: Tue Nov 02 2021 - 20:37:52 EST

No need to deduce command size in scsi_setup_scsi_cmnd() anymore
as appropriate checks have been added to scsi_fill_sghdr_rq() function
and the cmd_len should never be zero here.
The code to do that wasn't correct anyway, as it used uninitialized
cmd->cmnd, which caused a null-ptr-deref if the command size was zero
as in the trace below. Fix this by removing the uneeded code.

[ 21.105583][ T1822] KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
[ 21.106749][ T1822] CPU: 0 PID: 1822 Comm: repro Not tainted 5.15.0 #1
[ 21.107678][ T1822] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
[ 21.109004][ T1822] RIP: 0010:scsi_queue_rq+0xf09/0x2180
[ 21.112499][ T1822] RSP: 0018:ffffc90000d0f098 EFLAGS: 00010246
[ 21.113347][ T1822] RAX: dffffc0000000000 RBX: ffff888107b0d408 RCX: 0000000000000000
[ 21.114448][ T1822] RDX: ffff888107168000 RSI: 0000000000000000 RDI: 0000000000000000
[ 21.115553][ T1822] RBP: ffffc90000d0f150 R08: ffffffff82a96d37 R09: ffff888107b0d410
[ 21.116683][ T1822] R10: ffffed1020f61a85 R11: 0000000000000000 R12: 1ffff11020f61a7f
[ 21.117793][ T1822] R13: 0000000000000000 R14: 0000000000000000 R15: ffff888107b0d3fc
[ 21.118894][ T1822] FS: 00007f5bfac9f640(0000) GS:ffff88811b200000(0000) knlGS:0000000000000000
[ 21.120132][ T1822] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 21.121050][ T1822] CR2: 0000000020001000 CR3: 0000000109acb000 CR4: 0000000000150eb0
[ 21.123125][ T1822] Call Trace:
[ 21.124020][ T1822] blk_mq_dispatch_rq_list+0x7c7/0x12d0
[ 21.125486][ T1822] ? __kasan_check_write+0x14/0x20
[ 21.126794][ T1822] ? do_raw_spin_lock+0x9a/0x230
[ 21.128023][ T1822] ? blk_mq_get_driver_tag+0x920/0x920
[ 21.129345][ T1822] __blk_mq_sched_dispatch_requests+0x244/0x380
[ 21.130826][ T1822] ? blk_mq_sched_dispatch_requests+0x160/0x160
[ 21.132241][ T1822] ? _find_next_bit+0x1ec/0x210
[ 21.133376][ T1822] blk_mq_sched_dispatch_requests+0xf0/0x160
[ 21.134724][ T1822] __blk_mq_run_hw_queue+0xe8/0x160
[ 21.135878][ T1822] ? __list_splice+0x100/0x100
[ 21.136902][ T1822] __blk_mq_delay_run_hw_queue+0x252/0x5d0
[ 21.138115][ T1822] blk_mq_run_hw_queue+0x1dd/0x3b0
[ 21.139184][ T1822] ? blk_mq_dispatch_rq_list+0x12d0/0x12d0
[ 21.140322][ T1822] ? _raw_spin_unlock+0x13/0x30
[ 21.141273][ T1822] ? blk_mq_request_bypass_insert+0xcf/0xe0
[ 21.142414][ T1822] blk_mq_sched_insert_request+0x1ff/0x3e0
[ 21.143531][ T1822] ? timekeeping_get_ns+0xb1/0xc0
[ 21.144462][ T1822] ? blk_mq_sched_try_insert_merge+0x240/0x240
[ 21.145592][ T1822] ? update_io_ticks+0x17c/0x190
[ 21.146472][ T1822] ? blk_account_io_start+0x21c/0x260
[ 21.147421][ T1822] blk_execute_rq_nowait+0x173/0x1e0
[ 21.148356][ T1822] ? blk_execute_rq+0x540/0x540
[ 21.149247][ T1822] ? asan.module_ctor+0x10/0x10
[ 21.150066][ T1822] blk_execute_rq+0x15c/0x540
[ 21.150869][ T1822] ? cap_capable+0x2ca/0x330
[ 21.151653][ T1822] ? blk_execute_rq_nowait+0x1e0/0x1e0
[ 21.152539][ T1822] ? ns_capable_common+0x8f/0xf0
[ 21.153348][ T1822] ? capable+0x1c/0x20
[ 21.153984][ T1822] sg_io+0x97c/0x1370
[ 21.154614][ T1822] ? scsi_ioctl_block_when_processing_errors+0x1e0/0x1e0
[ 21.155712][ T1822] ? in_compat_syscall+0xd0/0xd0
[ 21.156488][ T1822] ? futex_wait+0x4fb/0x640
[ 21.157175][ T1822] scsi_ioctl+0xe16/0x28e0
[ 21.157836][ T1822] ? __kasan_check_read+0x11/0x20
[ 21.158596][ T1822] ? get_sg_io_hdr+0x10a0/0x10a0
[ 21.159347][ T1822] ? __fsnotify_parent+0x4ee/0x710
[ 21.160111][ T1822] ? do_futex+0x3f2/0x1030
[ 21.160764][ T1822] ? futex_exit_release+0x70/0x70
[ 21.161494][ T1822] ? do_vfs_ioctl+0xafa/0x1af0
[ 21.162168][ T1822] ? scsi_host_in_recovery+0xb9/0x160
[ 21.162921][ T1822] ? vfs_write+0x397/0x580
[ 21.163547][ T1822] ? scsi_ioctl_block_when_processing_errors+0xae/0x1e0
[ 21.164521][ T1822] sd_ioctl+0x134/0x170
[ 21.165087][ T1822] blkdev_ioctl+0x362/0x6e0
[ 21.165724][ T1822] ? blkdev_compat_ptr_ioctl+0xf0/0xf0
[ 21.166470][ T1822] ? fput_many+0x5e/0x1d0
[ 21.167059][ T1822] ? __restore_fpregs_from_fpstate+0xb5/0x160
[ 21.167873][ T1822] block_ioctl+0xb0/0xf0
[ 21.168437][ T1822] vfs_ioctl+0xa7/0xf0
[ 21.168970][ T1822] __x64_sys_ioctl+0x10d/0x150
[ 21.169602][ T1822] do_syscall_64+0x3d/0xb0
[ 21.170176][ T1822] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 21.180158][ T1822] ---[ end trace 8b086e334adef6d2 ]---
[ 21.191043][ T1822] Kernel panic - not syncing: Fatal exception
[ 21.191728][ T1822] Kernel Offset: disabled

Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: James E.J. Bottomley <jejb@xxxxxxxxxxxxx>
Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Cc: <linux-scsi@xxxxxxxxxxxxxxx>
Cc: <linux-kernel@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 5.15, 5.14, 5.10
Fixes: 2ceda20f0a99a74a82b78870f3b3e5fa93087a7f
Reported-by: syzbot+5516b30f5401d4dcbcae@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Tadeusz Struk <tadeusz.struk@xxxxxxxxxx>
---
drivers/scsi/scsi_lib.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 572673873ddf..e026da7549be 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1174,8 +1174,6 @@ static blk_status_t scsi_setup_scsi_cmnd(struct scsi_device *sdev,
}

cmd->cmd_len = scsi_req(req)->cmd_len;
- if (cmd->cmd_len == 0)
- cmd->cmd_len = scsi_command_size(cmd->cmnd);
cmd->cmnd = scsi_req(req)->cmd;
cmd->transfersize = blk_rq_bytes(req);
cmd->allowed = scsi_req(req)->retries;
--
2.31.1