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From:   Tadeusz Struk <tadeusz.struk@linaro.org>
To:     linux-scsi@vger.kernel.org
Cc:     Tadeusz Struk <tadeusz.struk@linaro.org>,
        Christoph Hellwig <hch@lst.de>,
        "James E . J . Bottomley" <jejb@linux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        syzbot+5516b30f5401d4dcbcae@syzkaller.appspotmail.com
Subject: [PATCH] scsi: core: initialize cmd->cmnd before it is used
Date:   Mon,  1 Nov 2021 12:24:17 -0700
Message-Id: <20211101192417.324799-1-tadeusz.struk@linaro.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The scsi_setup_scsi_cmnd() function initializes the cmd->cmnd command
field, but in case the cmd_len is zero the field is used to detect
the command size before it is initialized. This triggers null-ptr-deref
as in the trace below. Fix this by setting cmd->cmnd earlier.

[   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: Christoph Hellwig <hch@lst.de>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: <linux-scsi@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Cc: <stable@vger.kernel.org> # 5.15, 5.14, 5.10
Fixes: 2ceda20f0a99a74a82b78870f3b3e5fa93087a7f
Reported-by: syzbot+5516b30f5401d4dcbcae@syzkaller.appspotmail.com
Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
---
 drivers/scsi/scsi_lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 572673873ddf..cd4b57747448 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1173,10 +1173,10 @@ static blk_status_t scsi_setup_scsi_cmnd(struct scsi_device *sdev,
 		memset(&cmd->sdb, 0, sizeof(cmd->sdb));
 	}
 
+	cmd->cmnd = scsi_req(req)->cmd;
 	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;
 	return BLK_STS_OK;
-- 
2.31.1