cmd->cmnd can be allocated/freed dynamically in case of T10_PI_TYPE2_PROTECTION,
so we should check it in scsi_show_rq() because this request may have
been freed already here, and cmd->cmnd has been set as null.
We choose to accept read-after-free and dump request data as far as possible.
This patch fixs the following kernel crash when dumping request via block's
debugfs interface:
[ 252.962045] BUG: unable to handle kernel NULL pointer dereference at
(null)
[ 252.963007] IP: scsi_format_opcode_name+0x1a/0x1c0
[ 252.963007] PGD 25e75a067 P4D 25e75a067 PUD 25e75b067 PMD 0
[ 252.963007] Oops: 0000 [#1] PREEMPT SMP
[ 252.963007] Dumping ftrace buffer:
[ 252.963007] (ftrace buffer empty)
[ 252.963007] Modules linked in: scsi_debug ebtable_filter ebtables
ip6table_filter ip6_tables xt_CHECKSUM iptable_mangle ipt_MASQUERADE
nf_nat_masquerade_ipv4 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4
nf_nat nf_conntrack libcrc32c bridge stp llc iptable_filter fuse ip_tables
sd_mod sg mptsas mptscsih mptbase crc32c_intel ahci libahci nvme serio_raw
scsi_transport_sas libata lpc_ich nvme_core virtio_scsi binfmt_misc dm_mod
iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi null_blk configs
[ 252.963007] CPU: 1 PID: 1881 Comm: cat Not tainted
4.14.0-rc2.blk_mq_io_hang+ #516
[ 252.963007] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
1.9.3-1.fc25 04/01/2014
[ 252.963007] task: ffff88025e6f6000 task.stack: ffffc90001bd0000
[ 252.963007] RIP: 0010:scsi_format_opcode_name+0x1a/0x1c0
[ 252.963007] RSP: 0018:ffffc90001bd3c50 EFLAGS: 00010286
[ 252.963007] RAX: 00000000ffff4843 RBX: 0000000000000050 RCX: 0000000000000000
[ 252.963007] RDX: 0000000000000000 RSI: 0000000000000050 RDI: ffffc90001bd3cd8
[ 252.963007] RBP: ffffc90001bd3c88 R08: 0000000000001000 R09: 0000000000000000
[ 252.963007] R10: ffff880275134000 R11: ffff88027513406c R12: 0000000000000050
[ 252.963007] R13: ffffc90001bd3cd8 R14: 0000000000000000 R15: 0000000000000000
[ 252.963007] FS: 00007f4d11762700(0000) GS:ffff88027fc40000(0000)
knlGS:0000000000000000
[ 252.963007] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 252.963007] CR2: 0000000000000000 CR3: 000000025e789003 CR4: 00000000003606e0
[ 252.963007] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 252.963007] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 252.963007] Call Trace:
[ 252.963007] __scsi_format_command+0x27/0xc0
[ 252.963007] scsi_show_rq+0x5c/0xc0
[ 252.963007] ? seq_printf+0x4e/0x70
[ 252.963007] ? blk_flags_show+0x5b/0xf0
[ 252.963007] __blk_mq_debugfs_rq_show+0x116/0x130
[ 252.963007] blk_mq_debugfs_rq_show+0xe/0x10
[ 252.963007] seq_read+0xfe/0x3b0
[ 252.963007] ? __handle_mm_fault+0x631/0x1150
[ 252.963007] full_proxy_read+0x54/0x90
[ 252.963007] __vfs_read+0x37/0x160
[ 252.963007] ? security_file_permission+0x9b/0xc0
[ 252.963007] vfs_read+0x96/0x130
[ 252.963007] SyS_read+0x55/0xc0
[ 252.963007] entry_SYSCALL_64_fastpath+0x1a/0xa5
[ 252.963007] RIP: 0033:0x7f4d1127e9b0
[ 252.963007] RSP: 002b:00007ffd27082568 EFLAGS: 00000246 ORIG_RAX:
0000000000000000
[ 252.963007] RAX: ffffffffffffffda RBX: 00007f4d1154bb20 RCX: 00007f4d1127e9b0
[ 252.963007] RDX: 0000000000020000 RSI: 00007f4d115a7000 RDI: 0000000000000003
[ 252.963007] RBP: 0000000000021010 R08: ffffffffffffffff R09: 0000000000000000
[ 252.963007] R10: 000000000000037b R11: 0000000000000246 R12: 0000000000022000
[ 252.963007] R13: 00007f4d1154bb78 R14: 0000000000001000 R15: 0000000000020000
[ 252.963007] Code: c6 e8 1b ca 24 00 eb 8c e8 74 2c ae ff 0f 1f 40 00 0f 1f
44 00 00 55 48 89 e5 41 56 41 55 41 54 53 49 89 fd 49 89 f4 48 83 ec 18 <44> 0f
b6 32 48 c7 45 c8 00 00 00 00 65 48 8b 04 25 28 00 00 00
[ 252.963007] RIP: scsi_format_opcode_name+0x1a/0x1c0 RSP: ffffc90001bd3c50
[ 252.963007] CR2: 0000000000000000
[ 252.963007] ---[ end trace 83c5bddfbaa6573c ]---
[ 252.963007] Kernel panic - not syncing: Fatal exception
[ 252.963007] Dumping ftrace buffer:
[ 252.963007] (ftrace buffer empty)
[ 252.963007] Kernel Offset: disabled
[ 252.963007] ---[ end Kernel panic - not syncing: Fatal exception
Fixes: 0eebd005dd07(scsi: Implement blk_mq_ops.show_rq())
Cc: Bart Van Assche <bart.vanass...@sandisk.com>
Cc: Omar Sandoval <osan...@fb.com>
Cc: Martin K. Petersen <martin.peter...@oracle.com>
Cc: James Bottomley <james.bottom...@hansenpartnership.com>
Cc: Hannes Reinecke <h...@suse.com>
Signed-off-by: Ming Lei <ming....@redhat.com>
---
V2:
- fix typo
V3:
- prefer to dump data and accept read-after-free
- add some comment
V4:
- read the two variable into local variable first, for avoiding
free between check and passing to __scsi_format_command().
drivers/scsi/scsi_debugfs.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/drivers/scsi/scsi_debugfs.c b/drivers/scsi/scsi_debugfs.c
index 5e9755008aed..f8437c456458 100644
--- a/drivers/scsi/scsi_debugfs.c
+++ b/drivers/scsi/scsi_debugfs.c
@@ -8,8 +8,20 @@ void scsi_show_rq(struct seq_file *m, struct request *rq)
struct scsi_cmnd *cmd = container_of(scsi_req(rq), typeof(*cmd), req);
int msecs = jiffies_to_msecs(jiffies - cmd->jiffies_at_alloc);
char buf[80];
+ unsigned char *cdb = cmd->cmnd;
+ unsigned short cdb_len = cmd->cmd_len;
- __scsi_format_command(buf, sizeof(buf), cmd->cmnd, cmd->cmd_len);
+ /*
+ * This rq may have been freed, so don't be surprised if
+ * read-after-free is reported.
+ *
+ * __scsi_format_command() should be written as not being broken
+ * with gargabe 'cdb' input.
+ */
+ if (cdb && cdb_len)
+ __scsi_format_command(buf, sizeof(buf), cdb, cdb_len);
+ else
+ strcpy(buf, "");
seq_printf(m, ", .cmd=%s, .retries=%d, allocated %d.%03d s ago", buf,
cmd->retries, msecs / 1000, msecs % 1000);
}
--
2.9.5
