| Message ID | 1510156868.3121.7.camel@HansenPartnership.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Nov 08, 2017 at 08:01:08AM -0800, James Bottomley wrote: > On Wed, 2017-11-08 at 21:21 +0800, Ming Lei wrote: > > 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 in scsi_show_rq(). > > > > 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.vanassche@sandisk.com> > > Cc: Omar Sandoval <osandov@fb.com> > > Cc: Martin K. Petersen <martin.petersen@oracle.com> > > Cc: James Bottomley <James.Bottomley@HansenPartnership.com> > > Cc: Hannes Reinecke <hare@suse.com> > > Signed-off-by: Ming Lei <ming.lei@redhat.com> > > --- > > V2: > > - fix typo > > V3: > > - prefer to dump data and accept read-after-free > > - add some comment > > > > James, since read-after-free is inevitable and we prefer to dump > > data, > > we needn't to move clearing the buffer pointer before freeing the > > buffer > > in sd_uninit_command(), otherwise we may miss the dump a bit > > > > drivers/scsi/scsi_debugfs.c | 12 +++++++++++- > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/scsi/scsi_debugfs.c > > b/drivers/scsi/scsi_debugfs.c > > index 5e9755008aed..2320d8f569b8 100644 > > --- a/drivers/scsi/scsi_debugfs.c > > +++ b/drivers/scsi/scsi_debugfs.c > > @@ -9,7 +9,17 @@ void scsi_show_rq(struct seq_file *m, struct request > > *rq) > > int msecs = jiffies_to_msecs(jiffies - cmd- > > >jiffies_at_alloc); > > char buf[80]; > > > > - __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. > > This can be fixed, see below. > > > + * > > + * __scsi_format_command() should be written as not being > > broken > > + * with gargabe 'cdb' input. > > + */ > > + if (cmd->cmnd && cmd->cmd_len) > > Why is it necessary to check cmd_len as well? It's not wrong, it just > doesn't seem to be useful If cmd->cmd_len is 0, the 'buf' won't be initialized by __scsi_format_command(). > > > + __scsi_format_command(buf, sizeof(buf), cmd->cmnd, > > cmd->cmd_len); > > + else > > + strcpy(buf, ""); > > seq_printf(m, ", .cmd=%s, .retries=%d, allocated %d.%03d s > > ago", buf, > > cmd->retries, msecs / 1000, msecs % 1000); > > } > > > This is what you need as well: > > diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c > index d175c5c5ccf8..2d5e918c3e75 100644 > --- a/drivers/scsi/sd.c > +++ b/drivers/scsi/sd.c > @@ -1284,6 +1284,7 @@ static int sd_init_command(struct scsi_cmnd *cmd) > static void sd_uninit_command(struct scsi_cmnd *SCpnt) > { > struct request *rq = SCpnt->request; > + unsigned char *cmnd = SCpnt->cmnd; > > if (SCpnt->flags & SCMD_ZONE_WRITE_LOCK) > sd_zbc_write_unlock_zone(SCpnt); > @@ -1292,9 +1293,9 @@ static void sd_uninit_command(struct scsi_cmnd *SCpnt) > __free_page(rq->special_vec.bv_page); > > if (SCpnt->cmnd != scsi_req(rq)->cmd) { > - mempool_free(SCpnt->cmnd, sd_cdb_pool); > SCpnt->cmnd = NULL; > SCpnt->cmd_len = 0; > + mempool_free(cmnd, sd_cdb_pool); > } > } > > > The reason it works is that function calls are an absolute barrier, so > setting the cmnd to NULL is seen everywhere before the mempool_free() > starts and the execution path of mempool_free() is much longer > than _scsi_format_command() so you can never get a use after free in > practice. To make this completely bullet proof, scsi_show_rq() should Yeah, that is true, but still can't avoid use-after-free since preemption or interrupt may change the timing a lot. Especially sd_uninit_command() is run in interrupt context. > take a copy of the cmnd pointer before testing and using it, otherwise > there's a minute window where it could go to NULL between the check and > __scsi_format_command(). I've forgotten if we can rely on no- > preemption for RT or we need to add it explicitly, but I'm sure you can > figure it out. If we set SCpnt->cmnd as NULL earlier, we may miss the command data with more possibility, that seems what we want to avoid too from debug function view.
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index d175c5c5ccf8..2d5e918c3e75 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -1284,6 +1284,7 @@ static int sd_init_command(struct scsi_cmnd *cmd) static void sd_uninit_command(struct scsi_cmnd *SCpnt) { struct request *rq = SCpnt->request; + unsigned char *cmnd = SCpnt->cmnd; if (SCpnt->flags & SCMD_ZONE_WRITE_LOCK) sd_zbc_write_unlock_zone(SCpnt); @@ -1292,9 +1293,9 @@ static void sd_uninit_command(struct scsi_cmnd *SCpnt) __free_page(rq->special_vec.bv_page); if (SCpnt->cmnd != scsi_req(rq)->cmd) { - mempool_free(SCpnt->cmnd, sd_cdb_pool); SCpnt->cmnd = NULL; SCpnt->cmd_len = 0; + mempool_free(cmnd, sd_cdb_pool); } }