scsi_host_alloc does not check for used shost->host_no

scsi_host_alloc does not check for used shost->host_no

[Daniel Debonzi]

[-- Attachment #1: Type: text/plain, Size: 1173 bytes --]

Hi everyone,

First of all, it is the first time I am sending something to one of the 
kernel mail lists. So, if it is not the right place for that, if it is 
not the only place for that, or I am doing something wrong, or wherever, 
please, just let me know.

After a good time investigating why modprobe/rmmod pata_pdc2027x lots of 
times was driven to a kernel panic I found out that the problem was on 
scsi host layer (if I can call it like this).

In a brief explanation, every time a scsi host is allocated a shost 
structure get an host_no attribute assigned an as far as I can see it 
should be unique. The point is that this host_no value comes from a 
variable that is incremented every time a scsi host is allocated and in 
a first moment, we will not have two shost structs with the same 
host_no. But for instance, when this always incremented variable 
overflows, it does not work anymore and it can happen to have to 
different shost structures with the same host_no.

I made a patch that solves the problem in a very simple way, but I don't 
know how acceptable it is. I am sending it in attachment and any 
feedback will be welcome.

Thanks
Daniel Debonzi

[-- Attachment #2: scsi_host_no_verify.diff --]
[-- Type: text/x-diff, Size: 1047 bytes --]

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index c6457bf..2e191f4 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -310,7 +310,7 @@ struct device_type scsi_host_type = {
  **/
 struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
 {
-	struct Scsi_Host *shost;
+	struct Scsi_Host *shost, *tmp_shost;
 	gfp_t gfp_mask = GFP_KERNEL;
 	int rval;
 
@@ -332,7 +332,18 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
 
 	mutex_init(&shost->scan_mutex);
 
+	/* 
+	 * Look if host_no is not been used somewhere else. Is is used to
+	 * happen when scsi_host_next_hn overflows and goes back to 0.
+	 */
+ host_no_already_exists:
 	shost->host_no = scsi_host_next_hn++; /* XXX(hch): still racy */
+        if(!IS_ERR(tmp_shost = scsi_host_lookup(shost->host_no)))
+          {
+            scsi_host_put(tmp_shost);
+            goto host_no_already_exists;
+          }
+
 	shost->dma_channel = 0xff;
 
 	/* These three are default values which can be overridden */

Re: scsi_host_alloc does not check for used shost->host_no

[Brian King]

Daniel Debonzi wrote:
> Hi everyone,
> 
> First of all, it is the first time I am sending something to one of the
> kernel mail lists. So, if it is not the right place for that, if it is
> not the only place for that, or I am doing something wrong, or wherever,
> please, just let me know.

A couple of comments regarding patch submission..

1. Read Documentation/SubmittingPatches and follow the guidelines contained
   within regarding patch format.
2. Subject should be something like:
	[PATCH] SCSI: scsi_host_alloc does not check for used shost->host_no

> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index c6457bf..2e191f4 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -310,7 +310,7 @@ struct device_type scsi_host_type = {
>   **/
>  struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
>  {
> -	struct Scsi_Host *shost;
> +	struct Scsi_Host *shost, *tmp_shost;
>  	gfp_t gfp_mask = GFP_KERNEL;
>  	int rval;
> 
> @@ -332,7 +332,18 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
> 
>  	mutex_init(&shost->scan_mutex);
> 
> +	/* 
> +	 * Look if host_no is not been used somewhere else. Is is used to
> +	 * happen when scsi_host_next_hn overflows and goes back to 0.
> +	 */
> + host_no_already_exists:
>  	shost->host_no = scsi_host_next_hn++; /* XXX(hch): still racy */
> +        if(!IS_ERR(tmp_shost = scsi_host_lookup(shost->host_no)))
> +          {

This needs to follow Documentation/CodingStyle, in this particular case, K&R braces.

> +            scsi_host_put(tmp_shost);
> +            goto host_no_already_exists;
> +          }
> +

Do we need to worry about a host in the SHOST_DEL state? In that case, it will still
exist to some degree, but scsi_host_get will fail. For example, what happens if a
shell is in /sys/class/scsi_host/host5/ and you delete host 5 and try to add another.
Couldn't you run into the same problem? In that case the scsi_host_get will fail.
I suppose you could check specifically for -ENXIO getting returned...

-Brian

-- 
Brian King
Linux on Power Virtualization
IBM Linux Technology Center

Re: scsi_host_alloc does not check for used shost->host_no

[Matthew Wilcox]

On Tue, Jul 15, 2008 at 03:16:28PM -0500, Brian King wrote:
> > +	/* 
> > +	 * Look if host_no is not been used somewhere else. Is is used to
> > +	 * happen when scsi_host_next_hn overflows and goes back to 0.
> > +	 */
> > + host_no_already_exists:
> >  	shost->host_no = scsi_host_next_hn++; /* XXX(hch): still racy */
> > +        if(!IS_ERR(tmp_shost = scsi_host_lookup(shost->host_no)))
> > +          {
> 
> This needs to follow Documentation/CodingStyle, in this particular case, K&R braces.

and assignments within conditionals are not preferred either:

	tmp_shost = scsi_host_lookup(shost->host_no);
	if (!IS_ERR(tmp_shost)) {
[...]

Oh, and gotos should be reserved for exception handling.  So this should
really be a loop:

	for (;;) {
		shost->host_no = scsi_host_next_hn++;
		tmp_shost = scsi_host_lookup(shost->host_no);
		if (IS_ERR(tmp_shost))
			continue;
		scsi_host_put(tmp_shost);
		break;
	}

> Do we need to worry about a host in the SHOST_DEL state? In that case, it will still
> exist to some degree, but scsi_host_get will fail. For example, what happens if a
> shell is in /sys/class/scsi_host/host5/ and you delete host 5 and try to add another.
> Couldn't you run into the same problem? In that case the scsi_host_get will fail.
> I suppose you could check specifically for -ENXIO getting returned...

Or we could make the host_no a u64 and avoid the problem ever happening
in our lifetimes.  I'm amazed that anyone's had the time to do 4 billion
add/removes, to be honest.  Assuming it takes 1 second per add/remove
cycle, and there's not even time to scan a bus in that time, that's
still 136 years.

-- 
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

Re: scsi_host_alloc does not check for used shost->host_no

[Brian King]

Matthew Wilcox wrote:
> Or we could make the host_no a u64 and avoid the problem ever happening
> in our lifetimes.  I'm amazed that anyone's had the time to do 4 billion
> add/removes, to be honest.  Assuming it takes 1 second per add/remove
> cycle, and there's not even time to scan a bus in that time, that's
> still 136 years.

That was my thought as well, until I checked struct scsi_host and saw
that hostno is actually defined as a short there, which makes the problem
slightly easier to hit. So, we could just increase both of them to u64's
and be done with it...

-Brian

-- 
Brian King
Linux on Power Virtualization
IBM Linux Technology Center

[PATCH] Make host_no an unsigned int

[Matthew Wilcox]

On Tue, Jul 15, 2008 at 03:31:47PM -0500, Brian King wrote:
> Matthew Wilcox wrote:
> > Or we could make the host_no a u64 and avoid the problem ever happening
> > in our lifetimes.  I'm amazed that anyone's had the time to do 4 billion
> > add/removes, to be honest.  Assuming it takes 1 second per add/remove
> > cycle, and there's not even time to scan a bus in that time, that's
> > still 136 years.
> 
> That was my thought as well, until I checked struct scsi_host and saw
> that hostno is actually defined as a short there, which makes the problem
> slightly easier to hit. So, we could just increase both of them to u64's
> and be done with it...

Oh, right.

It's an unsigned short, between two ints, so there's no additional space
consumed by making it an unsigned int.  An experienced hacker also notes
the 'SCSI_IOCTL_GET_IDLUN' comment, researches it, and finds out you
only get the bottom 8 bits of host_no anyway.

----

[PATCH] Make host_no an unsigned int

Daniel Debonzi reports that he has managed to wrap host_no.  Increasing
the number of host numbers available to 32-bit from 16-bit allows the
problem to be evaded for another hundred years.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 1834fdf..062161d 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -547,7 +547,7 @@ struct Scsi_Host {
 	unsigned int host_failed;	   /* commands that failed. */
 	unsigned int host_eh_scheduled;    /* EH scheduled without command */
     
-	unsigned short host_no;  /* Used for IOCTL_GET_IDLUN, /proc/scsi et al. */
+	unsigned int host_no;  /* Used for IOCTL_GET_IDLUN, /proc/scsi et al. */
 	int resetting; /* if set, it means that last_reset is a valid value */
 	unsigned long last_reset;
 

-- 
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

Re: scsi_host_alloc does not check for used shost->host_no

[James Bottomley]

On Tue, 2008-07-15 at 14:25 -0600, Matthew Wilcox wrote:
> > Do we need to worry about a host in the SHOST_DEL state? In that case, it will still
> > exist to some degree, but scsi_host_get will fail. For example, what happens if a
> > shell is in /sys/class/scsi_host/host5/ and you delete host 5 and try to add another.
> > Couldn't you run into the same problem? In that case the scsi_host_get will fail.
> > I suppose you could check specifically for -ENXIO getting returned...
> 
> Or we could make the host_no a u64 and avoid the problem ever happening
> in our lifetimes.  I'm amazed that anyone's had the time to do 4 billion
> add/removes, to be honest.  Assuming it takes 1 second per add/remove
> cycle, and there's not even time to scan a bus in that time, that's
> still 136 years.

Actually, right at the moment, a lot of the udev stuff is conditioned on
a non repeating host number (which is why we don't use idr like we do
for the other things).  I'm really reluctant to go to a u64 host
number ... what was the use case that produced this problem?

James

Re: scsi_host_alloc does not check for used shost->host_no

[Daniel Debonzi]

James Bottomley wrote:
> On Tue, 2008-07-15 at 14:25 -0600, Matthew Wilcox wrote:
>>> Do we need to worry about a host in the SHOST_DEL state? In that case, it will still
>>> exist to some degree, but scsi_host_get will fail. For example, what happens if a
>>> shell is in /sys/class/scsi_host/host5/ and you delete host 5 and try to add another.
>>> Couldn't you run into the same problem? In that case the scsi_host_get will fail.
>>> I suppose you could check specifically for -ENXIO getting returned...
>> Or we could make the host_no a u64 and avoid the problem ever happening
>> in our lifetimes.  I'm amazed that anyone's had the time to do 4 billion
>> add/removes, to be honest.  Assuming it takes 1 second per add/remove
>> cycle, and there's not even time to scan a bus in that time, that's
>> still 136 years.
> 
> Actually, right at the moment, a lot of the udev stuff is conditioned on
> a non repeating host number (which is why we don't use idr like we do
> for the other things).  I'm really reluctant to go to a u64 host
> number ... what was the use case that produced this problem?
> 
> James

All of it started in some functional tests against pata_pdc2027x module 
which includes some rmmod/modprobe (around 10000). Before I start to 
work on it, this functional test started to fail, sometimes with at 
different points.

Just to make clear, I am adding some kernel messages and mon info to 
help some additional comments.

We can see that on the first and Third times (on rmmod) a panic happened 
far to the short int border (around 19741 and 9887). On the Second we 
can see that it happens on modprobe when going from 65355 to 0. This 
pointed me to the patch I summited and which I used to check if all of 
it would be "fixed". After that patch (I know it is far away from a good 
patch) I got this rmmod/modprobe loop running for more then 4 days with 
no kernel panic. It made me believe that somehow it avoids the First and 
Third panics to happen.

I am pretty knew to this peaces of code and I probably don't have a full 
overview of it. That is way I would like to have your input and opinions.

I really appreciate that.
Daniel Debonzi

First occurrence:
**********************************************
    Vendor: IBM       Model: DROM00205         Rev: NR36
   Type:   CD-ROM                             ANSI SCSI revision: 02
sr0: scsi3-mmc drive: 61x/61x cd/rw xa/form2 cdda tray
sr 19740:0:0:0: Attached scsi generic sg4 type 5
ata19739.00: disabled
   Vendor: IBM       Model: DROM00205         Rev: NR36
   Type:   CD-ROM                             ANSI SCSI revision: 02
sr0: scsi3-mmc drive: 61x/61x cd/rw xa/form2 cdda tray
sr 19742:0:0:0: Attached scsi generic sg4 type 5
ata19741.00: disabled
Unable to handle kernel paging request for data at address 
0xd0000000008c3e98
Faulting instruction address: 0xd0000000001db250
cpu 0x3: Vector: 300 (Data Access) at [c0000000391173c0]
     pc: d0000000001db250: .scsi_target_reap_usercontext+0x90/0x114 
[scsi_mod]
     lr: d0000000001db244: .scsi_target_reap_usercontext+0x84/0x114 
[scsi_mod]
     sp: c000000039117640
    msr: 8000000000001032
    dar: d0000000008c3e98
  dsisr: 40000000
   current = 0xc00000007182dc60
   paca    = 0xc000000000475400
     pid   = 535, comm = udevd


3:mon> t
[c0000000391176e0] c00000000007f35c .execute_in_process_context+0x54/0xa0
[c000000039117760] d0000000001da190 .scsi_target_reap+0xc8/0x100 [scsi_mod]
[c0000000391177f0] d0000000001db5c8 
.scsi_device_dev_release_usercontext+0xc8/0x
120 [scsi_mod]
[c0000000391178a0] c00000000007f35c .execute_in_process_context+0x54/0xa0
[c000000039117920] d0000000001db4e8 .scsi_device_dev_release+0x24/0x3c 
[scsi_mod
]
[c0000000391179a0] c00000000022580c .device_release+0x4c/0x78
[c000000039117a20] c0000000001b2388 .kobject_cleanup+0x90/0xf0
[c000000039117ac0] c0000000001b3470 .kref_put+0x84/0xa0
[c000000039117b40] c0000000001b22e0 .kobject_put+0x28/0x40
[c000000039117bc0] c00000000014dbe8 .sysfs_release+0x48/0xe0
[c000000039117c50] c0000000000eca1c .__fput+0x108/0x25c
[c000000039117d00] c0000000000e8fa4 .filp_close+0xac/0xd4
[c000000039117d90] c0000000000eacf4 .sys_close+0xc4/0x110
[c000000039117e30] c0000000000086a4 syscall_exit+0x0/0x40
--- Exception: c00 (System Call) at 0000000007e7d7d0
SP (ff8dc360) is in userspace

**********************************************

Second occurrence:
**********************************************
*  Vendor: IBM       Model: DROM00205         Rev: NR38
   Type:   CD-ROM                             ANSI SCSI revision: 02
sr0: scsi3-mmc drive: 24x/24x cd/rw xa/form2 cdda tray
sr 65529:0:0:0: Attached scsi generic sg11 type 5
ata65529.00: disabled
   Vendor: IBM       Model: DROM00205         Rev: NR38
   Type:   CD-ROM                             ANSI SCSI revision: 02
sr0: scsi3-mmc drive: 24x/24x cd/rw xa/form2 cdda tray
sr 65531:0:0:0: Attached scsi generic sg11 type 5
ata65531.00: disabled
   Vendor: IBM       Model: DROM00205         Rev: NR38
   Type:   CD-ROM                             ANSI SCSI revision: 02
sr0: scsi3-mmc drive: 24x/24x cd/rw xa/form2 cdda tray
sr 65533:0:0:0: Attached scsi generic sg11 type 5
ata65533.00: disabled
kobject_add failed for host0 with -EEXIST, don't try to register things 
with the
same name in the same directory.
Call Trace:
[C0000000B565B1A0] [C00000000000FFDC] .show_stack+0x68/0x1b0 (unreliable)
[C0000000B565B240] [C0000000001B28E0] .kobject_add+0x1a4/0x1fc
[C0000000B565B2E0] [C000000000229EE0] .class_device_add+0xb4/0x4e4
[C0000000B565B3B0] [D0000000001D1F2C] .scsi_add_host+0xf8/0x208 [scsi_mod]
[C0000000B565B450] [D00000000052B52C] .ata_scsi_add_hosts+0xa4/0x160 
[libata]
[C0000000B565B500] [D000000000527C0C] .ata_host_register+0xec/0x368 [libata]
[C0000000B565B5D0] [D000000000527F1C] .ata_host_activate+0x94/0xe0 [libata]
[C0000000B565B680] [D0000000007D11B0] .pdc2027x_init_one+0x36c/0x39c 
[pata_pdc2027x]
[C0000000B565B730] [C0000000001C3530] .pci_device_probe+0x13c/0x1dc
[C0000000B565B7F0] [C0000000002287F0] .driver_probe_device+0xa0/0x16c
[C0000000B565B890] [C000000000228A58] .__driver_attach+0xb4/0x138
[C0000000B565B920] [C000000000227F14] .bus_for_each_dev+0x7c/0xd4
[C0000000B565B9E0] [C000000000228694] .driver_attach+0x28/0x40
[C0000000B565BA60] [C00000000022797C] .bus_add_driver+0x98/0x18c
[C0000000B565BB00] [C000000000228E58] .driver_register+0xa8/0xc4
[C0000000B565BB80] [C0000000001C3838] .__pci_register_driver+0x5c/0xa4
[C0000000B565BC10] [D0000000007D14D4] .pdc2027x_init+0x20/0x45c 
[pata_pdc2027x]
[C0000000B565BC90] [C000000000090B50] .sys_init_module+0x1764/0x1998
[C0000000B565BE30] [C0000000000086A4] syscall_exit+0x0/0x40
slab error in kmem_cache_destroy(): cache `scsi_cmd_cache': Can't free 
all objects
Call Trace:
[C0000000B565B070] [C00000000000FFDC] .show_stack+0x68/0x1b0 (unreliable)
[C0000000B565B110] [C0000000000E4020] .kmem_cache_destroy+0x94/0x1b0
[C0000000B565B1A0] [D0000000001D12D8] 
.scsi_destroy_command_freelist+0xa0/0xcc
[scsi_mod]
[C0000000B565B230] [D0000000001D1720] .scsi_host_dev_release+0x80/0xe0 
[scsi_mod]
[C0000000B565B2C0] [C00000000022580C] .device_release+0x4c/0x78
[C0000000B565B340] [C0000000001B2388] .kobject_cleanup+0x90/0xf0
[C0000000B565B3E0] [C0000000001B3470] .kref_put+0x84/0xa0
[C0000000B565B460] [C0000000001B22E0] .kobject_put+0x28/0x40
[C0000000B565B4E0] [C000000000225968] .put_device+0x1c/0x30
[C0000000B565B560] [D0000000001D168C] .scsi_host_put+0x14/0x28 [scsi_mod]
[C0000000B565B5E0] [D000000000528058] .ata_host_release+0xf0/0x14c [libata]
[C0000000B565B680] [C00000000022C720] .release_nodes+0x1c8/0x22c
[C0000000B565B750] [C00000000022CB98] .devres_release_all+0x58/0xd4
[C0000000B565B7F0] [C000000000228860] .driver_probe_device+0x110/0x16c
[C0000000B565B890] [C000000000228A58] .__driver_attach+0xb4/0x138
[C0000000B565B920] [C000000000227F14] .bus_for_each_dev+0x7c/0xd4
[C0000000B565B9E0] [C000000000228694] .driver_attach+0x28/0x40
[C0000000B565BA60] [C00000000022797C] .bus_add_driver+0x98/0x18c
[C0000000B565BB00] [C000000000228E58] .driver_register+0xa8/0xc4
[C0000000B565BB80] [C0000000001C3838] .__pci_register_driver+0x5c/0xa4
[C0000000B565BC10] [D0000000007D14D4] .pdc2027x_init+0x20/0x45c 
[pata_pdc2027x]
[C0000000B565BC90] [C000000000090B50] .sys_init_module+0x1764/0x1998
[C0000000B565BE30] [C0000000000086A4] syscall_exit+0x0/0x40
Unable to handle kernel paging request for data at address 
0x3a30322e332f3040
Faulting instruction address: 0xc0000000000843e4
cpu 0x4: Vector: 300 (Data Access) at [c0000000b565af10]
     pc: c0000000000843e4: .kthread_stop+0x3c/0xfc
     lr: c0000000000843e0: .kthread_stop+0x38/0xfc
     sp: c0000000b565b190
    msr: 8000000000009032
    dar: 3a30322e332f3040
  dsisr: 40000000
   current = 0xc0000000ea1294d0
   paca    = 0xc000000000475600
     pid   = 15221, comm = modprobe
*********************************************



Third occurrence:
**********************************************
  <7>pata_pdc2027x 0001:cc:01.0: version 0.74-ac5
<6>pata_pdc2027x 0001:cc:01.0: PLL input clock 32758 kHz
<6>ata9887: PATA max UDMA/133 cmd 0xD000080084DC07C0 ctl 0xD000080084DC0FDA
bmdma 0xD000080084DC0000 irq 166
<6>ata9888: PATA max UDMA/133 cmd 0xD000080084DC05C0 ctl 0xD000080084DC0DDA
bmdma 0xD000080084DC0008 irq 166
<6>scsi9887 : pata_pdc2027x
<6>ata9887.00: ATAPI, max UDMA/33
<6>ata9887.00: configured for UDMA/33
<6>scsi9888 : pata_pdc2027x
<4>ATA: abnormal status 0x8 on port 0xD000080084DC05DF
<5>  Vendor: IBM       Model: DROM00205         Rev: NR36
<5>  Type:   CD-ROM                             ANSI SCSI revision: 02
<4>sr0: scsi3-mmc drive: 61x/61x cd/rw xa/form2 cdda tray
<7>sr 9887:0:0:0: Attached scsi CD-ROM sr0
<5>sr 9887:0:0:0: Attached scsi generic sg0 type 5
<4>ata9887.00: disabled
<1>Unable to handle kernel paging request for data at address 
0xd000000000047878
<1>Faulting instruction address: 0xd0000000000821f0
cpu 0x1: Vector: 300 (Data Access) at [c000000070f03580]
     pc: d0000000000821f0: 
.scsi_device_dev_release_usercontext+0x40/0x1ac [scsi_mod]
     lr: c000000000077394: .execute_in_process_context+0x54/0xa0
     sp: c000000070f03800
    msr: 8000000000009032
    dar: d000000000047878
  dsisr: 40000000
   current = 0xc000000002cacad0
   paca    = 0xc0000000004a3780
     pid   = 2086, comm = hald