Re: PATCH: 2.4.22-pre7 drivers/i2c/i2c-dev.c user/kernel bug and mem leak

Re: PATCH: 2.4.22-pre7 drivers/i2c/i2c-dev.c user/kernel bug and mem leak

[Jean Delvare]

Hi all,

Ten days ago, Robert T. Johnson repported two bugs in 2.4's
drivers/i2c/i2c-dev.c. It also applies to i2c CVS (out of kernel), which
is intended to become 2.4's soon. Being a member of the LM Sensors dev
team, I took a look at the repport. My knowledge is somewhat limited but
I'll do my best to help (unless Greg wants to handle it alone? ;-)).

For the user/kernel bug, I'm not sure I understand how copy_from_user is
supposed to work. If I understand what the proposed patch does, it
simply allocates a second buffer, copy_from_user to that buffer instead
of to the original one, and then copies from that second buffer to the
original one (kernel to kernel). I just don't see how different it is
from what the current code does, as far as user/kernel issues are
concerned. I must be missing something obvious, can someone please bring
me some light?

For the mem leak bug, it's clearly there. I admit the proposed patch
fixes it, but I think there is a better way to fix it. Compare what the
proposed patch does:

--- i2c-dev.c	Sun Aug  3 18:24:33 2003
+++ i2c-dev.c.proposed	Sun Aug  3 19:13:58 2003
@@ -226,6 +226,7 @@
 		res = 0;
 		for( i=0; i<rdwr_arg.nmsgs; i++ )
 		{
+			rdwr_pa[i].buf = NULL;
 		    	if(copy_from_user(&(rdwr_pa[i]),
 					&(rdwr_arg.msgs[i]),
 					sizeof(rdwr_pa[i])))
@@ -254,8 +255,9 @@
 		}
 		if (res < 0) {
 			int j;
-			for (j = 0; j < i; ++j)
-				kfree(rdwr_pa[j].buf);
+			for (j = 0; j <= i; ++j)
+				if (rdwr_pa[j].buf)
+					kfree(rdwr_pa[j].buf);
 			kfree(rdwr_pa);
 			return res;
 		}

with what I suggest:

--- i2c-dev.c	Sun Aug  3 18:24:33 2003
+++ i2c-dev.c.khali	Sun Aug  3 19:15:04 2003
@@ -247,8 +247,9 @@
 			if(copy_from_user(rdwr_pa[i].buf,
 				rdwr_arg.msgs[i].buf,
 				rdwr_pa[i].len))
 			{
+				kfree(rdwr_pa[i].buf);
 			    	res = -EFAULT;
 				break;
 			}
 		}

Contrary to the proposed fix, my fix does not slow down the non-faulty
cases. I also believe it will increase the code size by fewer bytes than
the proposed fix (not verified though).

So, what about it?



PS: I really would like to see Frodo Looijaard's address replaced with
the LM Sensors mailing list address <sensors@stimpy.netroedge.com> as
the main I2C contact in MAINTAINERS. Simon Vogl and Frodo Looijaard's
have been doing a really great job, but they do not work actively on I2C
anymore, so they end up forwarding every repport to the list anyway.

-- 
Jean Delvare
http://www.ensicaen.ismra.fr/~delvare/

Re: PATCH: 2.4.22-pre7 drivers/i2c/i2c-dev.c user/kernel bug and mem leak

[Sergey Vlasov]

On Sun, 3 Aug 2003 19:23:12 +0200
Jean Delvare <khali@linux-fr.org> wrote:

> Ten days ago, Robert T. Johnson repported two bugs in 2.4's
> drivers/i2c/i2c-dev.c. It also applies to i2c CVS (out of kernel), which
> is intended to become 2.4's soon. Being a member of the LM Sensors dev
> team, I took a look at the repport. My knowledge is somewhat limited but
> I'll do my best to help (unless Greg wants to handle it alone? ;-)).
> 
> For the user/kernel bug, I'm not sure I understand how copy_from_user is
> supposed to work. If I understand what the proposed patch does, it
> simply allocates a second buffer, copy_from_user to that buffer instead
> of to the original one, and then copies from that second buffer to the
> original one (kernel to kernel). I just don't see how different it is
> from what the current code does, as far as user/kernel issues are
> concerned. I must be missing something obvious, can someone please bring
> me some light?

The current code takes rdwr_arg.msgs (which is a userspace pointer)
and then reads rdwr_arg.msgs[i].buf directly, which must not be done.
This is done in two places - when copying the user data before
i2c_transfer(), and when copying the result back to the userspace
after it.

Because both the userspace pointer and the kernel buffer pointer are
needed, a second copy must be made. If you want to conserve memory,
you may just allocate an array of pointers to keep the userspace
buffer pointers during the transfer.

BTW, an optimization is possible here: the whole rdwr_arg.msgs array
can be copied into the kernel memory with one copy_from_user() instead
of copying its items one by one.

> For the mem leak bug, it's clearly there. I admit the proposed patch
> fixes it, but I think there is a better way to fix it. Compare what the
> proposed patch does:
> 
> --- i2c-dev.c	Sun Aug  3 18:24:33 2003
> +++ i2c-dev.c.proposed	Sun Aug  3 19:13:58 2003
> @@ -226,6 +226,7 @@
>  		res = 0;
>  		for( i=0; i<rdwr_arg.nmsgs; i++ )
>  		{
> +			rdwr_pa[i].buf = NULL;
>  		    	if(copy_from_user(&(rdwr_pa[i]),
>  					&(rdwr_arg.msgs[i]),
>  					sizeof(rdwr_pa[i])))
> @@ -254,8 +255,9 @@
>  		}
>  		if (res < 0) {
>  			int j;
> -			for (j = 0; j < i; ++j)
> -				kfree(rdwr_pa[j].buf);
> +			for (j = 0; j <= i; ++j)
> +				if (rdwr_pa[j].buf)
> +					kfree(rdwr_pa[j].buf);
>  			kfree(rdwr_pa);
>  			return res;
>  		}
> 
> with what I suggest:
> 
> --- i2c-dev.c	Sun Aug  3 18:24:33 2003
> +++ i2c-dev.c.khali	Sun Aug  3 19:15:04 2003
> @@ -247,8 +247,9 @@
>  			if(copy_from_user(rdwr_pa[i].buf,
>  				rdwr_arg.msgs[i].buf,
>  				rdwr_pa[i].len))
>  			{
> +				kfree(rdwr_pa[i].buf);
>  			    	res = -EFAULT;
>  				break;
>  			}
>  		}
> 
> Contrary to the proposed fix, my fix does not slow down the non-faulty
> cases. I also believe it will increase the code size by fewer bytes than
> the proposed fix (not verified though).

This fix should work too. Yet another way is to do ++i there, but that
would be too obscure.

> So, what about it?

Here is my version (with the mentioned optimization - warning: not
even compiled):

--- i2c-dev.c.old	2003-07-28 16:14:34 +0400
+++ i2c-dev.c	2003-08-04 19:28:25 +0400
@@ -171,6 +171,7 @@
 	struct i2c_smbus_ioctl_data data_arg;
 	union i2c_smbus_data temp;
 	struct i2c_msg *rdwr_pa;
+	u8 **data_ptrs;
 	int i,datasize,res;
 	unsigned long funcs;
 
@@ -223,21 +224,28 @@
 
 		if (rdwr_pa == NULL) return -ENOMEM;
 
+		if (copy_from_user(rdwr_pa, rdwr_arg.msgs,
+				   rdwr_arg.nmsgs * sizeof(struct i2c_msg))) {
+			kfree(rdwr_pa);
+			return -EFAULT;
+		}
+
+		data_ptrs = (u8 **) kmalloc(rdwr_arg.nmsgs * sizeof(u8 *),
+					    GFP_KERNEL);
+		if (data_ptrs == NULL) {
+			kfree(rdwr_pa);
+			return -ENOMEM;
+		}
+
 		res = 0;
 		for( i=0; i<rdwr_arg.nmsgs; i++ )
 		{
-		    	if(copy_from_user(&(rdwr_pa[i]),
-					&(rdwr_arg.msgs[i]),
-					sizeof(rdwr_pa[i])))
-			{
-			        res = -EFAULT;
-				break;
-			}
 			/* Limit the size of the message to a sane amount */
 			if (rdwr_pa[i].len > 8192) {
 				res = -EINVAL;
 				break;
 			}
+			data_ptrs[i] = rdwr_pa[i].buf;
 			rdwr_pa[i].buf = kmalloc(rdwr_pa[i].len, GFP_KERNEL);
 			if(rdwr_pa[i].buf == NULL)
 			{
@@ -245,9 +253,10 @@
 				break;
 			}
 			if(copy_from_user(rdwr_pa[i].buf,
-				rdwr_arg.msgs[i].buf,
+				data_ptrs[i],
 				rdwr_pa[i].len))
 			{
+				kfree(rdwr_pa[i].buf);
 			    	res = -EFAULT;
 				break;
 			}
@@ -256,6 +265,7 @@
 			int j;
 			for (j = 0; j < i; ++j)
 				kfree(rdwr_pa[j].buf);
+			kfree(data_ptrs);
 			kfree(rdwr_pa);
 			return res;
 		}
@@ -270,7 +280,7 @@
 			if( res>=0 && (rdwr_pa[i].flags & I2C_M_RD))
 			{
 				if(copy_to_user(
-					rdwr_arg.msgs[i].buf,
+					data_ptrs[i],
 					rdwr_pa[i].buf,
 					rdwr_pa[i].len))
 				{
@@ -279,6 +289,7 @@
 			}
 			kfree(rdwr_pa[i].buf);
 		}
+		kfree(data_ptrs);
 		kfree(rdwr_pa);
 		return res;
 

Re: PATCH: 2.4.22-pre7 drivers/i2c/i2c-dev.c user/kernel bug and mem leak

[Jean Delvare]

> The current code takes rdwr_arg.msgs (which is a userspace pointer)
> and then reads rdwr_arg.msgs[i].buf directly, which must not be done.

The reason why this must not be done is unknown to me. This is why I am
having a hard time figuring why a fix is necessary. If someone can
explain this to me (off list I guess, unless it is of general interest),
he/she would be welcome.

Anyway, since you seem to agree with Robert T. Johnson on the fact that
this needs to be fixed, I have to believe you. But then again I am not
sure I understand how different your code is from the original one if
copy_to_user and copy_from_user are regular functions. Are these macros?
Maybe taking a look at them would help me understand how the whole thing
works.

> Because both the userspace pointer and the kernel buffer pointer are
> needed, a second copy must be made.

OK, I get this now (wasn't that obvious at first, especially because I
hadn't realized the values were used again after i2c_transfer).

> If you want to conserve memory, you may just allocate an array
> of pointers to keep the userspace buffer pointers during the
> transfer.

Definitely better than what Robert T. Johnson first proposed. This makes
it really clear what data actually needs to be "duplicated" and what
doesn't.

> BTW, an optimization is possible here: the whole rdwr_arg.msgs array
> can be copied into the kernel memory with one copy_from_user() instead
> of copying its items one by one.

Nice one, I like it.

> > Contrary to the proposed fix, my fix does not slow down the
> > non-faulty cases. I also believe it will increase the code size by
> > fewer bytes than the proposed fix (not verified though).
> 
> This fix should work too. Yet another way is to do ++i there, but that
> would be too obscure.

I don't find it that obscure, and after thinking about it for some
times, I even find it more elegant. And I guess it's smaller
(binary-code-wise), although I admit it's almost pointless.

> Here is my version (with the mentioned optimization - warning: not
> even compiled):

Really, I like it much more than Robert's one. It's probably faster,
uses less memory, and was easier to read and understand.

Here comes my version, which is basically yours modified. If it pleases
everyone, we could apply it to 2.4.22-pre10 and i2c-CVS.

Changes:
1* Amount of white space, twice. Ignore.
2* Use ++i instead of kfree as discussed above.
3* Remove conditional test around i2c_transfer, since it isn't necessary
(if I'm not missing something).

diff -ru drivers/i2c/i2c-dev.c drivers/i2c/i2c-dev.c
--- drivers/i2c/i2c-dev.c	Tue Jul 15 12:23:49 2003
+++ drivers/i2c/i2c-dev.c	Tue Aug  5 09:56:50 2003
@@ -219,6 +219,7 @@
 	struct i2c_smbus_ioctl_data data_arg;
 	union i2c_smbus_data temp;
 	struct i2c_msg *rdwr_pa;
+	u8 **data_ptrs;
 	int i,datasize,res;
 	unsigned long funcs;
 
@@ -248,7 +249,7 @@
 		return (copy_to_user((unsigned long *)arg,&funcs,
 		                     sizeof(unsigned long)))?-EFAULT:0;
 
-        case I2C_RDWR:
+	case I2C_RDWR:
 		if (copy_from_user(&rdwr_arg, 
 				   (struct i2c_rdwr_ioctl_data *)arg, 
 				   sizeof(rdwr_arg)))
@@ -265,21 +266,28 @@
 
 		if (rdwr_pa == NULL) return -ENOMEM;
 
+		if (copy_from_user(rdwr_pa, rdwr_arg.msgs,
+				   rdwr_arg.nmsgs * sizeof(struct i2c_msg))) {
+			kfree(rdwr_pa);
+			return -EFAULT;
+		}
+
+		data_ptrs = (u8 **) kmalloc(rdwr_arg.nmsgs * sizeof(u8 *),
+					    GFP_KERNEL);
+		if (data_ptrs == NULL) {
+			kfree(rdwr_pa);
+			return -ENOMEM;
+		}
+
 		res = 0;
 		for( i=0; i<rdwr_arg.nmsgs; i++ )
 		{
-		    	if(copy_from_user(&(rdwr_pa[i]),
-					&(rdwr_arg.msgs[i]),
-					sizeof(rdwr_pa[i])))
-			{
-			        res = -EFAULT;
-				break;
-			}
 			/* Limit the size of the message to a sane amount */
 			if (rdwr_pa[i].len > 8192) {
 				res = -EINVAL;
 				break;
 			}
+			data_ptrs[i] = rdwr_pa[i].buf;
 			rdwr_pa[i].buf = kmalloc(rdwr_pa[i].len, GFP_KERNEL);
 			if(rdwr_pa[i].buf == NULL)
 			{
@@ -287,10 +295,11 @@
 				break;
 			}
 			if(copy_from_user(rdwr_pa[i].buf,
-				rdwr_arg.msgs[i].buf,
+				data_ptrs[i],
 				rdwr_pa[i].len))
 			{
-			    	res = -EFAULT;
+				++i; /* Needs to be kfreed too */
+				res = -EFAULT;
 				break;
 			}
 		}
@@ -298,21 +307,19 @@
 			int j;
 			for (j = 0; j < i; ++j)
 				kfree(rdwr_pa[j].buf);
+			kfree(data_ptrs);
 			kfree(rdwr_pa);
 			return res;
 		}
-		if (!res) 
-		{
-			res = i2c_transfer(client->adapter,
-				rdwr_pa,
-				rdwr_arg.nmsgs);
-		}
+		res = i2c_transfer(client->adapter,
+			rdwr_pa,
+			rdwr_arg.nmsgs);
 		while(i-- > 0)
 		{
 			if( res>=0 && (rdwr_pa[i].flags & I2C_M_RD))
 			{
 				if(copy_to_user(
-					rdwr_arg.msgs[i].buf,
+					data_ptrs[i],
 					rdwr_pa[i].buf,
 					rdwr_pa[i].len))
 				{
@@ -321,6 +328,7 @@
 			}
 			kfree(rdwr_pa[i].buf);
 		}
+		kfree(data_ptrs);
 		kfree(rdwr_pa);
 		return res;
 


-- 
Jean Delvare
http://www.ensicaen.ismra.fr/~delvare/

Re: PATCH: 2.4.22-pre7 drivers/i2c/i2c-dev.c user/kernel bug and mem leak

[Sergey Vlasov]

On Tue, 5 Aug 2003 10:32:40 +0200
Jean Delvare <khali@linux-fr.org> wrote:

> > The current code takes rdwr_arg.msgs (which is a userspace pointer)
> > and then reads rdwr_arg.msgs[i].buf directly, which must not be done.
> 
> The reason why this must not be done is unknown to me. This is why I am
> having a hard time figuring why a fix is necessary. If someone can
> explain this to me (off list I guess, unless it is of general interest),
> he/she would be welcome.

All userspace access from the kernel code must be guarded - otherwise
an invalid address supplied by a buggy or malicious program can crash
the kernel or make it perform something which is not normally allowed.
Unchecked userspace access is a security problem.

In this particular case the address has already been checked by
copy_from_user() before - but the access still is not safe. Example:

1) A multithreaded program calls the I2C_RDWR ioctl in one thread,
passing some valid address in rdwr_arg.msgs. The code in i2c-dev gets
the supplied parameters and calls i2c_transfer(), which sleeps.

2) While the first thread is sleeping somewhere inside i2c_transfer(),
the second thread unmaps the page where the rdwr_arg.msgs array was
located.

3) When i2c_transfer() completes, the I2C_RDWR handling code will try
to copy the returned data to the user memory, and will try to access
rdwr_arg.msgs[i].buf in the loop. But now this page is inaccessible,
and the access will result in Oops.

Also see the recent LKML postings (Kernel Traffic #224, "Better
Support For Big-RAM Systems"); with the 4G/4G configuration described
there, direct userspace access will not work at all.

> Anyway, since you seem to agree with Robert T. Johnson on the fact that
> this needs to be fixed, I have to believe you. But then again I am not
> sure I understand how different your code is from the original one if
> copy_to_user and copy_from_user are regular functions. Are these macros?

Yes, hairy macros with assembler tricks.

> Maybe taking a look at them would help me understand how the whole thing
> works.

You should not depend on implementation details. All userspace access
must be performed through the documented macros. Doing something other
is a bug - possibly a very dangerous one.

> > Because both the userspace pointer and the kernel buffer pointer are
> > needed, a second copy must be made.
> 
> OK, I get this now (wasn't that obvious at first, especially because I
> hadn't realized the values were used again after i2c_transfer).
> 
> > If you want to conserve memory, you may just allocate an array
> > of pointers to keep the userspace buffer pointers during the
> > transfer.
> 
> Definitely better than what Robert T. Johnson first proposed. This makes
> it really clear what data actually needs to be "duplicated" and what
> doesn't.
> 
> > BTW, an optimization is possible here: the whole rdwr_arg.msgs array
> > can be copied into the kernel memory with one copy_from_user() instead
> > of copying its items one by one.
> 
> Nice one, I like it.
> 
> > > Contrary to the proposed fix, my fix does not slow down the
> > > non-faulty cases. I also believe it will increase the code size by
> > > fewer bytes than the proposed fix (not verified though).
> > 
> > This fix should work too. Yet another way is to do ++i there, but that
> > would be too obscure.
> 
> I don't find it that obscure, and after thinking about it for some
> times, I even find it more elegant. And I guess it's smaller
> (binary-code-wise), although I admit it's almost pointless.
> 
> > Here is my version (with the mentioned optimization - warning: not
> > even compiled):
> 
> Really, I like it much more than Robert's one. It's probably faster,
> uses less memory, and was easier to read and understand.
> 
> Here comes my version, which is basically yours modified. If it pleases
> everyone, we could apply it to 2.4.22-pre10 and i2c-CVS.
> 
> Changes:
> 1* Amount of white space, twice. Ignore.
> 2* Use ++i instead of kfree as discussed above.
> 3* Remove conditional test around i2c_transfer, since it isn't necessary
> (if I'm not missing something).

Yes, looks like the test is redundant.

> diff -ru drivers/i2c/i2c-dev.c drivers/i2c/i2c-dev.c
[patch skipped]

Looks good to me.

Re: PATCH: 2.4.22-pre7 drivers/i2c/i2c-dev.c user/kernel bug and mem leak

[Greg KH]

On Tue, Aug 05, 2003 at 10:32:40AM +0200, Jean Delvare wrote:
> 
> Changes:
> 1* Amount of white space, twice. Ignore.
> 2* Use ++i instead of kfree as discussed above.
> 3* Remove conditional test around i2c_transfer, since it isn't necessary
> (if I'm not missing something).

Patch looks good, want to send it to Marcelo, or do you want me to?

thanks,

greg k-h

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Jean Delvare]

Hi Marcelo,

Greg> Patch looks good, want to send it to Marcelo, or do you want me
Greg> to?

Here I do, speaking in the name of the I2C & LM Sensors development team
:)

A patch to i2c-dev follows, built against 2.4.22-pre10, which brings
the following changes:

* Fix a user/kernel bug discovered by Robert T. Johnson.
  Patch by Sergey Vlasov.
* Fix a memory leak discovered by Robert T. Johnson.
  Patch by Sergey Vlasov and me.
* Two code optimizations/cleanups.
  Patches by Sergey Vlaslov and me, respectively.
* Bonus: two lines with changed whitespace, but you don't care.
  Patches by me and Robert T. Johnson, respectively.

These changes should also be made to i2c-CVS and Linux 2.6's i2c
subsystem. I will commit the changes to i2c-CVS while Greg KH will
submit a modified patch to Linus.

The final patch was tested by me (compiles and runs with no apparent
drawback) and approved by Sergey Vlaslov and Greg KH.
Please apply.

Thanks,
Jean


--- 2.4/drivers/i2c/i2c-dev.c	Tue Jul 15 12:23:49 2003
+++ 2.4/drivers/i2c/i2c-dev.c	Wed Aug  6 09:36:54 2003
@@ -219,6 +219,7 @@
 	struct i2c_smbus_ioctl_data data_arg;
 	union i2c_smbus_data temp;
 	struct i2c_msg *rdwr_pa;
+	u8 **data_ptrs;
 	int i,datasize,res;
 	unsigned long funcs;
 
@@ -248,7 +249,7 @@
 		return (copy_to_user((unsigned long *)arg,&funcs,
 		                     sizeof(unsigned long)))?-EFAULT:0;
 
-        case I2C_RDWR:
+	case I2C_RDWR:
 		if (copy_from_user(&rdwr_arg, 
 				   (struct i2c_rdwr_ioctl_data *)arg, 
 				   sizeof(rdwr_arg)))
@@ -265,21 +266,28 @@
 
 		if (rdwr_pa == NULL) return -ENOMEM;
 
+		if (copy_from_user(rdwr_pa, rdwr_arg.msgs,
+				   rdwr_arg.nmsgs * sizeof(struct i2c_msg))) {
+			kfree(rdwr_pa);
+			return -EFAULT;
+		}
+
+		data_ptrs = (u8 **) kmalloc(rdwr_arg.nmsgs * sizeof(u8 *),
+					    GFP_KERNEL);
+		if (data_ptrs == NULL) {
+			kfree(rdwr_pa);
+			return -ENOMEM;
+		}
+
 		res = 0;
 		for( i=0; i<rdwr_arg.nmsgs; i++ )
 		{
-		    	if(copy_from_user(&(rdwr_pa[i]),
-					&(rdwr_arg.msgs[i]),
-					sizeof(rdwr_pa[i])))
-			{
-			        res = -EFAULT;
-				break;
-			}
 			/* Limit the size of the message to a sane amount */
 			if (rdwr_pa[i].len > 8192) {
 				res = -EINVAL;
 				break;
 			}
+			data_ptrs[i] = rdwr_pa[i].buf;
 			rdwr_pa[i].buf = kmalloc(rdwr_pa[i].len, GFP_KERNEL);
 			if(rdwr_pa[i].buf == NULL)
 			{
@@ -287,10 +295,11 @@
 				break;
 			}
 			if(copy_from_user(rdwr_pa[i].buf,
-				rdwr_arg.msgs[i].buf,
+				data_ptrs[i],
 				rdwr_pa[i].len))
 			{
-			    	res = -EFAULT;
+				++i; /* Needs to be kfreed too */
+				res = -EFAULT;
 				break;
 			}
 		}
@@ -298,21 +307,20 @@
 			int j;
 			for (j = 0; j < i; ++j)
 				kfree(rdwr_pa[j].buf);
+			kfree(data_ptrs);
 			kfree(rdwr_pa);
 			return res;
 		}
-		if (!res) 
-		{
-			res = i2c_transfer(client->adapter,
-				rdwr_pa,
-				rdwr_arg.nmsgs);
-		}
+
+		res = i2c_transfer(client->adapter,
+			rdwr_pa,
+			rdwr_arg.nmsgs);
 		while(i-- > 0)
 		{
 			if( res>=0 && (rdwr_pa[i].flags & I2C_M_RD))
 			{
 				if(copy_to_user(
-					rdwr_arg.msgs[i].buf,
+					data_ptrs[i],
 					rdwr_pa[i].buf,
 					rdwr_pa[i].len))
 				{
@@ -321,6 +329,7 @@
 			}
 			kfree(rdwr_pa[i].buf);
 		}
+		kfree(data_ptrs);
 		kfree(rdwr_pa);
 		return res;
 


-- 
Jean Delvare
http://www.ensicaen.ismra.fr/~delvare/

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Robert T. Johnson]

On Thu, 2003-08-14 at 12:09, Greg KH wrote:
> Hm, much like Linus's sparse does already?  :)

Yes, but cqual needs fewer annotations (see below).

> His checker missed the 2.6 version of this, for some reason, I haven't
> taken the time to figure out why.

Currently, sparse silently ignores missing annotations.  Since i2c-dev.c
is not extensively annotated, it missed this bug.  Cqual requires _very_
few annotations (we use about 200 for the whole kernel -- almost all of
them on sys_* functions).  Cqual can use additional annotations, but
they're not required.

Also, cqual is more flexible than sparse.  For example, i2c-dev.c wants
to use some i2c_msg structures to hold user bufs, and some to hold
kernel bufs.  cqual handles this automatically, but sparse cannot at
all.  To get i2c-dev.c to work with sparse, you'd need to declare two
new types, "struct kernel_i2c_msg" and "struct user_i2c_msg", and change
every instance of i2c_msg to be one or the other.  You'd also end up
manually copying fields between them in the ioctl.  So I think the patch
I'm submitting with this email is not only required to pass cqual, but
sparse, too.

> How is cqual going to handle all of the tty drivers which can have a
> pointer be either a userspace pointer, or a kernel pointer depending on
> the value of another paramater in a function?

I think all these functions should be changed to take two pointers, only
one of which is allowed to be non-NULL.  Then the flag can go away.  I
hope to submit a patch to this effect in the future.  I think sparse
can't check these either, unless you insert casts between user/kernel. 
But inserting casts loses the benefits of the automatic verification,
since the casts could be wrong.

> If you want to change the kernel to user interface like this, I suggest
> you do this for 2.6 first, let's not disturb that interface during the
> 2.4 stable kernel series.
> 
> Want to re-do this patch against 2.6.0-test3?

Ok.  Here's a patch against 2.6.0-test3.  I didn't add the md
substructure to i2c_msg, since it would require changing lots of files
throughout the kernel.  If you think that's an important change, I'll do
it.  Otherwise, the patch is the same idea as before.

Oh, yeah.  This patch also fixes the mem leak, and includes the
single-copy_from_user optimization you guys talked about earlier, since
those haven't been merged into mainline linux yet.

> Actually, why not just create a i2cfs for stuff like this and get rid of
> the ioctl crap all together...  Almost no one uses this (as is evident
> by a lack of 64 bit translation layer logic), and ioctls are a giant
> pain (as evidenced by the need for the 64 bit translation layer.)   It
> also forces users to program in languages that allow ioctls.

This sounds like a good idea, but my concern is just to get a kernel
that can be verified to have no user/kernel bugs.

> Oh, this should be discussed on lkml too, not just the sensors mailing
> list.

Done.  Thanks again for all your help.

Best,
Rob

--- drivers/i2c/i2c-dev.c.orig	Thu Aug 14 18:23:25 2003
+++ drivers/i2c/i2c-dev.c	Thu Aug 14 17:55:33 2003
@@ -180,6 +180,7 @@
 	struct i2c_rdwr_ioctl_data rdwr_arg;
 	struct i2c_smbus_ioctl_data data_arg;
 	union i2c_smbus_data temp;
+	struct i2c_msg *tmp_pa;
 	struct i2c_msg *rdwr_pa;
 	int i,datasize,res;
 	unsigned long funcs;
@@ -224,34 +225,47 @@
 		 * be sent at once */
 		if (rdwr_arg.nmsgs > 42)
 			return -EINVAL;
+
+		tmp_pa = (struct i2c_msg *)
+			kmalloc(rdwr_arg.nmsgs * sizeof(struct i2c_msg), 
+			GFP_KERNEL);
+
+		if (tmp_pa == NULL) return -ENOMEM;
+
+		if(copy_from_user(tmp_pa, rdwr_arg.msgs,
+				  rdwr_arg.nmsgs * sizeof(struct i2c_msg))) {
+			kfree(tmp_pa);
+			res = -EFAULT;
+		}
 		
 		rdwr_pa = (struct i2c_msg *)
 			kmalloc(rdwr_arg.nmsgs * sizeof(struct i2c_msg), 
 			GFP_KERNEL);
 
-		if (rdwr_pa == NULL) return -ENOMEM;
+		if (rdwr_pa == NULL) {
+			kfree(tmp_pa);
+			return -ENOMEM;
+		}
 
 		res = 0;
 		for( i=0; i<rdwr_arg.nmsgs; i++ ) {
-		    	if(copy_from_user(&(rdwr_pa[i]),
-					&(rdwr_arg.msgs[i]),
-					sizeof(rdwr_pa[i]))) {
-			        res = -EFAULT;
-				break;
-			}
 			/* Limit the size of the message to a sane amount */
-			if (rdwr_pa[i].len > 8192) {
+			if (tmp_pa[i].len > 8192) {
 				res = -EINVAL;
 				break;
 			}
+			rdwr_pa[i].addr = tmp_pa[i].addr;
+			rdwr_pa[i].flags = tmp_pa[i].flags;
+			rdwr_pa[i].len = tmp_pa[i].flags;
 			rdwr_pa[i].buf = kmalloc(rdwr_pa[i].len, GFP_KERNEL);
 			if(rdwr_pa[i].buf == NULL) {
 				res = -ENOMEM;
 				break;
 			}
 			if(copy_from_user(rdwr_pa[i].buf,
-				rdwr_arg.msgs[i].buf,
+				tmp_pa[i].buf,
 				rdwr_pa[i].len)) {
+				++i; /* Needs to be kfreed too */
 			    	res = -EFAULT;
 				break;
 			}
@@ -261,6 +275,7 @@
 			for (j = 0; j < i; ++j)
 				kfree(rdwr_pa[j].buf);
 			kfree(rdwr_pa);
+			kfree(tmp_pa);
 			return res;
 		}
 		if (!res) {
@@ -271,7 +286,7 @@
 		while(i-- > 0) {
 			if( res>=0 && (rdwr_pa[i].flags & I2C_M_RD)) {
 				if(copy_to_user(
-					rdwr_arg.msgs[i].buf,
+					tmp_pa[i].buf,
 					rdwr_pa[i].buf,
 					rdwr_pa[i].len)) {
 					res = -EFAULT;
@@ -280,6 +295,7 @@
 			kfree(rdwr_pa[i].buf);
 		}
 		kfree(rdwr_pa);
+		kfree(tmp_pa);
 		return res;
 
 	case I2C_SMBUS:

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Greg KH]

On Thu, Aug 14, 2003 at 07:01:34PM -0700, Robert T. Johnson wrote:
> On Thu, 2003-08-14 at 12:09, Greg KH wrote:
> > Hm, much like Linus's sparse does already?  :)
> 
> Yes, but cqual needs fewer annotations (see below).
> 
> > His checker missed the 2.6 version of this, for some reason, I haven't
> > taken the time to figure out why.
> 
> Currently, sparse silently ignores missing annotations.  Since i2c-dev.c
> is not extensively annotated, it missed this bug.

i2c-dev.c is annotated in 2.6.  Did I miss anything that needs to be
marked as such?

> Also, cqual is more flexible than sparse.  For example, i2c-dev.c wants
> to use some i2c_msg structures to hold user bufs, and some to hold
> kernel bufs.  cqual handles this automatically, but sparse cannot at
> all.  To get i2c-dev.c to work with sparse, you'd need to declare two
> new types, "struct kernel_i2c_msg" and "struct user_i2c_msg", and change
> every instance of i2c_msg to be one or the other.

That's something that will be necessary anyway, if we want to get this
to ever work on a 64 bit processor running with a 32 bit userspace
(amd64, ppc64, sparc64, etc.)

> > How is cqual going to handle all of the tty drivers which can have a
> > pointer be either a userspace pointer, or a kernel pointer depending on
> > the value of another paramater in a function?
> 
> I think all these functions should be changed to take two pointers, only
> one of which is allowed to be non-NULL.  Then the flag can go away.  I
> hope to submit a patch to this effect in the future.  I think sparse
> can't check these either, unless you insert casts between user/kernel. 
> But inserting casts loses the benefits of the automatic verification,
> since the casts could be wrong.

Hm, how about just fixing the tty core to always pass in kernel buffers?
That would fix the "problem" in one place :)

Anyway, that's a 2.7 change that has been on my list of things to do for
a while...

> Ok.  Here's a patch against 2.6.0-test3.  I didn't add the md
> substructure to i2c_msg, since it would require changing lots of files
> throughout the kernel.  If you think that's an important change, I'll do
> it.  Otherwise, the patch is the same idea as before.
> 
> Oh, yeah.  This patch also fixes the mem leak, and includes the
> single-copy_from_user optimization you guys talked about earlier, since
> those haven't been merged into mainline linux yet.

Hm, I had already applied your patch, so this one doesn't apply.  Care
to re-do it against 2.6.0-test4 whenever that comes out?

thanks,

greg k-h

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Robert T. Johnson]

On Fri, 2003-08-15 at 14:13, Greg KH wrote:
> i2c-dev.c is annotated in 2.6.  Did I miss anything that needs to be
> marked as such?

For this particular bug (before all the patches started flying around),
you'd have to add a kernel annotation to the "struct i2c_msg" field
buf.  But you still have the problem that sparse silently ignores
missing annotations, so you can never tell if you've missed something
important.  Cqual infers the annotations on its own, so you never have
to worry that some might be missing or wrong.

That's also how we get away with just ~200 annotations.  From these
"seed" annotations, cqual figures out everything else on its own.

> > I think all these functions should be changed to take two pointers, only
> > one of which is allowed to be non-NULL.  Then the flag can go away.  I
> > hope to submit a patch to this effect in the future.  I think sparse
> > can't check these either, unless you insert casts between user/kernel. 
> > But inserting casts loses the benefits of the automatic verification,
> > since the casts could be wrong.
> 
> Hm, how about just fixing the tty core to always pass in kernel buffers?
> That would fix the "problem" in one place :)

That's a good idea, but is that possible?  In other words, can the tty
core always tell how much to copy into kernel space?  The solution I
propose is a very simple change that fits easily into the current
architecture.

> Hm, I had already applied your patch, so this one doesn't apply.  Care
> to re-do it against 2.6.0-test4 whenever that comes out?

I was afraid that might happen.  I'll do a patch against test4 when it's
available.  Thanks for your suggestions.

Best,
Rob

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Greg KH]

On Fri, Aug 15, 2003 at 03:17:25PM -0700, Robert T. Johnson wrote:
> On Fri, 2003-08-15 at 14:13, Greg KH wrote:
> > i2c-dev.c is annotated in 2.6.  Did I miss anything that needs to be
> > marked as such?
> 
> For this particular bug (before all the patches started flying around),
> you'd have to add a kernel annotation to the "struct i2c_msg" field
> buf.

Look at 2.6, that annotatation is already there.

> But you still have the problem that sparse silently ignores
> missing annotations, so you can never tell if you've missed something
> important.  Cqual infers the annotations on its own, so you never have
> to worry that some might be missing or wrong.

Nice, is cqual released somewhere so that we can compare it and start
using it, like we already use sparse?

> > Hm, how about just fixing the tty core to always pass in kernel buffers?
> > That would fix the "problem" in one place :)
> 
> That's a good idea, but is that possible?  In other words, can the tty
> core always tell how much to copy into kernel space?

Yes it is, one of the paramaters in those functions is the size of the
buffer :)

> The solution I propose is a very simple change that fits easily into
> the current architecture.

Not really, you still are saying that all tty drivers need to be
changed, and new logic added to handle the additional paramater.  With
my proposed change, all drivers also have to be changed, but logic and
paramaters gets to be removed, making it harder for tty driver authors
to get things wrong.

thanks,

greg k-h

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Robert T. Johnson]

On Fri, 2003-08-15 at 16:51, Greg KH wrote:
> On Fri, Aug 15, 2003 at 03:17:25PM -0700, Robert T. Johnson wrote:
> > For this particular bug (before all the patches started flying around),
> > you'd have to add a kernel annotation to the "struct i2c_msg" field
> > buf.
> 
> Look at 2.6, that annotatation is already there.

I just double-checked my copy of linux-2.6.0-test3, and I don't see it. 
Just to make sure we're talking about the same thing, I'm looking at
include/linux/i2c.h:402, i.e. the definition of field buf in struct
i2c_msg.

Now I see you have the msgs field of i2c_rdwr_ioctl_arg annotated as
__user.  That should've generated a warning from sparse.  Looks like a
bug in sparse to me.

> Nice, is cqual released somewhere so that we can compare it and start
> using it, like we already use sparse?

I just discussed it with the other developers, and we'll work on getting
a release out in the next week or so.  It still has rough edges, but
feedback from kernel developers like yourself will be invaluable.

> Yes it is, one of the paramaters in those functions is the size of the
> buffer :)

Oh.  Now I'm sold on your solution.  Thanks for pointing that out.

Best,
Rob

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Greg KH]

On Sun, Aug 17, 2003 at 05:54:36PM -0700, Robert T. Johnson wrote:
> On Fri, 2003-08-15 at 16:51, Greg KH wrote:
> > On Fri, Aug 15, 2003 at 03:17:25PM -0700, Robert T. Johnson wrote:
> > > For this particular bug (before all the patches started flying around),
> > > you'd have to add a kernel annotation to the "struct i2c_msg" field
> > > buf.
> > 
> > Look at 2.6, that annotatation is already there.
> 
> I just double-checked my copy of linux-2.6.0-test3, and I don't see it. 
> Just to make sure we're talking about the same thing, I'm looking at
> include/linux/i2c.h:402, i.e. the definition of field buf in struct
> i2c_msg.
> 
> Now I see you have the msgs field of i2c_rdwr_ioctl_arg annotated as
> __user.  That should've generated a warning from sparse.  Looks like a
> bug in sparse to me.

Hm, possibly.  Again, it's the "holds two different things depending on
the code path" problem.  No easy fix, even with annotation, except for
splitting the structures apart (which I recommend doing.)

> > Nice, is cqual released somewhere so that we can compare it and start
> > using it, like we already use sparse?
> 
> I just discussed it with the other developers, and we'll work on getting
> a release out in the next week or so.  It still has rough edges, but
> feedback from kernel developers like yourself will be invaluable.

Looking forward to it.

thanks,

greg k-h

CQual 0.99 Released: user/kernel pointer bug finding tool

[Robert T. Johnson]

Download: http://www.cs.umd.edu/~jfoster/cqual/.
Support:  cqual@cs.umd.edu.

CQual is a program verification tool that uses type-qualifier
inference to find bugs in C programs.  This release of CQual includes
support for finding user/kernel pointer bugs in the linux kernel.
CQual has already found user/kernel pointer bugs in source files that
passed through Linus' "sparse" tool without generating any warnings.
Our goals with this release are

- help kernel developers avoid user/kernel bugs
- get feedback from kernel developers for future CQual features

CQual's current main features are:

- It requires _very_ few annotations: we currently use only ~200
- It's sound: CQual verifies the _absence_ of user/kernel bugs
- It generates fewer false warnings than sparse.
- It's context-sensitve: CQual doesn't confuse different calls to the 
  same function.
- CQual allows different instances of a struct type to hold different 
  kinds of pointers (i.e. user vs. kernel)
- It can be easily extended to find new types of bugs by editing a 
  configuration file
- It's fast: CQual analyzes most files in 1-2 seconds.
- It integrates easily into the kernel checking process.

The distribution contains a KERNEL-QUICKSTART to help kernel
developers start finding user/kernel bugs quickly.  We look forward to
hearing your feedback.

CQual is currently developed by Jeff Foster, John Kodumal, Tachio
Terauchi, Rob Johnson, and many others.

Best,
Rob Johnson

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Robert T. Johnson]

On Fri, 2003-08-15 at 14:13, Greg KH wrote:
> Hm, I had already applied your patch, so this one doesn't apply.  Care
> to re-do it against 2.6.0-test4 whenever that comes out?

Here's the patch against 2.6.0-test4.  Just to remind everyone, this
patch doesn't fix any bugs (they're already fixed in 2.6.0-test3), it
just makes the code pass our static analysis tool, cqual, without
generating a warning.  Since finding and fixing these bugs is so tricky,
it seems worthwhile to have code which can be automatically verified to
be bug-free (at least w.r.t. user/kernel pointers).  That's what this
patch is about.  Let me know if you have any questions or comments. 
Thanks for everyone's help.

Best,
Rob

P.S. cqual is on its way -- we're working on documentation and
integrating it into the kernel build process.


--- drivers/i2c/i2c-dev.c.orig	Wed Aug 27 18:04:31 2003
+++ drivers/i2c/i2c-dev.c	Wed Aug 27 17:51:23 2003
@@ -181,7 +181,7 @@
 	struct i2c_smbus_ioctl_data data_arg;
 	union i2c_smbus_data temp;
 	struct i2c_msg *rdwr_pa;
-	u8 **data_ptrs;
+	struct i2c_msg *tmp_pa;
 	int i,datasize,res;
 	unsigned long funcs;
 
@@ -226,40 +226,44 @@
 		if (rdwr_arg.nmsgs > 42)
 			return -EINVAL;
 		
-		rdwr_pa = (struct i2c_msg *)
+		tmp_pa = (struct i2c_msg *)
 			kmalloc(rdwr_arg.nmsgs * sizeof(struct i2c_msg), 
 			GFP_KERNEL);
 
-		if (rdwr_pa == NULL) return -ENOMEM;
+		if (tmp_pa == NULL) return -ENOMEM;
 
-		if (copy_from_user(rdwr_pa, rdwr_arg.msgs,
+		if (copy_from_user(tmp_pa, rdwr_arg.msgs,
 				   rdwr_arg.nmsgs * sizeof(struct i2c_msg))) {
-			kfree(rdwr_pa);
+			kfree(tmp_pa);
 			return -EFAULT;
 		}
 
-		data_ptrs = (u8 **) kmalloc(rdwr_arg.nmsgs * sizeof(u8 *),
-					    GFP_KERNEL);
-		if (data_ptrs == NULL) {
-			kfree(rdwr_pa);
+		rdwr_pa = (struct i2c_msg *)
+			kmalloc(rdwr_arg.nmsgs * sizeof(struct i2c_msg), 
+			GFP_KERNEL);
+
+		if (rdwr_pa == NULL) {
+			kfree(tmp_pa);
 			return -ENOMEM;
 		}
 
 		res = 0;
 		for( i=0; i<rdwr_arg.nmsgs; i++ ) {
+			rdwr_pa[i].addr = tmp_pa[i].addr;
+			rdwr_pa[i].flags = tmp_pa[i].flags;
+			rdwr_pa[i].len = tmp_pa[i].len;
 			/* Limit the size of the message to a sane amount */
 			if (rdwr_pa[i].len > 8192) {
 				res = -EINVAL;
 				break;
 			}
-			data_ptrs[i] = rdwr_pa[i].buf;
 			rdwr_pa[i].buf = kmalloc(rdwr_pa[i].len, GFP_KERNEL);
 			if(rdwr_pa[i].buf == NULL) {
 				res = -ENOMEM;
 				break;
 			}
 			if(copy_from_user(rdwr_pa[i].buf,
-				data_ptrs[i],
+				tmp_pa[i].buf,
 				rdwr_pa[i].len)) {
 					++i; /* Needs to be kfreed too */
 					res = -EFAULT;
@@ -270,8 +274,8 @@
 			int j;
 			for (j = 0; j < i; ++j)
 				kfree(rdwr_pa[j].buf);
-			kfree(data_ptrs);
 			kfree(rdwr_pa);
+			kfree(tmp_pa);
 			return res;
 		}
 
@@ -281,7 +285,7 @@
 		while(i-- > 0) {
 			if( res>=0 && (rdwr_pa[i].flags & I2C_M_RD)) {
 				if(copy_to_user(
-					data_ptrs[i],
+					tmp_pa[i].buf,
 					rdwr_pa[i].buf,
 					rdwr_pa[i].len)) {
 					res = -EFAULT;
@@ -289,8 +293,8 @@
 			}
 			kfree(rdwr_pa[i].buf);
 		}
-		kfree(data_ptrs);
 		kfree(rdwr_pa);
+		kfree(tmp_pa);
 		return res;
 
 	case I2C_SMBUS:

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Jean Delvare]

> Here's the patch against 2.6.0-test4.  Just to remind everyone, this
> patch doesn't fix any bugs (they're already fixed in 2.6.0-test3), it
> just makes the code pass our static analysis tool, cqual, without
> generating a warning.  Since finding and fixing these bugs is so
> tricky, it seems worthwhile to have code which can be automatically
> verified to be bug-free (at least w.r.t. user/kernel pointers). 
> That's what this patch is about.  Let me know if you have any
> questions or comments. Thanks for everyone's help.

If I read the patch correctly, this is basically a kind of reversal to
your original patch, before Sergey and I changed it?

-- 
Jean Delvare
http://www.ensicaen.ismra.fr/~delvare/

Re: [PATCH 2.4] i2c-dev user/kernel bug and mem leak

[Robert T. Johnson]

On Fri, 2003-08-29 at 09:21, Jean Delvare wrote:
> > Here's the patch against 2.6.0-test4.  Just to remind everyone, this
> > patch doesn't fix any bugs (they're already fixed in 2.6.0-test3), it
> > just makes the code pass our static analysis tool, cqual, without
> > generating a warning.  Since finding and fixing these bugs is so
> > tricky, it seems worthwhile to have code which can be automatically
> > verified to be bug-free (at least w.r.t. user/kernel pointers). 
> > That's what this patch is about.  Let me know if you have any
> > questions or comments. Thanks for everyone's help.
> 
> If I read the patch correctly, this is basically a kind of reversal to
> your original patch, before Sergey and I changed it?

You're absolutely right.  The patch is purely "aesthetic", in the sense
that it gets the code to pass cqual without generating any warnings.  I
understand the code may seem slightly odd, but it can be _automatically_
verified to have no user/kernel bugs.  That's its real advantage.

Thanks for looking at the patch so carefully, and for your comments.

Best,
Rob