[PATCH] staging: lustre: Remove VLA usage

[PATCH] staging: lustre: Remove VLA usage

[Kees Cook]

The kernel would like to remove all VLA usage. This switches to a
simple kasprintf() instead.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/staging/lustre/lustre/llite/xattr.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/lustre/lustre/llite/xattr.c b/drivers/staging/lustre/lustre/llite/xattr.c
index 532384c91447..aab4eab64289 100644
--- a/drivers/staging/lustre/lustre/llite/xattr.c
+++ b/drivers/staging/lustre/lustre/llite/xattr.c
@@ -87,7 +87,7 @@ ll_xattr_set_common(const struct xattr_handler *handler,
 		    const char *name, const void *value, size_t size,
 		    int flags)
 {
-	char fullname[strlen(handler->prefix) + strlen(name) + 1];
+	char *fullname;
 	struct ll_sb_info *sbi = ll_i2sbi(inode);
 	struct ptlrpc_request *req = NULL;
 	const char *pv = value;
@@ -141,10 +141,13 @@ ll_xattr_set_common(const struct xattr_handler *handler,
 			return -EPERM;
 	}
 
-	sprintf(fullname, "%s%s\n", handler->prefix, name);
+	fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name);
+	if (!fullname)
+		return -ENOMEM;
 	rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode),
 			 valid, fullname, pv, size, 0, flags,
 			 ll_i2suppgid(inode), &req);
+	kfree(fullname);
 	if (rc) {
 		if (rc == -EOPNOTSUPP && handler->flags == XATTR_USER_T) {
 			LCONSOLE_INFO("Disabling user_xattr feature because it is not supported on the server\n");
@@ -364,7 +367,7 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
 			       struct dentry *dentry, struct inode *inode,
 			       const char *name, void *buffer, size_t size)
 {
-	char fullname[strlen(handler->prefix) + strlen(name) + 1];
+	char *fullname;
 	struct ll_sb_info *sbi = ll_i2sbi(inode);
 #ifdef CONFIG_FS_POSIX_ACL
 	struct ll_inode_info *lli = ll_i2info(inode);
@@ -411,9 +414,13 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
 	if (handler->flags == XATTR_ACL_DEFAULT_T && !S_ISDIR(inode->i_mode))
 		return -ENODATA;
 #endif
-	sprintf(fullname, "%s%s\n", handler->prefix, name);
-	return ll_xattr_list(inode, fullname, handler->flags, buffer, size,
-			     OBD_MD_FLXATTR);
+	fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name);
+	if (!fullname)
+		return -ENOMEM;
+	rc = ll_xattr_list(inode, fullname, handler->flags, buffer, size,
+			   OBD_MD_FLXATTR);
+	kfree(fullname);
+	return rc;
 }
 
 static ssize_t ll_getxattr_lov(struct inode *inode, void *buf, size_t buf_size)
-- 
2.7.4


-- 
Kees Cook
Pixel Security

Re: [PATCH] staging: lustre: Remove VLA usage

[Tobin C. Harding]

On Tue, Mar 06, 2018 at 09:46:08PM -0800, Kees Cook wrote:
> The kernel would like to remove all VLA usage. This switches to a
> simple kasprintf() instead.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/staging/lustre/lustre/llite/xattr.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/staging/lustre/lustre/llite/xattr.c b/drivers/staging/lustre/lustre/llite/xattr.c
> index 532384c91447..aab4eab64289 100644
> --- a/drivers/staging/lustre/lustre/llite/xattr.c
> +++ b/drivers/staging/lustre/lustre/llite/xattr.c
> @@ -87,7 +87,7 @@ ll_xattr_set_common(const struct xattr_handler *handler,
>  		    const char *name, const void *value, size_t size,
>  		    int flags)
>  {
> -	char fullname[strlen(handler->prefix) + strlen(name) + 1];
> +	char *fullname;
>  	struct ll_sb_info *sbi = ll_i2sbi(inode);
>  	struct ptlrpc_request *req = NULL;
>  	const char *pv = value;
> @@ -141,10 +141,13 @@ ll_xattr_set_common(const struct xattr_handler *handler,
>  			return -EPERM;
>  	}
>  
> -	sprintf(fullname, "%s%s\n", handler->prefix, name);
> +	fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name);
> +	if (!fullname)
> +		return -ENOMEM;
>  	rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode),
>  			 valid, fullname, pv, size, 0, flags,
>  			 ll_i2suppgid(inode), &req);
> +	kfree(fullname);

This is cool.  We've had kasprintf() since 2007, who knew?!

thanks,
Tobin.
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Re: [PATCH] staging: lustre: Remove VLA usage

[Rasmus Villemoes]

On 2018-03-07 06:46, Kees Cook wrote:
> The kernel would like to remove all VLA usage. This switches to a
> simple kasprintf() instead.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/staging/lustre/lustre/llite/xattr.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/staging/lustre/lustre/llite/xattr.c b/drivers/staging/lustre/lustre/llite/xattr.c
> index 532384c91447..aab4eab64289 100644
> --- a/drivers/staging/lustre/lustre/llite/xattr.c
> +++ b/drivers/staging/lustre/lustre/llite/xattr.c
> @@ -87,7 +87,7 @@ ll_xattr_set_common(const struct xattr_handler *handler,
>  		    const char *name, const void *value, size_t size,
>  		    int flags)
>  {
> -	char fullname[strlen(handler->prefix) + strlen(name) + 1];
> +	char *fullname;
>  	struct ll_sb_info *sbi = ll_i2sbi(inode);
>  	struct ptlrpc_request *req = NULL;
>  	const char *pv = value;
> @@ -141,10 +141,13 @@ ll_xattr_set_common(const struct xattr_handler *handler,
>  			return -EPERM;
>  	}
>  
> -	sprintf(fullname, "%s%s\n", handler->prefix, name);

It's probably worth pointing out that this actually fixes an
unconditional buffer overflow: fullname only has room for the two
strings and the '\n', but vsnprintf() is told that the buffer has
infinite size (well, INT_MAX), so there should be plenty of room to
append the '\0' after the '\n'.

> +	fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name);
> +	if (!fullname)
> +		return -ENOMEM;
>  	rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode),
>  			 valid, fullname, pv, size, 0, flags,
>  			 ll_i2suppgid(inode), &req);
> +	kfree(fullname);
>  	if (rc) {
>  		if (rc == -EOPNOTSUPP && handler->flags == XATTR_USER_T) {
>  			LCONSOLE_INFO("Disabling user_xattr feature because it is not supported on the server\n");
> @@ -364,7 +367,7 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
>  			       struct dentry *dentry, struct inode *inode,
>  			       const char *name, void *buffer, size_t size)
>  {
> -	char fullname[strlen(handler->prefix) + strlen(name) + 1];
> +	char *fullname;
>  	struct ll_sb_info *sbi = ll_i2sbi(inode);
>  #ifdef CONFIG_FS_POSIX_ACL
>  	struct ll_inode_info *lli = ll_i2info(inode);
> @@ -411,9 +414,13 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
>  	if (handler->flags == XATTR_ACL_DEFAULT_T && !S_ISDIR(inode->i_mode))
>  		return -ENODATA;
>  #endif
> -	sprintf(fullname, "%s%s\n", handler->prefix, name);

Same here.

I'm a little surprised this hasn't been caugt by static analysis, I
thought gcc/coverity/smatch/whatnot had gotten pretty good at computing
the size of the output generated by a given format string with "known"
arguments and comparing to the size of the output buffer. Though of
course it does require the tool to be able to do symbolic manipulations,
in this case realizing that

outsize == strlen(x)+strlen(y)+1+1 > bufsize == strlen(x)+strlen(y)+1

Rasmus

Re: [PATCH] staging: lustre: Remove VLA usage

[Kees Cook]

On Wed, Mar 7, 2018 at 5:10 AM, Rasmus Villemoes
<rasmus.villemoes@prevas.dk> wrote:
> On 2018-03-07 06:46, Kees Cook wrote:
>> The kernel would like to remove all VLA usage. This switches to a
>> simple kasprintf() instead.
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> ---
>>  drivers/staging/lustre/lustre/llite/xattr.c | 19 +++++++++++++------
>>  1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/staging/lustre/lustre/llite/xattr.c b/drivers/staging/lustre/lustre/llite/xattr.c
>> index 532384c91447..aab4eab64289 100644
>> --- a/drivers/staging/lustre/lustre/llite/xattr.c
>> +++ b/drivers/staging/lustre/lustre/llite/xattr.c
>> @@ -87,7 +87,7 @@ ll_xattr_set_common(const struct xattr_handler *handler,
>>                   const char *name, const void *value, size_t size,
>>                   int flags)
>>  {
>> -     char fullname[strlen(handler->prefix) + strlen(name) + 1];
>> +     char *fullname;
>>       struct ll_sb_info *sbi = ll_i2sbi(inode);
>>       struct ptlrpc_request *req = NULL;
>>       const char *pv = value;
>> @@ -141,10 +141,13 @@ ll_xattr_set_common(const struct xattr_handler *handler,
>>                       return -EPERM;
>>       }
>>
>> -     sprintf(fullname, "%s%s\n", handler->prefix, name);
>
> It's probably worth pointing out that this actually fixes an
> unconditional buffer overflow: fullname only has room for the two
> strings and the '\n', but vsnprintf() is told that the buffer has
> infinite size (well, INT_MAX), so there should be plenty of room to
> append the '\0' after the '\n'.
>
>> +     fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name);
>> +     if (!fullname)
>> +             return -ENOMEM;
>>       rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode),
>>                        valid, fullname, pv, size, 0, flags,
>>                        ll_i2suppgid(inode), &req);
>> +     kfree(fullname);
>>       if (rc) {
>>               if (rc == -EOPNOTSUPP && handler->flags == XATTR_USER_T) {
>>                       LCONSOLE_INFO("Disabling user_xattr feature because it is not supported on the server\n");
>> @@ -364,7 +367,7 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
>>                              struct dentry *dentry, struct inode *inode,
>>                              const char *name, void *buffer, size_t size)
>>  {
>> -     char fullname[strlen(handler->prefix) + strlen(name) + 1];
>> +     char *fullname;
>>       struct ll_sb_info *sbi = ll_i2sbi(inode);
>>  #ifdef CONFIG_FS_POSIX_ACL
>>       struct ll_inode_info *lli = ll_i2info(inode);
>> @@ -411,9 +414,13 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
>>       if (handler->flags == XATTR_ACL_DEFAULT_T && !S_ISDIR(inode->i_mode))
>>               return -ENODATA;
>>  #endif
>> -     sprintf(fullname, "%s%s\n", handler->prefix, name);
>
> Same here.
>
> I'm a little surprised this hasn't been caugt by static analysis, I
> thought gcc/coverity/smatch/whatnot had gotten pretty good at computing
> the size of the output generated by a given format string with "known"
> arguments and comparing to the size of the output buffer. Though of
> course it does require the tool to be able to do symbolic manipulations,
> in this case realizing that
>
> outsize == strlen(x)+strlen(y)+1+1 > bufsize == strlen(x)+strlen(y)+1
>
> Rasmus

Oh yes, hah. I didn't even see the \n in the string. :P

So, both a VLA fix and a buffer over-run fix. Can I add your "Reviewed-by"? :)

-Kees

-- 
Kees Cook
Pixel Security
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Re: [PATCH] staging: lustre: Remove VLA usage

[Rasmus Villemoes]

On Wed, Mar 07 2018, Kees Cook <keescook@chromium.org> wrote:

> On Wed, Mar 7, 2018 at 5:10 AM, Rasmus Villemoes
> <rasmus.villemoes@prevas.dk> wrote:
>> On 2018-03-07 06:46, Kees Cook wrote:
>>> The kernel would like to remove all VLA usage. This switches to a
>>> simple kasprintf() instead.
>>>
>>
>> It's probably worth pointing out that this actually fixes an
>> unconditional buffer overflow: fullname only has room for the two
>> strings and the '\n', but vsnprintf() is told that the buffer has
>> infinite size (well, INT_MAX), so there should be plenty of room to
>> append the '\0' after the '\n'.
>>
>
> Oh yes, hah. I didn't even see the \n in the string. :P
>
> So, both a VLA fix and a buffer over-run fix. Can I add your "Reviewed-by"? :)

Sure,

Reviewed-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>

A nit, if you're resending anyway: can you move the "char *fullname"
declarations down a bit, to between pv,valid, and lli,rc, respectively?
That keeps the initialized and uninitialized variables nicely together
and ends up looking better.
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Re: [PATCH] staging: lustre: Remove VLA usage

[Dan Carpenter]

On Wed, Mar 07, 2018 at 02:10:41PM +0100, Rasmus Villemoes wrote:
> On 2018-03-07 06:46, Kees Cook wrote:
> > The kernel would like to remove all VLA usage. This switches to a
> > simple kasprintf() instead.
> > 
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  drivers/staging/lustre/lustre/llite/xattr.c | 19 +++++++++++++------
> >  1 file changed, 13 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/staging/lustre/lustre/llite/xattr.c b/drivers/staging/lustre/lustre/llite/xattr.c
> > index 532384c91447..aab4eab64289 100644
> > --- a/drivers/staging/lustre/lustre/llite/xattr.c
> > +++ b/drivers/staging/lustre/lustre/llite/xattr.c
> > @@ -87,7 +87,7 @@ ll_xattr_set_common(const struct xattr_handler *handler,
> >  		    const char *name, const void *value, size_t size,
> >  		    int flags)
> >  {
> > -	char fullname[strlen(handler->prefix) + strlen(name) + 1];
> > +	char *fullname;
> >  	struct ll_sb_info *sbi = ll_i2sbi(inode);
> >  	struct ptlrpc_request *req = NULL;
> >  	const char *pv = value;
> > @@ -141,10 +141,13 @@ ll_xattr_set_common(const struct xattr_handler *handler,
> >  			return -EPERM;
> >  	}
> >  
> > -	sprintf(fullname, "%s%s\n", handler->prefix, name);
> 
> It's probably worth pointing out that this actually fixes an
> unconditional buffer overflow: fullname only has room for the two
> strings and the '\n', but vsnprintf() is told that the buffer has
> infinite size (well, INT_MAX), so there should be plenty of room to
> append the '\0' after the '\n'.
> 
> > +	fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name);
> > +	if (!fullname)
> > +		return -ENOMEM;
> >  	rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode),
> >  			 valid, fullname, pv, size, 0, flags,
> >  			 ll_i2suppgid(inode), &req);
> > +	kfree(fullname);
> >  	if (rc) {
> >  		if (rc == -EOPNOTSUPP && handler->flags == XATTR_USER_T) {
> >  			LCONSOLE_INFO("Disabling user_xattr feature because it is not supported on the server\n");
> > @@ -364,7 +367,7 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
> >  			       struct dentry *dentry, struct inode *inode,
> >  			       const char *name, void *buffer, size_t size)
> >  {
> > -	char fullname[strlen(handler->prefix) + strlen(name) + 1];
> > +	char *fullname;
> >  	struct ll_sb_info *sbi = ll_i2sbi(inode);
> >  #ifdef CONFIG_FS_POSIX_ACL
> >  	struct ll_inode_info *lli = ll_i2info(inode);
> > @@ -411,9 +414,13 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
> >  	if (handler->flags == XATTR_ACL_DEFAULT_T && !S_ISDIR(inode->i_mode))
> >  		return -ENODATA;
> >  #endif
> > -	sprintf(fullname, "%s%s\n", handler->prefix, name);
> 
> Same here.
> 
> I'm a little surprised this hasn't been caugt by static analysis, I
> thought gcc/coverity/smatch/whatnot had gotten pretty good at computing
> the size of the output generated by a given format string with "known"
> arguments and comparing to the size of the output buffer. Though of
> course it does require the tool to be able to do symbolic manipulations,
> in this case realizing that
> 
> outsize == strlen(x)+strlen(y)+1+1 > bufsize == strlen(x)+strlen(y)+1

That kind of symbolic manipulation is crazy hard to do.

regards,
dan carpenter

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