[PATCH] MdePkg/SafeString: Directly return when length of source string is 0

[PATCH] MdePkg/SafeString: Directly return when length of source string is 0

[Ruiyu Ni]

Today's implementation of [Ascii]StrnCpyS/[Ascii]StrnCatS doesn't
directly return the the length of source string is 0.

When length of source string is 0, it means the Source points to
a memory that shouldn't be deferenced at all.
So it's not proper to call StrnLenS() in such situation.
In a pool guard enabled environment, when using shell to edit an
existing file which contains empty line, the page fault is met.

The patch fixes the four library functions to align to the behavior
of non-safe version: directly return when length of source string
is 0.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
---
 MdePkg/Library/BaseLib/SafeString.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/MdePkg/Library/BaseLib/SafeString.c b/MdePkg/Library/BaseLib/SafeString.c
index 68c33e9b7b..fed818ef33 100644
--- a/MdePkg/Library/BaseLib/SafeString.c
+++ b/MdePkg/Library/BaseLib/SafeString.c
@@ -1,7 +1,7 @@
 /** @file
   Safe String functions.
 
-  Copyright (c) 2014 - 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2014 - 2018, Intel Corporation. All rights reserved.<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
   which accompanies this distribution.  The full text of the license may be found at
@@ -317,6 +317,10 @@ StrnCpyS (
 {
   UINTN            SourceLen;
 
+  if (Length == 0) {
+    return RETURN_SUCCESS;
+  }
+
   ASSERT (((UINTN) Destination & BIT0) == 0);
   ASSERT (((UINTN) Source & BIT0) == 0);
 
@@ -515,6 +519,10 @@ StrnCatS (
   UINTN               CopyLen;
   UINTN               SourceLen;
 
+  if (Length == 0) {
+    return RETURN_SUCCESS;
+  }
+
   ASSERT (((UINTN) Destination & BIT0) == 0);
   ASSERT (((UINTN) Source & BIT0) == 0);
 
@@ -1894,6 +1902,10 @@ AsciiStrnCpyS (
 {
   UINTN            SourceLen;
 
+  if (Length == 0) {
+    return RETURN_SUCCESS;
+  }
+
   //
   // 1. Neither Destination nor Source shall be a null pointer.
   //
@@ -2082,6 +2094,10 @@ AsciiStrnCatS (
   UINTN               CopyLen;
   UINTN               SourceLen;
 
+  if (Length == 0) {
+    return RETURN_SUCCESS;
+  }
+
   //
   // Let CopyLen denote the value DestMax - AsciiStrnLenS(Destination, DestMax) upon entry to AsciiStrnCatS.
   //
-- 
2.16.1.windows.1

Re: [PATCH] MdePkg/SafeString: Directly return when length of source string is 0

[Laszlo Ersek]

On 02/02/18 11:47, Ruiyu Ni wrote:
> Today's implementation of [Ascii]StrnCpyS/[Ascii]StrnCatS doesn't
> directly return the the length of source string is 0.
> 
> When length of source string is 0, it means the Source points to
> a memory that shouldn't be deferenced at all.
> So it's not proper to call StrnLenS() in such situation.
> In a pool guard enabled environment, when using shell to edit an
> existing file which contains empty line, the page fault is met.
> 
> The patch fixes the four library functions to align to the behavior
> of non-safe version: directly return when length of source string
> is 0.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> ---
>  MdePkg/Library/BaseLib/SafeString.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/MdePkg/Library/BaseLib/SafeString.c b/MdePkg/Library/BaseLib/SafeString.c
> index 68c33e9b7b..fed818ef33 100644
> --- a/MdePkg/Library/BaseLib/SafeString.c
> +++ b/MdePkg/Library/BaseLib/SafeString.c
> @@ -1,7 +1,7 @@
>  /** @file
>    Safe String functions.
>  
> -  Copyright (c) 2014 - 2017, Intel Corporation. All rights reserved.<BR>
> +  Copyright (c) 2014 - 2018, Intel Corporation. All rights reserved.<BR>
>    This program and the accompanying materials
>    are licensed and made available under the terms and conditions of the BSD License
>    which accompanies this distribution.  The full text of the license may be found at
> @@ -317,6 +317,10 @@ StrnCpyS (
>  {
>    UINTN            SourceLen;
>  
> +  if (Length == 0) {
> +    return RETURN_SUCCESS;
> +  }
> +
>    ASSERT (((UINTN) Destination & BIT0) == 0);
>    ASSERT (((UINTN) Source & BIT0) == 0);
>  
> @@ -515,6 +519,10 @@ StrnCatS (
>    UINTN               CopyLen;
>    UINTN               SourceLen;
>  
> +  if (Length == 0) {
> +    return RETURN_SUCCESS;
> +  }
> +
>    ASSERT (((UINTN) Destination & BIT0) == 0);
>    ASSERT (((UINTN) Source & BIT0) == 0);
>  
> @@ -1894,6 +1902,10 @@ AsciiStrnCpyS (
>  {
>    UINTN            SourceLen;
>  
> +  if (Length == 0) {
> +    return RETURN_SUCCESS;
> +  }
> +
>    //
>    // 1. Neither Destination nor Source shall be a null pointer.
>    //
> @@ -2082,6 +2094,10 @@ AsciiStrnCatS (
>    UINTN               CopyLen;
>    UINTN               SourceLen;
>  
> +  if (Length == 0) {
> +    return RETURN_SUCCESS;
> +  }
> +
>    //
>    // Let CopyLen denote the value DestMax - AsciiStrnLenS(Destination, DestMax) upon entry to AsciiStrnCatS.
>    //
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Re: [PATCH] MdePkg/SafeString: Directly return when length of source string is 0

[Wang, Jian J]

Reviewed-by: Jian J Wang <jian.j.wang@intel.com>

> -----Original Message-----
> From: Ni, Ruiyu
> Sent: Friday, February 02, 2018 6:48 PM
> To: edk2-devel@lists.01.org
> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Gao, Liming <liming.gao@intel.com>;
> Wang, Jian J <jian.j.wang@intel.com>
> Subject: [PATCH] MdePkg/SafeString: Directly return when length of source
> string is 0
> 
> Today's implementation of [Ascii]StrnCpyS/[Ascii]StrnCatS doesn't
> directly return the the length of source string is 0.
> 
> When length of source string is 0, it means the Source points to
> a memory that shouldn't be deferenced at all.
> So it's not proper to call StrnLenS() in such situation.
> In a pool guard enabled environment, when using shell to edit an
> existing file which contains empty line, the page fault is met.
> 
> The patch fixes the four library functions to align to the behavior
> of non-safe version: directly return when length of source string
> is 0.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> ---
>  MdePkg/Library/BaseLib/SafeString.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/MdePkg/Library/BaseLib/SafeString.c
> b/MdePkg/Library/BaseLib/SafeString.c
> index 68c33e9b7b..fed818ef33 100644
> --- a/MdePkg/Library/BaseLib/SafeString.c
> +++ b/MdePkg/Library/BaseLib/SafeString.c
> @@ -1,7 +1,7 @@
>  /** @file
>    Safe String functions.
> 
> -  Copyright (c) 2014 - 2017, Intel Corporation. All rights reserved.<BR>
> +  Copyright (c) 2014 - 2018, Intel Corporation. All rights reserved.<BR>
>    This program and the accompanying materials
>    are licensed and made available under the terms and conditions of the BSD
> License
>    which accompanies this distribution.  The full text of the license may be found
> at
> @@ -317,6 +317,10 @@ StrnCpyS (
>  {
>    UINTN            SourceLen;
> 
> +  if (Length == 0) {
> +    return RETURN_SUCCESS;
> +  }
> +
>    ASSERT (((UINTN) Destination & BIT0) == 0);
>    ASSERT (((UINTN) Source & BIT0) == 0);
> 
> @@ -515,6 +519,10 @@ StrnCatS (
>    UINTN               CopyLen;
>    UINTN               SourceLen;
> 
> +  if (Length == 0) {
> +    return RETURN_SUCCESS;
> +  }
> +
>    ASSERT (((UINTN) Destination & BIT0) == 0);
>    ASSERT (((UINTN) Source & BIT0) == 0);
> 
> @@ -1894,6 +1902,10 @@ AsciiStrnCpyS (
>  {
>    UINTN            SourceLen;
> 
> +  if (Length == 0) {
> +    return RETURN_SUCCESS;
> +  }
> +
>    //
>    // 1. Neither Destination nor Source shall be a null pointer.
>    //
> @@ -2082,6 +2094,10 @@ AsciiStrnCatS (
>    UINTN               CopyLen;
>    UINTN               SourceLen;
> 
> +  if (Length == 0) {
> +    return RETURN_SUCCESS;
> +  }
> +
>    //
>    // Let CopyLen denote the value DestMax - AsciiStrnLenS(Destination,
> DestMax) upon entry to AsciiStrnCatS.
>    //
> --
> 2.16.1.windows.1

Re: [PATCH] MdePkg/SafeString: Directly return when length of source string is 0

[Yao, Jiewen]

Thanks to catch this.

The root-cause of the failure is below line:

  SourceLen = StrnLenS (Source, DestMax);

We should only limit the Source string access within Length, not DestMax, if Length is smaller than DestMax.

0 is just one special case. Length might be 1, 2, or 3 and it triggers same failure.

So only checking 0 is not enough.

Reviewed the code with Ruiyu. We think using below check seems better way to handle all cases.

  SourceLen = StrnLenS (Source, MIN(DestMax, Length));

The check for 0 is not needed.

Thank you
Yao Jiewen

> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Friday, February 2, 2018 9:43 PM
> To: Ni, Ruiyu <ruiyu.ni@intel.com>; edk2-devel@lists.01.org
> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Gao, Liming <liming.gao@intel.com>
> Subject: Re: [edk2] [PATCH] MdePkg/SafeString: Directly return when length of
> source string is 0
> 
> On 02/02/18 11:47, Ruiyu Ni wrote:
> > Today's implementation of [Ascii]StrnCpyS/[Ascii]StrnCatS doesn't
> > directly return the the length of source string is 0.
> >
> > When length of source string is 0, it means the Source points to
> > a memory that shouldn't be deferenced at all.
> > So it's not proper to call StrnLenS() in such situation.
> > In a pool guard enabled environment, when using shell to edit an
> > existing file which contains empty line, the page fault is met.
> >
> > The patch fixes the four library functions to align to the behavior
> > of non-safe version: directly return when length of source string
> > is 0.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
> > Cc: Jiewen Yao <jiewen.yao@intel.com>
> > Cc: Liming Gao <liming.gao@intel.com>
> > Cc: Jian J Wang <jian.j.wang@intel.com>
> > ---
> >  MdePkg/Library/BaseLib/SafeString.c | 18 +++++++++++++++++-
> >  1 file changed, 17 insertions(+), 1 deletion(-)
> >
> > diff --git a/MdePkg/Library/BaseLib/SafeString.c
> b/MdePkg/Library/BaseLib/SafeString.c
> > index 68c33e9b7b..fed818ef33 100644
> > --- a/MdePkg/Library/BaseLib/SafeString.c
> > +++ b/MdePkg/Library/BaseLib/SafeString.c
> > @@ -1,7 +1,7 @@
> >  /** @file
> >    Safe String functions.
> >
> > -  Copyright (c) 2014 - 2017, Intel Corporation. All rights reserved.<BR>
> > +  Copyright (c) 2014 - 2018, Intel Corporation. All rights reserved.<BR>
> >    This program and the accompanying materials
> >    are licensed and made available under the terms and conditions of the BSD
> License
> >    which accompanies this distribution.  The full text of the license may be
> found at
> > @@ -317,6 +317,10 @@ StrnCpyS (
> >  {
> >    UINTN            SourceLen;
> >
> > +  if (Length == 0) {
> > +    return RETURN_SUCCESS;
> > +  }
> > +
> >    ASSERT (((UINTN) Destination & BIT0) == 0);
> >    ASSERT (((UINTN) Source & BIT0) == 0);
> >
> > @@ -515,6 +519,10 @@ StrnCatS (
> >    UINTN               CopyLen;
> >    UINTN               SourceLen;
> >
> > +  if (Length == 0) {
> > +    return RETURN_SUCCESS;
> > +  }
> > +
> >    ASSERT (((UINTN) Destination & BIT0) == 0);
> >    ASSERT (((UINTN) Source & BIT0) == 0);
> >
> > @@ -1894,6 +1902,10 @@ AsciiStrnCpyS (
> >  {
> >    UINTN            SourceLen;
> >
> > +  if (Length == 0) {
> > +    return RETURN_SUCCESS;
> > +  }
> > +
> >    //
> >    // 1. Neither Destination nor Source shall be a null pointer.
> >    //
> > @@ -2082,6 +2094,10 @@ AsciiStrnCatS (
> >    UINTN               CopyLen;
> >    UINTN               SourceLen;
> >
> > +  if (Length == 0) {
> > +    return RETURN_SUCCESS;
> > +  }
> > +
> >    //
> >    // Let CopyLen denote the value DestMax - AsciiStrnLenS(Destination,
> DestMax) upon entry to AsciiStrnCatS.
> >    //
> >
> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Re: [PATCH] MdePkg/SafeString: Directly return when length of source string is 0

[Ni, Ruiyu]

On 2/5/2018 11:55 AM, Yao, Jiewen wrote:
> Thanks to catch this.
> 
> The root-cause of the failure is below line:
> 
>    SourceLen = StrnLenS (Source, DestMax);
> 
> We should only limit the Source string access within Length, not DestMax, if Length is smaller than DestMax.
> 
> 0 is just one special case. Length might be 1, 2, or 3 and it triggers same failure.
> 
> So only checking 0 is not enough.
> 
> Reviewed the code with Ruiyu. We think using below check seems better way to handle all cases.
> 
>    SourceLen = StrnLenS (Source, MIN(DestMax, Length));
> 
> The check for 0 is not needed.

Patch v2 is sent out.

> 
> Thank you
> Yao Jiewen
> 
>> -----Original Message-----
>> From: Laszlo Ersek [mailto:lersek@redhat.com]
>> Sent: Friday, February 2, 2018 9:43 PM
>> To: Ni, Ruiyu <ruiyu.ni@intel.com>; edk2-devel@lists.01.org
>> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Gao, Liming <liming.gao@intel.com>
>> Subject: Re: [edk2] [PATCH] MdePkg/SafeString: Directly return when length of
>> source string is 0
>>
>> On 02/02/18 11:47, Ruiyu Ni wrote:
>>> Today's implementation of [Ascii]StrnCpyS/[Ascii]StrnCatS doesn't
>>> directly return the the length of source string is 0.
>>>
>>> When length of source string is 0, it means the Source points to
>>> a memory that shouldn't be deferenced at all.
>>> So it's not proper to call StrnLenS() in such situation.
>>> In a pool guard enabled environment, when using shell to edit an
>>> existing file which contains empty line, the page fault is met.
>>>
>>> The patch fixes the four library functions to align to the behavior
>>> of non-safe version: directly return when length of source string
>>> is 0.
>>>
>>> Contributed-under: TianoCore Contribution Agreement 1.1
>>> Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>> Cc: Liming Gao <liming.gao@intel.com>
>>> Cc: Jian J Wang <jian.j.wang@intel.com>
>>> ---
>>>   MdePkg/Library/BaseLib/SafeString.c | 18 +++++++++++++++++-
>>>   1 file changed, 17 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/MdePkg/Library/BaseLib/SafeString.c
>> b/MdePkg/Library/BaseLib/SafeString.c
>>> index 68c33e9b7b..fed818ef33 100644
>>> --- a/MdePkg/Library/BaseLib/SafeString.c
>>> +++ b/MdePkg/Library/BaseLib/SafeString.c
>>> @@ -1,7 +1,7 @@
>>>   /** @file
>>>     Safe String functions.
>>>
>>> -  Copyright (c) 2014 - 2017, Intel Corporation. All rights reserved.<BR>
>>> +  Copyright (c) 2014 - 2018, Intel Corporation. All rights reserved.<BR>
>>>     This program and the accompanying materials
>>>     are licensed and made available under the terms and conditions of the BSD
>> License
>>>     which accompanies this distribution.  The full text of the license may be
>> found at
>>> @@ -317,6 +317,10 @@ StrnCpyS (
>>>   {
>>>     UINTN            SourceLen;
>>>
>>> +  if (Length == 0) {
>>> +    return RETURN_SUCCESS;
>>> +  }
>>> +
>>>     ASSERT (((UINTN) Destination & BIT0) == 0);
>>>     ASSERT (((UINTN) Source & BIT0) == 0);
>>>
>>> @@ -515,6 +519,10 @@ StrnCatS (
>>>     UINTN               CopyLen;
>>>     UINTN               SourceLen;
>>>
>>> +  if (Length == 0) {
>>> +    return RETURN_SUCCESS;
>>> +  }
>>> +
>>>     ASSERT (((UINTN) Destination & BIT0) == 0);
>>>     ASSERT (((UINTN) Source & BIT0) == 0);
>>>
>>> @@ -1894,6 +1902,10 @@ AsciiStrnCpyS (
>>>   {
>>>     UINTN            SourceLen;
>>>
>>> +  if (Length == 0) {
>>> +    return RETURN_SUCCESS;
>>> +  }
>>> +
>>>     //
>>>     // 1. Neither Destination nor Source shall be a null pointer.
>>>     //
>>> @@ -2082,6 +2094,10 @@ AsciiStrnCatS (
>>>     UINTN               CopyLen;
>>>     UINTN               SourceLen;
>>>
>>> +  if (Length == 0) {
>>> +    return RETURN_SUCCESS;
>>> +  }
>>> +
>>>     //
>>>     // Let CopyLen denote the value DestMax - AsciiStrnLenS(Destination,
>> DestMax) upon entry to AsciiStrnCatS.
>>>     //
>>>
>>
>> Reviewed-by: Laszlo Ersek <lersek@redhat.com>


-- 
Thanks,
Ray