From: gechao <gechao@greatwall.com.cn>

Fix the bug of terminal fifo buffer overflow with UINT8 type.

typedef struct {
  UINT8 Head;
  UINT8 Tail;
  UINT8 Data[RAW_FIFO_MAX_NUMBER + 1];
} RAW_DATA_FIFO;
RAW_FIFO_MAX_NUMBER is 256.
the data buffer size is 257 (Index from 0 to 256), but the max value of
the index, Head or Tail (UINT8), is 255. That means the last data of the
data buffer would be always empty if we use Head/Tail to output/input the
data correctly.  And because of the incorrect buffer size the FIFO full
check "((Tail + 1) % (RAW_FIFO_MAX_NUMBER + 1)) == Head" would never meet.

Signed-off-by: gechao <gechao@greatwall.com.cn>
---
 MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h b/MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h
index 378ace13ce..360e58e847 100644
--- a/MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h
+++ b/MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h
@@ -37,7 +37,7 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 #include <Library/BaseLib.h>
 
 
-#define RAW_FIFO_MAX_NUMBER 256
+#define RAW_FIFO_MAX_NUMBER 255
 #define FIFO_MAX_NUMBER     128
 
 typedef struct {
-- 
2.25.1



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There is no need to add [BUG] in the title. I would remove it when I create the PR.
If you want to have a record for this bug, you can edit a Bugzilla and add the link in the commit message.
Beside of that, Reviewed-by: Zhichao Gao <zhichao.gao@intel.com>

Thanks,
Zhichao

> -----Original Message-----
> From: gechao@greatwall.com.cn <gechao@greatwall.com.cn>
> Sent: Thursday, January 14, 2021 11:23 AM
> To: Gao, Zhichao <zhichao.gao@intel.com>
> Cc: devel@edk2.groups.io; Ni, Ray <ray.ni@intel.com>; gechao
> <gechao@greatwall.com.cn>
> Subject: [PATCH] MdeModulePkg/TerminalDxe [BUG]: Terminal fifo buffer
> overflow.
> 
> From: gechao <gechao@greatwall.com.cn>
> 
> Fix the bug of terminal fifo buffer overflow with UINT8 type.
> 
> typedef struct {
>   UINT8 Head;
>   UINT8 Tail;
>   UINT8 Data[RAW_FIFO_MAX_NUMBER + 1];
> } RAW_DATA_FIFO;
> RAW_FIFO_MAX_NUMBER is 256.
> the data buffer size is 257 (Index from 0 to 256), but the max value of the index,
> Head or Tail (UINT8), is 255. That means the last data of the data buffer would be
> always empty if we use Head/Tail to output/input the data correctly.  And
> because of the incorrect buffer size the FIFO full check "((Tail + 1) %
> (RAW_FIFO_MAX_NUMBER + 1)) == Head" would never meet.
> 
> Signed-off-by: gechao <gechao@greatwall.com.cn>
> ---
>  MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h
> b/MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h
> index 378ace13ce..360e58e847 100644
> --- a/MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h
> +++ b/MdeModulePkg/Universal/Console/TerminalDxe/Terminal.h
> @@ -37,7 +37,7 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
>  #include <Library/BaseLib.h>  -#define RAW_FIFO_MAX_NUMBER 256+#define
> RAW_FIFO_MAX_NUMBER 255 #define FIFO_MAX_NUMBER     128  typedef
> struct {--
> 2.25.1



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