Re: [Qemu-devel] [PATCH 03/22] vmdk: relative_path: avoid buffer overrun

[Jim Meyering]

Kevin Wolf wrote:
> Am 09.05.2012 11:23, schrieb Jim Meyering:
>> From: Jim Meyering <address@hidden>
>>
>> strncpy does not guarantee NUL-termination.
>> Setting dest[n-1] = '\0' *before* calling strncpy(dest, src, n-1)
>> is a no-op.  Use pstrcpy to ensure NUL-termination, not strncpy.
>
> It's not, it would only be a no-op before strncpy(dest, src, n). But
> pstrcpy() is definitely nicer.
>
>> Signed-off-by: Jim Meyering <address@hidden>
>> ---
>>  block/vmdk.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/block/vmdk.c b/block/vmdk.c
>> index 18e9b4c..045e279 100644
>> --- a/block/vmdk.c
>> +++ b/block/vmdk.c
>> @@ -1319,8 +1319,7 @@ static int relative_path(char *dest, int dest_size,
>>          return -1;
>>      }
>>      if (path_is_absolute(target)) {
>> -        dest[dest_size - 1] = '\0';
>> -        strncpy(dest, target, dest_size - 1);
>> +        pstrcpy(dest, dest_size - 1, target);
>
> I think you mean pstrcpy(dest, dest_size, target).

Good points.  Thanks for the review.
Here's the corrected commit:

>From 78a367d846c95e84fddc971cbae544f24bc3455f Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Mon, 7 May 2012 12:46:02 +0200
Subject: [PATCH] vmdk: relative_path: use pstrcpy in place of strncpy

Avoid strncpy+manual-NUL-terminate.  Use pstrcpy instead.

Signed-off-by: Jim Meyering <address@hidden>
---
 block/vmdk.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/block/vmdk.c b/block/vmdk.c
index 18e9b4c..bfd7357 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1319,8 +1319,7 @@ static int relative_path(char *dest, int dest_size,
         return -1;
     }
     if (path_is_absolute(target)) {
-        dest[dest_size - 1] = '\0';
-        strncpy(dest, target, dest_size - 1);
+        pstrcpy(dest, dest_size, target);
         return 0;
     }
     while (base[i] == target[i]) {
--
1.7.10.1.487.ga3935e6