Re: [Bug-wget] [PATCH] Small fix for limited number of strings (and potential garbage value) in arguments to concat_strings

[Pär Karlsson]

Whoops, I realised I failed on the GNU coding standards, please disregard
the last one; the patch below should be better.

My apologies :-/

/Pär

diff --git a/src/ChangeLog b/src/ChangeLog
index d5aeca0..87abd85 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2014-10-20     Pär Karlsson  <address@hidden>
+
+       * utils.c (concat_strings): got rid of double loop, cleaned up
potential
+       memory corruption if concat_strings was called with more than five
args
+
 2014-10-16  Tim Ruehsen  <address@hidden>

        * url.c (url_parse): little code cleanup
diff --git a/src/utils.c b/src/utils.c
index 78c282e..5f359e0 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -356,42 +356,36 @@ char *
 concat_strings (const char *str0, ...)
 {
   va_list args;
-  int saved_lengths[5];         /* inspired by Apache's apr_pstrcat */
   char *ret, *p;

   const char *next_str;
-  int total_length = 0;
-  size_t argcount;
+  size_t len;
+  size_t total_length = 0;
+  size_t charsize = sizeof (char);
+  size_t chunksize = 64;
+  size_t bufsize = 64;
+
+  p = ret = xmalloc (charsize * bufsize);

   /* Calculate the length of and allocate the resulting string. */

-  argcount = 0;
   va_start (args, str0);
   for (next_str = str0; next_str != NULL; next_str = va_arg (args, char *))
     {
-      int len = strlen (next_str);
-      if (argcount < countof (saved_lengths))
-        saved_lengths[argcount++] = len;
+      len = strlen (next_str);
+      if (len == 0)
+        continue;
       total_length += len;
-    }
-  va_end (args);
-  p = ret = xmalloc (total_length + 1);
-
-  /* Copy the strings into the allocated space. */
-
-  argcount = 0;
-  va_start (args, str0);
-  for (next_str = str0; next_str != NULL; next_str = va_arg (args, char *))
-    {
-      int len;
-      if (argcount < countof (saved_lengths))
-        len = saved_lengths[argcount++];
-      else
-        len = strlen (next_str);
+      if (total_length > bufsize)
+      {
+        bufsize += chunksize;
+        ret = xrealloc (ret, charsize * bufsize);
+      }
       memcpy (p, next_str, len);
       p += len;
     }
   va_end (args);
+  ret = xrealloc (ret, charsize * total_length + 1);
   *p = '\0';

   return ret;

2014-10-20 22:14 GMT+02:00 Pär Karlsson <address@hidden>:

> Thank you for your feedback and suggestions.
>
> I thought about this during the weekend and figured it could be done much
> more efficiently, by only looping through the arguments once. Also, I
> realized the the original version would have segfaulted if called with more
> than 5 args, since the destination memory never got allocated before the
> memcpy (in the current code, it never is, though!).
>
> I cleaned up the code according to the GNU coding standards as well. The
> test suite rolls with this, and I think it looks better (although the
> function is only really called in a handful of places in all of wget).
>
> Best regards,
>
> /Pär
>
> Patch below:
>
> diff --git a/src/ChangeLog b/src/ChangeLog
> index d5aeca0..87abd85 100644
> --- a/src/ChangeLog
> +++ b/src/ChangeLog
> @@ -1,3 +1,8 @@
> +2014-10-20     Pär Karlsson  <address@hidden>
> +
> +       * utils.c (concat_strings): got rid of double loop, cleaned up
> potential
> +       memory corruption if concat_strings was called with more than five
> args
> +
>  2014-10-16  Tim Ruehsen  <address@hidden>
>
>         * url.c (url_parse): little code cleanup
> diff --git a/src/utils.c b/src/utils.c
> index 78c282e..dbeb9fe 100644
> --- a/src/utils.c
> +++ b/src/utils.c
> @@ -356,42 +356,36 @@ char *
>  concat_strings (const char *str0, ...)
>  {
>    va_list args;
> -  int saved_lengths[5];         /* inspired by Apache's apr_pstrcat */
>    char *ret, *p;
>
>    const char *next_str;
> -  int total_length = 0;
> -  size_t argcount;
> +  size_t len;
> +  size_t total_length = 0;
> +  size_t charsize = sizeof (char);
> +  size_t chunksize = 64;
> +  size_t bufsize = 64;
> +
> +  p = ret = xmalloc (charsize * bufsize);
>
>    /* Calculate the length of and allocate the resulting string. */
>
> -  argcount = 0;
>    va_start (args, str0);
>    for (next_str = str0; next_str != NULL; next_str = va_arg (args, char
> *))
>      {
> -      int len = strlen (next_str);
> -      if (argcount < countof (saved_lengths))
> -        saved_lengths[argcount++] = len;
> +      len = strlen (next_str);
> +      if (len == 0) {
> +          continue;
> +      }
>        total_length += len;
> -    }
> -  va_end (args);
> -  p = ret = xmalloc (total_length + 1);
> -
> -  /* Copy the strings into the allocated space. */
> -
> -  argcount = 0;
> -  va_start (args, str0);
> -  for (next_str = str0; next_str != NULL; next_str = va_arg (args, char
> *))
> -    {
> -      int len;
> -      if (argcount < countof (saved_lengths))
> -        len = saved_lengths[argcount++];
> -      else
> -        len = strlen (next_str);
> +      if (total_length > bufsize) {
> +          bufsize += chunksize;
> +          ret = xrealloc (ret, charsize * bufsize);
> +      }
>        memcpy (p, next_str, len);
>        p += len;
>      }
>    va_end (args);
> +  ret = xrealloc (ret, charsize * total_length + 1);
>    *p = '\0';
>
>    return ret;
>
>
>
> 2014-10-19 16:16 GMT+02:00 Giuseppe Scrivano <address@hidden>:
>
>> Pär Karlsson <address@hidden> writes:
>>
>> > Hi, I fould a potential gotcha when playing with clang's code analysis
>> tool.
>> >
>> > The concat_strings function silently stopped counting string lengths
>> when
>> > given more than 5 arguments. clang warned about potential garbage
>> values in
>> > the saved_lengths array, so I redid it with this approach.
>> >
>> > All tests working ok with this patch.
>>
>> thanks for your contribution.  I've just few comments:
>>
>>
>> > commit 2d855670e0e1fbe578506b376cdd40b0e465d3ef
>> > Author: Pär Karlsson <address@hidden>
>> > Date:   Thu Oct 16 21:41:36 2014 +0200
>> >
>> >     Updated ChangeLog
>> >
>>
>> we usually update the changelog in the same commit that made the change,
>> so please squash these two commits into one.
>>
>> Also, it doesn't apply on current git master, as it seems to be based on
>> a old version of git from the ChangeLog file context, could you rebase
>> onto the master branch?
>>
>>
>> > diff --git a/src/utils.c b/src/utils.c
>> > index 78c282e..93c9ddc 100644
>> > --- a/src/utils.c
>> > +++ b/src/utils.c
>> > @@ -356,7 +356,8 @@ char *
>> >  concat_strings (const char *str0, ...)
>> >  {
>> >    va_list args;
>> > -  int saved_lengths[5];         /* inspired by Apache's apr_pstrcat */
>> > +  size_t psize = sizeof(int);
>>
>> please leave a space between sizeof and '(' as mandated by the GNU
>> coding standards.
>>
>> > +  int *saved_lengths = xmalloc (psize);
>> >    char *ret, *p;
>> >
>> >    const char *next_str;
>> > @@ -370,8 +371,8 @@ concat_strings (const char *str0, ...)
>> >    for (next_str = str0; next_str != NULL; next_str = va_arg (args,
>> char *))
>> >      {
>> >        int len = strlen (next_str);
>> > -      if (argcount < countof (saved_lengths))
>> > -        saved_lengths[argcount++] = len;
>> > +      saved_lengths[argcount++] = len;
>> > +      xrealloc(saved_lengths, psize * argcount);
>>
>> same here.
>>
>> >        total_length += len;
>> >      }
>> >    va_end (args);
>> > @@ -393,7 +394,7 @@ concat_strings (const char *str0, ...)
>> >      }
>> >    va_end (args);
>> >    *p = '\0';
>> > -
>> > +  free(saved_lengths);
>>
>> and here.
>>
>> Regards,
>> Giuseppe
>>
>
>