Re: [PATCH v2 3/5] avoid -Wuse-after-free [BZ #26779]

[Martin Sebor <msebor@gmail.com>]

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On 1/24/22 17:52, Martin Sebor wrote:
> This is a repost of the original patch but broken down by source
> file and with some suppression done by #pragma GCC diagnostic
> instead of conversion to intptr_t.  It also adds fixes for
> the same problem in the test suite that I overlooked before.

The attached patch suppresses the -Wuse-after-free instance in
io/ftw.c.

> 
> On 1/15/22 17:21, Martin Sebor wrote:
>> GCC 12 features a couple of new warnings designed to detect uses
>> of pointers made invalid by the pointees lifetimes having ended.
>> Building Glibc with the enhanced GCC exposes a few such uses,
>> mostly after successful calls to realloc.  The attached patch
>> avoids the new warnings by converting the pointers to uintptr_t
>> first and using the converted integers instead.
>>
>> The patch suppresses all instances of the warning at the strictest
>> setting (-Wuse-after-free=3), which includes even uses in equality
>> expressions.  The default setting approved for GCC 12 is
>> -Wuse-after-free=2, which doesn't warn on such uses to accommodate
>> the pointer-adjustment-after-realloc idiom.  At the default setting,
>> the changes to ldconfig.c and setenv are not necessary.
>>
>> Martin
> 

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diff --git a/io/ftw.c b/io/ftw.c
index 2742541f36..08ccbdd523 100644
--- a/io/ftw.c
+++ b/io/ftw.c
@@ -323,8 +323,8 @@ open_dir_stream (int *dfdp, struct ftw_data *data, struct dir_data *dirp)
 	  buf[actsize++] = '\0';
 
 	  /* Shrink the buffer to what we actually need.  */
-	  data->dirstreams[data->actdir]->content = realloc (buf, actsize);
-	  if (data->dirstreams[data->actdir]->content == NULL)
+	  void *content = realloc (buf, actsize);
+	  if (content == NULL)
 	    {
 	      int save_err = errno;
 	      free (buf);
@@ -338,6 +338,7 @@ open_dir_stream (int *dfdp, struct ftw_data *data, struct dir_data *dirp)
 	      data->dirstreams[data->actdir]->streamfd = -1;
 	      data->dirstreams[data->actdir] = NULL;
 	    }
+	  data->dirstreams[data->actdir]->content = content;
 	}
     }