Re: [PATCH v2 5/5] 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
the testsuite.

> 
> 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/malloc/tst-malloc-backtrace.c b/malloc/tst-malloc-backtrace.c
index ea66da23ef..8a3f4a0b55 100644
--- a/malloc/tst-malloc-backtrace.c
+++ b/malloc/tst-malloc-backtrace.c
@@ -20,6 +20,7 @@
 #include <stdlib.h>
 
 #include <support/support.h>
+#include <libc-diag.h>
 
 #define SIZE 4096
 
@@ -29,7 +30,15 @@ __attribute__((noinline))
 call_free (void *ptr)
 {
   free (ptr);
+#if __GNUC_PREREQ (12, 0)
+  /* Ignore a valid warning about using a pointer made indeterminate
+     by a prior call to malloc().  */
+  DIAG_IGNORE_NEEDS_COMMENT (12, "-Wuse-after-free");
+#endif
   *(size_t *)(ptr - sizeof (size_t)) = 1;
+#if __GNUC_PREREQ (12, 0)
+  DIAG_POP_NEEDS_COMMENT;
+#endif
 }
 
 int
diff --git a/malloc/tst-malloc-check.c b/malloc/tst-malloc-check.c
index 46938c0dbb..eb46cf3bbb 100644
--- a/malloc/tst-malloc-check.c
+++ b/malloc/tst-malloc-check.c
@@ -86,7 +86,15 @@ do_test (void)
     merror ("errno is not set correctly.");
   DIAG_POP_NEEDS_COMMENT;
 
+#if __GNUC_PREREQ (12, 0)
+  /* Ignore a valid warning about using a pointer made indeterminate
+     by a prior call to realloc().  */
+  DIAG_IGNORE_NEEDS_COMMENT (12, "-Wuse-after-free");
+#endif
   free (p);
+#if __GNUC_PREREQ (12, 0)
+  DIAG_POP_NEEDS_COMMENT;
+#endif
 
   p = malloc (512);
   if (p == NULL)
@@ -104,7 +112,15 @@ do_test (void)
     merror ("errno is not set correctly.");
   DIAG_POP_NEEDS_COMMENT;
 
+#if __GNUC_PREREQ (12, 0)
+  /* Ignore a valid warning about using a pointer made indeterminate
+     by a prior call to realloc().  */
+  DIAG_IGNORE_NEEDS_COMMENT (12, "-Wuse-after-free");
+#endif
   free (p);
+#if __GNUC_PREREQ (12, 0)
+  DIAG_POP_NEEDS_COMMENT;
+#endif
   free (q);
 
   return errors != 0;
diff --git a/malloc/tst-malloc-too-large.c b/malloc/tst-malloc-too-large.c
index e23aa08e4f..dac3c8086c 100644
--- a/malloc/tst-malloc-too-large.c
+++ b/malloc/tst-malloc-too-large.c
@@ -95,7 +95,15 @@ test_large_allocations (size_t size)
   DIAG_POP_NEEDS_COMMENT;
 #endif
   TEST_VERIFY (errno == ENOMEM);
+#if __GNUC_PREREQ (12, 0)
+  /* Ignore a warning about using a pointer made indeterminate by
+     a prior call to realloc().  */
+  DIAG_IGNORE_NEEDS_COMMENT (12, "-Wuse-after-free");
+#endif
   free (ptr_to_realloc);
+#if __GNUC_PREREQ (12, 0)
+  DIAG_POP_NEEDS_COMMENT;
+#endif
 
   for (size_t nmemb = 1; nmemb <= 8; nmemb *= 2)
     if ((size % nmemb) == 0)
@@ -113,14 +121,30 @@ test_large_allocations (size_t size)
         test_setup ();
         TEST_VERIFY (reallocarray (ptr_to_realloc, nmemb, size / nmemb) == NULL);
         TEST_VERIFY (errno == ENOMEM);
+#if __GNUC_PREREQ (12, 0)
+  /* Ignore a warning about using a pointer made indeterminate by
+     a prior call to realloc().  */
+  DIAG_IGNORE_NEEDS_COMMENT (12, "-Wuse-after-free");
+#endif
         free (ptr_to_realloc);
+#if __GNUC_PREREQ (12, 0)
+  DIAG_POP_NEEDS_COMMENT;
+#endif
 
         ptr_to_realloc = malloc (16);
         TEST_VERIFY_EXIT (ptr_to_realloc != NULL);
         test_setup ();
         TEST_VERIFY (reallocarray (ptr_to_realloc, size / nmemb, nmemb) == NULL);
         TEST_VERIFY (errno == ENOMEM);
+#if __GNUC_PREREQ (12, 0)
+  /* Ignore a warning about using a pointer made indeterminate by
+     a prior call to realloc().  */
+  DIAG_IGNORE_NEEDS_COMMENT (12, "-Wuse-after-free");
+#endif
         free (ptr_to_realloc);
+#if __GNUC_PREREQ (12, 0)
+  DIAG_POP_NEEDS_COMMENT;
+#endif
       }
     else
       break;
diff --git a/support/tst-support-open-dev-null-range.c b/support/tst-support-open-dev-null-range.c
index 3ed3177d57..e7526597ce 100644
--- a/support/tst-support-open-dev-null-range.c
+++ b/support/tst-support-open-dev-null-range.c
@@ -26,6 +26,8 @@
 #include <sys/resource.h>
 #include <stdlib.h>
 
+#include <libc-diag.h>
+
 #ifndef PATH_MAX
 # define PATH_MAX 1024
 #endif
@@ -41,8 +43,18 @@ check_path (int fd)
     = readlink (proc_fd_path, file_path, sizeof (file_path));
   free (proc_fd_path);
   if (file_path_length < 0)
-    FAIL_EXIT1 ("readlink (%s, %p, %zu)", proc_fd_path, file_path,
-		sizeof (file_path));
+    {
+#if __GNUC_PREREQ (12, 0)
+  /* Ignore a valid warning about using a pointer made indeterminate
+     by a prior call to free().  */
+  DIAG_IGNORE_NEEDS_COMMENT (12, "-Wuse-after-free");
+#endif
+      FAIL_EXIT1 ("readlink (%s, %p, %zu)", proc_fd_path, file_path,
+		  sizeof (file_path));
+#if __GNUC_PREREQ (12, 0)
+      DIAG_POP_NEEDS_COMMENT;
+#endif
+    }
   file_path[file_path_length] = '\0';
   TEST_COMPARE_STRING (file_path, "/dev/null");
 }