Subject: ASAN failures in dir.c

From: Gisle Vanem <[email-masked]>
Date: Tue, 27 Jun 2023 15:04:48 +0200

Hello list.

Since some time ago, building diff.exe with ASAN (on Windows-10),
causes it to trigger on illegal use of memcpy().
For example:

==3752==ERROR: AddressSanitizer: heap-use-after-free on address 0x121647e20772 at
pc 0x7ffc6e93727e bp 0x00d589efdba0 sp 0x00d589efd330
WRITE of size 17 at 0x121647e20772 thread T0
     #0 0x7ffc6e93727d in __asan_memcpy 
D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\li\asan\asan_interceptors_memintrinsics.cpp:22
     #1 0x7ff604834af1 in dir_read F:\MinGW32\src\gnu\GNU-diff\src\dir.c:101
     #2 0x7ff604832ec7 in diff_dirs F:\MinGW32\src\gnu\GNU-diff\src\dir.c:214
     #3 0x7ff60482dc37 in compare_files F:\MinGW32\src\gnu\GNU-diff\src\diff.c:1369
     #4 0x7ff604833b1b in diff_dirs F:\MinGW32\src\gnu\GNU-diff\src\dir.c:289
     #5 0x7ff60482dc37 in compare_files F:\MinGW32\src\gnu\GNU-diff\src\diff.c:1369
     #6 0x7ff60483270e in main F:\MinGW32\src\gnu\GNU-diff\src\diff.c:862
     ...

-----------------------

This causes Heap Corruption all over the place.

I'm not sure this is an issue with Gnulib or diff. But reverting this
patch:

diff --git a/src/dir.c b/src/dir.c
index ba9403b..773afeb 100644
--- a/src/dir.c
+++ b/src/dir.c
@@ -95,13 +95,9 @@ dir_read (struct file_data const *dir, struct dirdata *dirdata)
            if (excluded_file_name (excluded, d_name))
              continue;

-          while (data_alloc - data_used < d_size)
-            {
-              if (IDX_MAX / 2 <= data_alloc)
-                xalloc_die ();
-              dirdata->data = data = xirealloc (data, data_alloc *= 2);
-            }
-
+          if (data_alloc - data_used < d_size)
+	    dirdata->data = xpalloc (dirdata->data, &data_alloc,
+				     d_size - (data_alloc - data_used), -1, 1);
            memcpy (data + data_used, d_name, d_size);
            data_used += d_size;
            nnames++;

--------

it work with ASAN too (although much slower).

-- 
--gv