@@ -230,6 +230,7 @@ tests := \
tst-fseek \
tst-fwrite \
tst-fwrite-memstrm \
+ tst-fwrite-overflow \
tst-fwrite-ro \
tst-getline \
tst-getline-enomem \
new file mode 100644
@@ -0,0 +1,130 @@
+/* Test the overflow of fwrite's internal buffer.
+ Copyright (C) 2024 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+/* stdio.h provides BUFSIZ, which is the size of fwrite's internal buffer. */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/support.h>
+#include <support/xstdio.h>
+#include <support/xunistd.h>
+
+/* Length of the buffers in bytes. */
+#define RWBUF_SIZE (2 * BUFSIZ)
+
+void
+test_one_rw (const char *in, size_t size, size_t nmemb, size_t blocks)
+{
+ int fd;
+ FILE *f;
+ char *out;
+ size_t written, to_write;
+ const size_t requested = size * nmemb;
+
+ printf ("Testing with size = %zd, nmemb = %zd, blocks = %zd\n",
+ size, nmemb, blocks);
+
+ TEST_VERIFY_EXIT (requested <= RWBUF_SIZE);
+ /* Ensure fwrite's internal buffer will overflow. */
+ TEST_VERIFY_EXIT (requested > BUFSIZ);
+
+ /* Create a temporary file and open it for reading and writing. */
+ fd = create_temp_file ("tst-fwrite-overflow", NULL);
+ TEST_VERIFY_EXIT (fd != -1);
+ f = fdopen (fd, "w+");
+ TEST_VERIFY_EXIT (f != NULL);
+
+ /* Call fwrite() as many times as needed, until all data is written,
+ limiting the amount of data written per call to block items. */
+ for (written = 0; written < nmemb; written += to_write)
+ {
+ if (written + blocks <= nmemb)
+ to_write = blocks;
+ else
+ to_write = nmemb - written;
+ /* Check if fwrite() returns the expected value. No errors are
+ expected. */
+ TEST_COMPARE (fwrite (in + size * written, size, to_write, f),
+ to_write);
+ TEST_COMPARE (ferror (f), 0);
+ }
+ TEST_VERIFY_EXIT (written == nmemb);
+
+ /* Ensure all the data is flushed to file. */
+ TEST_COMPARE (fflush (f), 0);
+
+ /* We have to check if the contents in the file are correct. Go back to
+ the beginning of the file. */
+ rewind (f);
+ /* Try to allocate a buffer and save the contents of the generated file to
+ it. */
+ out = xmalloc (RWBUF_SIZE);
+ TEST_COMPARE (fread (out, size, nmemb, f), nmemb);
+
+ /* Ensure the output has the expected contents. */
+ TEST_COMPARE (memcmp (out, in, requested), 0);
+
+ xfclose (f);
+ free (out);
+}
+
+static int
+do_test (void)
+{
+ char * in;
+ int i, j;
+ size_t nmemb[] = {BUFSIZ + 1, RWBUF_SIZE, 0};
+ /* Maximum number of items written for each fwrite call. */
+ size_t block[] = {100, 1024, 2047, 0};
+ /* The largest block must fit entirely in fwrite's buffer. */
+ _Static_assert (2047 < BUFSIZ,
+ "a block must fit in fwrite's internal buffer");
+
+ in = xmalloc (RWBUF_SIZE);
+ for (i = 0; i < RWBUF_SIZE; i++)
+ in[i] = i % 0xff;
+
+ for (i = 0; nmemb[i] != 0; i++)
+ for (j = 0; block[j] != 0; j++)
+ {
+ /* Run a test with an array of nmemb bytes. Write at most block
+ items per fwrite call. */
+ test_one_rw (in, 1, nmemb[i], block[j]);
+ /* Run a test that overflows fwrite's internal buffer in a single call
+ by writting a single item of nmemb bytes.
+ This call should not use the buffer and should be written directly
+ to the file. */
+ test_one_rw (in, nmemb[i], 1, nmemb[i]);
+ }
+
+ for (j = 0; block[j] != 0; j++)
+ {
+ /* Run a test with size=2 and the minimum nmemb value that still
+ overflows the buffer. Write at most block items per fwrite call. */
+ test_one_rw (in, 2, BUFSIZ / 2 + 1, block[j]);
+ /* Likewise, but size=3. */
+ test_one_rw (in, 3, BUFSIZ / 3 + 1, block[j]);
+ }
+
+ free (in);
+ return 0;
+}
+
+#include <support/test-driver.c>