From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Wed, 27 Apr 2016 14:51:01 +0000 (-0300)
Subject: libio: Fix fmemopen append mode failure (BZ# 20012)
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=52affab7cc2787033713b73bbc2a9c412469012f;p=thirdparty%2Fglibc.git

libio: Fix fmemopen append mode failure (BZ# 20012)

The fmemopen implementation does not account the file position correctly in
append mode. The following example shows the failure:

===
int main ()
{
  char buf[10] = "test";
  FILE *fp = fmemopen (buf, 10, "a+");
  fseek (fp, 0, SEEK_SET);

  int gr;
  if ((gr = getc (fp)) != 't' ||
      (gr = getc (fp)) != 'e' ||
      (gr = getc (fp)) != 's' ||
      (gr = getc (fp)) != 't' ||
      (gr = getc (fp)) != EOF)
    {
      printf ("%s: getc failed returned %i\n", __FUNCTION__, gr);
      return 1;
    }

  return 0;
}
===

This is due both how read and write operation update the buffer position,
taking in consideration buffer lenght instead of maximum position defined
by the open mode.  This patch fixes it and also fixes fseek not returning
EINVAL for invalid whence modes.

Tested on x86_64 and i686.

This is a backport of b65b205fbcabbb02463e31df17f5cabf7556f892.

	[BZ #20012]
	* libio/fmemopen.c (fmemopen_read): Use buffer maximum position, not
	length to calculate the buffer to read.
	(fmemopen_write): Set the buffer position based on bytes written.
	(fmemopen_seek): Return EINVAL for invalid whence modes.

(cherry picked from commit 321e1cef26ccbece949b16622ef74c203bd8ecc6)
---

diff --git a/libio/fmemopen.c b/libio/fmemopen.c
index 9264b724ee6..0f655909e8f 100644
--- a/libio/fmemopen.c
+++ b/libio/fmemopen.c
@@ -50,16 +50,14 @@ fmemopen_read (void *cookie, char *b, size_t s)
 
   if (c->pos + s > c->maxpos)
     {
-      if ((size_t) c->pos == c->maxpos)
-	return 0;
-      s = c->size - c->pos;
+      s = c->maxpos - c->pos;
+      if ((size_t) c->pos > c->maxpos)
+	s = 0;
     }
 
   memcpy (b, &(c->buffer[c->pos]), s);
 
   c->pos += s;
-  if ((size_t) c->pos > c->maxpos)
-    c->maxpos = c->pos;
 
   return s;
 }
@@ -70,28 +68,29 @@ fmemopen_write (void *cookie, const char *b, size_t s)
 {
   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;;
   _IO_off64_t pos = c->append ? c->maxpos : c->pos;
-  int addnullc;
-
-  addnullc = (s == 0 || b[s - 1] != '\0');
+  int addnullc = (s == 0 || b[s - 1] != '\0');
 
-  if (pos + s + addnullc > c->size)
+  if (pos + s > c->size)
     {
       if ((size_t) (c->pos + addnullc) >= c->size)
 	{
 	  __set_errno (ENOSPC);
 	  return 0;
 	}
-      s = c->size - pos - addnullc;
+      s = c->size - pos;
     }
 
   memcpy (&(c->buffer[pos]), b, s);
 
-  c->pos += s;
+  c->pos = pos + s;
   if ((size_t) c->pos > c->maxpos)
     {
       c->maxpos = c->pos;
-      if (addnullc)
+      if (c->maxpos < c->size && addnullc)
 	c->buffer[c->maxpos] = '\0';
+      /* A null byte is written in a stream open for update iff it fits.  */
+      else if (c->append == 0 && addnullc != 0)
+	c->buffer[c->size-1] = '\0';
     }
 
   return s;
@@ -123,7 +122,10 @@ fmemopen_seek (void *cookie, _IO_off64_t *p, int w)
     }
 
   if (np < 0 || (size_t) np > c->size)
-    return -1;
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
 
   *p = c->pos = np;
 
diff --git a/stdio-common/tst-fmemopen3.c b/stdio-common/tst-fmemopen3.c
index 250f9ecc75f..054b0697b3f 100644
--- a/stdio-common/tst-fmemopen3.c
+++ b/stdio-common/tst-fmemopen3.c
@@ -25,8 +25,13 @@ static void
 print_buffer (const char *s, size_t n)
 {
   size_t i;
+  printf ("{");
   for (i=0; i<n; ++i)
-    printf ("0x%02X (%c), ", s[i], s[i]);
+    {
+      printf ("0x%02X (%c)", s[i], s[i]);
+      if (i != n)
+	printf (", ");
+    }
 }
 
 /* This test check append mode initial position (a/a+) based on POSIX defition
@@ -185,6 +190,112 @@ do_test_read_seek_negative (void)
   return ret;
 }
 
+static int
+do_test_write_append_2 (const char *str)
+{
+  char buf[10];
+  size_t strn = strlen (str);
+  strcpy (buf, str);
+
+  FILE *fp = fmemopen (buf, sizeof (buf), "a+");
+  size_t r = ftell (fp);
+  size_t e = strlen (buf);
+  if (r != e)
+    {
+      printf ("%s: ftell returned %zu, expected %zu\n", __FUNCTION__, r, e);
+      return 1;
+    }
+
+  if (fseek (fp, 0, SEEK_SET) == -1)
+    {
+      printf ("%s: fseek returned -1\n", __FUNCTION__);
+      return 1;
+    }
+
+  int gr;
+  for (int i=0; i<strn; ++i)
+    {
+      if ((gr = getc (fp)) != str[i])
+	{
+	  printf ("%s: getc failed returned %d, expected %d\n", __FUNCTION__,
+		  gr, str[i]);
+	  return 1;
+        }
+    }
+  if ((gr = getc (fp)) != EOF)
+    {
+      printf ("%s: getc failed returned %d, expected EOF\n", __FUNCTION__,
+	      gr);
+      return 1;
+    }
+
+  if (fseek (fp, e+1, SEEK_SET) == -1)
+    {
+      printf ("%s: fseek returned -1\n", __FUNCTION__);
+      return 1;
+    }
+
+  if ((r = ftell (fp)) != e+1)
+    {
+      printf ("%s: ftell returned %zu, expected %zu\n", __FUNCTION__, r, e+1);
+      return 1;
+    }
+
+  if ((gr = getc (fp)) != EOF)
+    {
+      printf ("%s: getc failed returned %i\n", __FUNCTION__, gr);
+      return 1;
+    }
+
+  /* Check if internal position is not changed with a getc returning EOF.  */
+  if ((r = ftell (fp)) != e+1)
+    {
+      printf ("%s: ftell returned %zu, expected %zu\n", __FUNCTION__, r, e+1);
+      return 1;
+    }
+
+  if (fseek (fp, 0, SEEK_CUR) == -1)
+    {
+      printf ("%s: fseek returned -1\n", __FUNCTION__);
+      return 1;
+    }
+
+  /* This should be overwritten by fprintf + fflush.  */
+  buf[e+2] = 'X';
+
+  if ((r = fprintf (fp, "%d", 101)) != 3)
+    {
+      printf ("%s: fprintf returned %zu, expected %d\n", __FUNCTION__, r, 3);
+      return 1;
+    }
+
+  fflush (fp);
+
+  /* Check if internal position is changed by 3 (strlen of '101').  */
+  if ((r = ftell (fp)) != e+3)
+    {
+      printf ("%s: ftell returned %zu, expected %zu\n", __FUNCTION__, r, e+3);
+      return 1;
+    }
+
+  char exp[20];
+  sprintf (exp, "%s%d", str,  101);
+  if (memcmp (buf, exp, strlen (exp)) != 0)
+    {
+      printf ("%s: check failed:", __FUNCTION__);
+      printf ("\nexpected: ");
+      print_buffer (buf, sizeof (buf));
+      printf ("\nbuffer:   ");
+      print_buffer (exp, sizeof (exp));
+      printf ("\n");
+      return 1;
+    }
+
+  fclose(fp);
+
+  return 0;
+}
+
 static int
 do_test (void)
 {
@@ -199,6 +310,11 @@ do_test (void)
 
   ret += do_test_read_seek_negative ();
 
+  /* First test plus addend will fit in the define buffer of size 10.  */
+  ret += do_test_write_append_2 ("test");
+  /* The second test will also fit, but not the final '\0'.  */
+  ret += do_test_write_append_2 ("testing");
+
   return ret;
 }