Fix fwrite() reading beyond end of buffer in error path

Partially revert commits 2b766585f9b4ffabeef2f36200c275976b93f2c7 and
de2fd463b1c0310d75084b6d774fb974075a4ad9, which were intended to fix BZ#11741
but caused another, likely worse bug, namely that fwrite() and fputs() could,
in an error path, read data beyond the end of the specified buffer, and
potentially even write this data to the file.

Fix BZ#11741 properly by checking the return value from _IO_padn() in
stdio-common/vfprintf.c.

8 files changed, 50 insertions, 36 deletions

diff --git a/ChangeLog b/ChangeLog
index 5d99bd810b..c4a5d8490a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,20 @@
+2013-10-11  Eric Biggers  <ebiggers3@gmail.com>
+
+	[BZ #15362]
+	* libio/fileops.c (_IO_new_file_write): Return count of bytes
+	written.
+	(_IO_new_file_xsputn): Don't return EOF if nothing has been
+	written.
+	* libio/iofwrite.c (_IO_fwrite): Return count if bytes were
+	written to buffer but not flushed.
+	* libio/iofwrite_u.c:  Likewise.
+	* libio/iopadn.c:  Return bytes returned even if EOF was
+	encountered.
+	* libio/iowpadn.c:  Likewise.
+	* stdio-common/vfprintf.c [COMPILE_WPRINTF] (PAD): Return error
+	if _IO_padn does not write the whole buffer.
+	[!COMPILE_WPRINTF] (PAD): Likewise.
+
 2013-10-10  David S. Miller  <davem@davemloft.net>
 
 	* sysdeps/posix/dirstream.h (struct __dirstream): Fix alignment of
diff --git a/NEWS b/NEWS
index 5f0a710503..48a92e8365 100644
--- a/NEWS
+++ b/NEWS
@@ -9,12 +9,12 @@ Version 2.19
 
 * The following bugs are resolved with this release:
 
-  156, 431, 13982, 13985, 14155, 14547, 14699, 15048, 15400, 15427, 15522,
-  15531, 15532, 15608, 15609, 15610, 15632, 15640, 15680, 15681, 15723,
-  15734, 15735, 15736, 15748, 15749, 15754, 15760, 15797, 15844, 15849,
-  15855, 15856, 15857, 15859, 15867, 15886, 15887, 15890, 15892, 15893,
-  15895, 15897, 15905, 15909, 15919, 15921, 15923, 15939, 15963, 15966,
-  15988, 16034.
+  156, 431, 13982, 13985, 14155, 14547, 14699, 15048, 15362, 15400, 15427,
+  15522, 15531, 15532, 15608, 15609, 15610, 15632, 15640, 15680, 15681,
+  15723, 15734, 15735, 15736, 15748, 15749, 15754, 15760, 15797, 15844,
+  15849, 15855, 15856, 15857, 15859, 15867, 15886, 15887, 15890, 15892,
+  15893, 15895, 15897, 15905, 15909, 15919, 15921, 15923, 15939, 15963,
+  15966, 15988, 16034.
 
 * CVE-2012-4412 The strcoll implementation caches indices and rules for
   large collation sequences to optimize multiple passes.  This cache
diff --git a/libio/fileops.c b/libio/fileops.c
index e92f85b243..c58e860c04 100644
--- a/libio/fileops.c
+++ b/libio/fileops.c
@@ -1245,13 +1245,12 @@ _IO_new_file_write (f, data, n)
      _IO_ssize_t n;
 {
   _IO_ssize_t to_do = n;
-  _IO_ssize_t count = 0;
   while (to_do > 0)
     {
-      count = (__builtin_expect (f->_flags2
-				 & _IO_FLAGS2_NOTCANCEL, 0)
-	       ? write_not_cancel (f->_fileno, data, to_do)
-	       : write (f->_fileno, data, to_do));
+      _IO_ssize_t count = (__builtin_expect (f->_flags2
+					     & _IO_FLAGS2_NOTCANCEL, 0)
+			   ? write_not_cancel (f->_fileno, data, to_do)
+			   : write (f->_fileno, data, to_do));
       if (count < 0)
 	{
 	  f->_flags |= _IO_ERR_SEEN;
@@ -1263,7 +1262,7 @@ _IO_new_file_write (f, data, n)
   n -= to_do;
   if (f->_offset >= 0)
     f->_offset += n;
-  return count < 0 ? count : n;
+  return n;
 }
 
 _IO_size_t
@@ -1323,13 +1322,11 @@ _IO_new_file_xsputn (f, data, n)
       _IO_size_t block_size, do_write;
       /* Next flush the (full) buffer. */
       if (_IO_OVERFLOW (f, EOF) == EOF)
-	/* If nothing else has to be written or nothing has been written, we
-	   must not signal the caller that the call was even partially
-	   successful.  */
-	return (to_do == 0 || to_do == n) ? EOF : n - to_do;
+	/* If nothing else has to be written we must not signal the
+	   caller that everything has been written.  */
+	return to_do == 0 ? EOF : n - to_do;
 
-      /* Try to maintain alignment: write a whole number of blocks.
-	 dont_write is what gets left over. */
+      /* Try to maintain alignment: write a whole number of blocks.  */
       block_size = f->_IO_buf_end - f->_IO_buf_base;
       do_write = to_do - (block_size >= 128 ? to_do % block_size : 0);
 
diff --git a/libio/iofwrite.c b/libio/iofwrite.c
index 81596a64c4..66542eaea5 100644
--- a/libio/iofwrite.c
+++ b/libio/iofwrite.c
@@ -42,12 +42,12 @@ _IO_fwrite (buf, size, count, fp)
   if (_IO_vtable_offset (fp) != 0 || _IO_fwide (fp, -1) == -1)
     written = _IO_sputn (fp, (const char *) buf, request);
   _IO_release_lock (fp);
-  /* We are guaranteed to have written all of the input, none of it, or
-     some of it.  */
-  if (written == request)
+  /* We have written all of the input in case the return value indicates
+     this or EOF is returned.  The latter is a special case where we
+     simply did not manage to flush the buffer.  But the data is in the
+     buffer and therefore written as far as fwrite is concerned.  */
+  if (written == request || written == EOF)
     return count;
-  else if (written == EOF)
-    return 0;
   else
     return written / size;
 }
diff --git a/libio/iofwrite_u.c b/libio/iofwrite_u.c
index 4a9d6caa04..18dc6d032d 100644
--- a/libio/iofwrite_u.c
+++ b/libio/iofwrite_u.c
@@ -44,12 +44,12 @@ fwrite_unlocked (buf, size, count, fp)
   if (_IO_fwide (fp, -1) == -1)
     {
       written = _IO_sputn (fp, (const char *) buf, request);
-      /* We are guaranteed to have written all of the input, none of it, or
-	 some of it.  */
-      if (written == request)
+      /* We have written all of the input in case the return value indicates
+	 this or EOF is returned.  The latter is a special case where we
+	 simply did not manage to flush the buffer.  But the data is in the
+	 buffer and therefore written as far as fwrite is concerned.  */
+      if (written == request || written == EOF)
 	return count;
-      else if (written == EOF)
-	return 0;
     }
 
   return written / size;
diff --git a/libio/iopadn.c b/libio/iopadn.c
index cc93c0f7ac..5ebbcf4551 100644
--- a/libio/iopadn.c
+++ b/libio/iopadn.c
@@ -59,7 +59,7 @@ _IO_padn (fp, pad, count)
       w = _IO_sputn (fp, padptr, PADSIZE);
       written += w;
       if (w != PADSIZE)
-	return w == EOF ? w : written;
+	return written;
     }
 
   if (i > 0)
diff --git a/libio/iowpadn.c b/libio/iowpadn.c
index d94db71f2b..5600f3711c 100644
--- a/libio/iowpadn.c
+++ b/libio/iowpadn.c
@@ -65,7 +65,7 @@ _IO_wpadn (fp, pad, count)
       w = _IO_sputn (fp, (char *) padptr, PADSIZE);
       written += w;
       if (w != PADSIZE)
-	return w == EOF ? w : written;
+	return written;
     }
 
   if (i > 0)
diff --git a/stdio-common/vfprintf.c b/stdio-common/vfprintf.c
index fb22f6969e..8cd7a85b21 100644
--- a/stdio-common/vfprintf.c
+++ b/stdio-common/vfprintf.c
@@ -90,13 +90,13 @@
   do {									      \
     if (width > 0)							      \
       {									      \
-	unsigned int d = _IO_padn (s, (Padchar), width);		      \
-	if (__glibc_unlikely (d == EOF))				      \
+	_IO_ssize_t written = _IO_padn (s, (Padchar), width);		      \
+	if (__glibc_unlikely (written != width))			      \
 	  {								      \
 	    done = -1;							      \
 	    goto all_done;						      \
 	  }								      \
-	done_add (d);							      \
+	done_add (written);						      \
       }									      \
   } while (0)
 # define PUTC(C, F)	_IO_putc_unlocked (C, F)
@@ -119,13 +119,13 @@
   do {									      \
     if (width > 0)							      \
       {									      \
-	unsigned int d = _IO_wpadn (s, (Padchar), width);		      \
-	if (__glibc_unlikely (d == EOF))				      \
+	_IO_ssize_t written = _IO_wpadn (s, (Padchar), width);		      \
+	if (__glibc_unlikely (written != width))			      \
 	  {								      \
 	    done = -1;							      \
 	    goto all_done;						      \
 	  }								      \
-	done_add (d);							      \
+	done_add (written);						      \
       }									      \
   } while (0)
 # define PUTC(C, F)	_IO_putwc_unlocked (C, F)