CVE-2015-1472: wscanf allocates too little memory

BZ #16618

Under certain conditions wscanf can allocate too little memory for the
to-be-scanned arguments and overflow the allocated buffer.  The
implementation now correctly computes the required buffer size when
using malloc.

A regression test was added to tst-sscanf.

Conflicts:
	ChangeLog
	NEWS

4 files changed, 49 insertions, 7 deletions

diff --git a/ChangeLog b/ChangeLog
index ad9df0f243..b0b9debca0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2015-02-05  Paul Pluzhnikov  <ppluzhnikov@google.com>
+
+	[BZ #16618]
+	* stdio-common/tst-sscanf.c (main): Test for buffer overflow.
+	* stdio-common/vfscanf.c (_IO_vfscanf_internal): Compute needed
+	size in bytes. Store needed elements in wpmax. Use needed size
+	in bytes for extend_alloca.
+
 2014-05-26  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
 
 	* sysdeps/powerpc/powerpc32/power4/memset.S (memset): Replace insrdi
diff --git a/NEWS b/NEWS
index 1c9acf3708..754ac0a7e4 100644
--- a/NEWS
+++ b/NEWS
@@ -11,7 +11,8 @@ Version 2.18.1
 
   14143, 14155, 14547, 14699, 15532, 15427, 15522, 15680, 15723, 15734,
   15735, 15797, 15892, 15895, 15909, 15915, 15917, 15996, 16072, 16150,
-  16414, 16430, 16431, 16617, 17048, 17137, 17187, 17325, 17625, 17630.
+  16414, 16430, 16431, 16617, 16618, 17048, 17137, 17187, 17325, 17625,
+  17630.
 
 * Support for powerpc64le has been added.
 
diff --git a/stdio-common/tst-sscanf.c b/stdio-common/tst-sscanf.c
index 3c34f58a63..8f73c9510b 100644
--- a/stdio-common/tst-sscanf.c
+++ b/stdio-common/tst-sscanf.c
@@ -230,5 +230,38 @@ main (void)
 	}
     }
 
+  /* BZ #16618
+     The test will segfault during SSCANF if the buffer overflow
+     is not fixed.  The size of `s` is such that it forces the use
+     of malloc internally and this triggers the incorrect computation.
+     Thus the value for SIZE is arbitrariy high enough that malloc
+     is used.  */
+  {
+#define SIZE 131072
+    CHAR *s = malloc ((SIZE + 1) * sizeof (*s));
+    if (s == NULL)
+      abort ();
+    for (size_t i = 0; i < SIZE; i++)
+      s[i] = L('0');
+    s[SIZE] = L('\0');
+    int i = 42;
+    /* Scan multi-digit zero into `i`.  */
+    if (SSCANF (s, L("%d"), &i) != 1)
+      {
+	printf ("FAIL: bug16618: SSCANF did not read one input item.\n");
+	result = 1;
+      }
+    if (i != 0)
+      {
+	printf ("FAIL: bug16618: Value of `i` was not zero as expected.\n");
+	result = 1;
+      }
+    free (s);
+    if (result != 1)
+      printf ("PASS: bug16618: Did not crash.\n");
+#undef SIZE
+  }
+
+
   return result;
 }
diff --git a/stdio-common/vfscanf.c b/stdio-common/vfscanf.c
index 093c8b0c58..8980a6ec8d 100644
--- a/stdio-common/vfscanf.c
+++ b/stdio-common/vfscanf.c
@@ -272,9 +272,10 @@ _IO_vfscanf_internal (_IO_FILE *s, const char *format, _IO_va_list argptr,
       if (__builtin_expect (wpsize == wpmax, 0))			    \
 	{								    \
 	  CHAR_T *old = wp;						    \
-	  size_t newsize = (UCHAR_MAX + 1 > 2 * wpmax			    \
-			    ? UCHAR_MAX + 1 : 2 * wpmax);		    \
-	  if (use_malloc || !__libc_use_alloca (newsize))		    \
+	  bool fits = __glibc_likely (wpmax <= SIZE_MAX / sizeof (CHAR_T) / 2); \
+	  size_t wpneed = MAX (UCHAR_MAX + 1, 2 * wpmax);		    \
+	  size_t newsize = fits ? wpneed * sizeof (CHAR_T) : SIZE_MAX;	    \
+	  if (!__libc_use_alloca (newsize))				    \
 	    {								    \
 	      wp = realloc (use_malloc ? wp : NULL, newsize);		    \
 	      if (wp == NULL)						    \
@@ -286,14 +287,13 @@ _IO_vfscanf_internal (_IO_FILE *s, const char *format, _IO_va_list argptr,
 		}							    \
 	      if (! use_malloc)						    \
 		MEMCPY (wp, old, wpsize);				    \
-	      wpmax = newsize;						    \
+	      wpmax = wpneed;						    \
 	      use_malloc = true;					    \
 	    }								    \
 	  else								    \
 	    {								    \
 	      size_t s = wpmax * sizeof (CHAR_T);			    \
-	      wp = (CHAR_T *) extend_alloca (wp, s,			    \
-					     newsize * sizeof (CHAR_T));    \
+	      wp = (CHAR_T *) extend_alloca (wp, s, newsize);		    \
 	      wpmax = s / sizeof (CHAR_T);				    \
 	      if (old != NULL)						    \
 		MEMCPY (wp, old, wpsize);				    \