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authorPaul Pluzhnikov <ppluzhnikov@google.com>2015-02-06 00:30:42 -0500
committerCarlos O'Donell <carlos@systemhalted.org>2015-02-06 00:34:51 -0500
commit5bd80bfe9ca0d955bfbbc002781bc7b01b6bcb06 (patch)
treea77a8efbf88a4eed15cfefe4e5d570d380985c1c /stdio-common
parent04cb913ddf67ac90da274dd32b6ceafd57ca36ca (diff)
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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.
Diffstat (limited to 'stdio-common')
-rw-r--r--stdio-common/tst-sscanf.c33
-rw-r--r--stdio-common/vfscanf.c12
2 files changed, 39 insertions, 6 deletions
diff --git a/stdio-common/tst-sscanf.c b/stdio-common/tst-sscanf.c
index aece3f2f29..8a2eb9e39c 100644
--- a/stdio-common/tst-sscanf.c
+++ b/stdio-common/tst-sscanf.c
@@ -233,5 +233,38 @@ 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 cd129a81de..0e204e7b32 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 (__glibc_unlikely (wpsize == wpmax))				      \
 	{								    \
 	  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);				    \