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.

(cherry picked from commit 5bd80bfe9ca0d955bfbbc002781bc7b01b6bcb06)

Conflicts:
	ChangeLog
	NEWS

diff --git a/ChangeLog b/ChangeLog
index a6461e6821e08fec43c54ed08c11173c65c1e58c..ccce486c9d6499bcc5403a8938fe36d855e1ec8d 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2015-02-16  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.
+
 2015-02-16  H.J. Lu  <hongjiu.lu@intel.com>
 
        [BZ #17801]

diff --git a/NEWS b/NEWS
index 0eb3fb3e7f08af8daf922a91882b52b974dd9182..976f2ea0236ffa3e26c0b6ca1b5fb4810caf3818 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -9,8 +9,13 @@ Version 2.20.1
 
 * The following bugs are resolved with this release:
 
-  16009, 16617, 17266, 17370, 17371, 17460, 17485, 17555, 17625, 17630,
-  17801.
+  16009, 16617, 16618, 17266, 17370, 17371, 17460, 17485, 17555, 17625,
+  17630, 17801.
+
+* CVE-2015-1472 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.
 
 * CVE-2104-7817 The wordexp function could ignore the WRDE_NOCMD flag
   under certain input conditions resulting in the execution of a shell for

diff --git a/stdio-common/tst-sscanf.c b/stdio-common/tst-sscanf.c
index 9fef93a5357813acb873b53bd9e4398b7aadd996..6394fe1cccd1c6e2a3a81a577a446c57da9fee09 100644 (file)
--- 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 e0d224530cc67498c3fa5b37838d5bdcdf08eb28..a4f06b44e576e22a4a28c5badee9a8d757014d21 100644 (file)
--- 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);                                   \