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

diff --git a/ChangeLog b/ChangeLog
index 1e9511ec3a8b4fbf16d11fb425e56abfe1ec87ed..7d203366c95f2677c6d8cbd887ffb0c0f3cf1ad1 100644 (file)
--- 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.
+
 2014-11-19  Carlos O'Donell  <carlos@redhat.com>
            Florian Weimer  <fweimer@redhat.com>
            Joseph Myers  <joseph@codesourcery.com>

diff --git a/NEWS b/NEWS
index 8048bdb0b48a2c25a992a3b67a458835ba2e7b35..5dba8c893eb8f8c63b1cff1f54b5d15f5d6ec07f 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -9,8 +9,9 @@ Version 2.19.1
 
 * The following bugs are resolved with this release:
 
-  16545, 16617, 16683, 16689, 16701, 16706, 16707, 16739, 16815, 16619,
-  16740, 17031, 17048, 17137, 17153, 17187, 17213, 17325, 17625, 17630.
+  16545, 16617, 16618, 16683, 16689, 16701, 16706, 16707, 16739, 16815,
+  16619, 16740, 17031, 17048, 17137, 17153, 17187, 17213, 17325, 17625,
+  17630.
 
 * 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 1214c7d068356cddbd80dd2724720f06e8f8bc00..c62bee6a688bba9371a1f801fd3ad26f5863c01d 100644 (file)
--- a/stdio-common/tst-sscanf.c
+++ b/stdio-common/tst-sscanf.c
@@ -232,5 +232,38 @@ 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 2e1e91af78b509f903bce8f4bc95df48425aebfe..d7a18e3ab34d67e63875126ec284dbc7a951e2b1 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 (__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);                                   \