elf: Fix alloca size in _dl_debug_vdprintf

The alloca size did not consider the optional width parameter for
padding which could cause buffer underflow. The width is currently used
e.g. by _dl_map_object_from_fd which passes 2 * sizeof(void *) which
can be larger than the alloca buffer size on targets where
sizeof(void *) >= 2 * sizeof(unsigned long).

Even if large width is not used on existing targets it is better to fix
the formatting code to avoid surprises.

diff --git a/elf/dl-printf.c b/elf/dl-printf.c
index d3264ba96cd959bf3571791d83e3a8ebb73c3f58..10efa925bdfb48bc417ebefb02f199d5113e54c4 100644 (file)
--- a/elf/dl-printf.c
+++ b/elf/dl-printf.c
@@ -163,8 +163,11 @@ _dl_debug_vdprintf (int fd, int tag_p, const char *fmt, va_list arg)
                /* We use alloca() to allocate the buffer with the most
                   pessimistic guess for the size.  Using alloca() allows
                   having more than one integer formatting in a call.  */
-               char *buf = (char *) alloca (1 + 3 * sizeof (unsigned long int));
-               char *endp = &buf[1 + 3 * sizeof (unsigned long int)];
+               int size = 1 + 3 * sizeof (unsigned long int);
+               if (width + 1 > size)
+                 size = width + 1;
+               char *buf = (char *) alloca (size);
+               char *endp = &buf[size];
                char *cp = _itoa (num, endp, *fmt == 'x' ? 16 : 10, 0);
 
                /* Pad to the width the user specified.  */