[PATCH v2] vfprintf-internal: Get rid of alloca.

[PATCH v2] vfprintf-internal: Get rid of alloca.

[Joe Simmons-Talbott]

Avoid potential stack overflow from unbounded alloca.  Use the existing
scratch_buffer instead.
---
Changes to v1:
* fix 32bit builds.
* ensure we have enough space in the scratch buffer before using it.

 stdio-common/vfprintf-internal.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/stdio-common/vfprintf-internal.c b/stdio-common/vfprintf-internal.c
index c76c06e49b..c05fc149d1 100644
--- a/stdio-common/vfprintf-internal.c
+++ b/stdio-common/vfprintf-internal.c
@@ -1066,6 +1066,8 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
   union printf_arg *args_value;
   int *args_size;
   int *args_type;
+  int *args_pa_user;
+  size_t args_pa_user_offset;
   {
     /* Calculate total size needed to represent a single argument
        across all three argument-related arrays.  */
@@ -1082,6 +1084,7 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
        now.  */
     args_size = &args_value[nargs].pa_int;
     args_type = &args_size[nargs];
+    args_pa_user = &args_type[nargs];
     memset (args_type, (mode_flags & PRINTF_FORTIFY) != 0 ? '\xff' : '\0',
 	    nargs * sizeof (*args_type));
   }
@@ -1171,7 +1174,25 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format,
 	else if (__glibc_unlikely (__printf_va_arg_table != NULL)
 		 && __printf_va_arg_table[args_type[cnt] - PA_LAST] != NULL)
 	  {
-	    args_value[cnt].pa_user = alloca (args_size[cnt]);
+	    if (args_pa_user + args_size[cnt] >
+	        (int *) &argsbuf + argsbuf.length)
+	      {
+		args_pa_user_offset = args_pa_user - &args_type[nargs];
+	        if (!scratch_buffer_grow_preserve (&argsbuf))
+	          {
+	            Xprintf_buffer_mark_failed (buf);
+	            goto all_done;
+	          }
+                args_value = argsbuf.data;
+                /* Set up the remaining two arrays to each point past the end of
+                   the prior array, since space for all three has been allocated
+                   now.  */
+                args_size = &args_value[nargs].pa_int;
+                args_type = &args_size[nargs];
+                args_pa_user = &args_type[nargs] + args_pa_user_offset;
+	      }
+	    args_value[cnt].pa_user = args_pa_user;
+	    args_pa_user += args_size[cnt];
 	    (*__printf_va_arg_table[args_type[cnt] - PA_LAST])
 	      (args_value[cnt].pa_user, ap_savep);
 	  }
-- 
2.39.2