diff mbox series

[v4] vfprintf-internal: Get rid of alloca.

Message ID 20230614183826.3358014-1-josimmon@redhat.com
State New
Headers show
Series [v4] vfprintf-internal: Get rid of alloca. | expand

Commit Message

Joe Simmons-Talbott June 14, 2023, 6:38 p.m. UTC 
Avoid potential stack overflow from unbounded alloca.  Use the existing
scratch_buffer instead.

Add a testcase to exercise the code as suggested by Adhemerval Zanella Netto.
---
Changes to v3:
  * Add a testcase to exercise the code.
  * Fix arg_pa_user pointer math by using (void *) rather than (int *).

 stdio-common/tst-vfprintf-user-type.c | 43 +++++++++++++++++++++++++++
 stdio-common/vfprintf-internal.c      | 23 +++++++++++++-
 2 files changed, 65 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/stdio-common/tst-vfprintf-user-type.c b/stdio-common/tst-vfprintf-user-type.c
index 7cc69dc716..bd2ac04351 100644
--- a/stdio-common/tst-vfprintf-user-type.c
+++ b/stdio-common/tst-vfprintf-user-type.c
@@ -194,6 +194,49 @@  do_test (void)
   TEST_COMPARE_STRING (str, "[[(123, 457.000000) (123, 457.000000)]]");
   free (str);
 
+  str = NULL;
+  TEST_VERIFY (asprintf_alias (&str, "%1$P %2$P %3$P %4$P %5$P %6$P"
+                                    "%7$P %8$P %9$P %10$P %11$P %12$P"
+                                    "%13$P %14$P %15$P %16$P %17$P %18$P"
+                                    "%19$P %20$P %21$P %22$P %23$P %24$P"
+                                    "%25$P %26$P %27$P %28$P", /*%*29$P %30$P",*/
+                              1L, 1.0,
+                              2L, 2.0,
+                              3L, 3.0,
+                              4L, 4.0,
+                              5L, 6.0,
+                              6L, 6.0,
+                              7L, 7.0,
+                              8L, 8.0,
+                              9L, 9.0,
+                              10L, 10.0,
+                              11L, 11.0,
+                              12L, 12.0,
+                              13L, 13.0,
+                              14L, 14.0,
+                              15L, 15.0,
+                              16L, 16.0,
+                              17L, 17.0,
+                              18L, 18.0,
+                              19L, 19.0,
+                              20L, 20.0,
+                              21L, 21.0,
+                              22L, 22.0,
+                              23L, 23.0,
+                              24L, 34.0,
+                              25L, 25.0,
+                              26L, 26.0,
+                              27L, 27.0,
+                              28L, 28.0)
+              >= 0);
+  printf ("str=%s\n", str);
+  free (str);
+
+  str = NULL;
+  TEST_VERIFY (asprintf_alias (&str, "[[%1$P %1$P]]", 123L, 457.0) >= 0);
+  TEST_COMPARE_STRING (str, "[[(123, 457.000000) (123, 457.000000)]]");
+  free (str);
+
   str = NULL;
   TEST_VERIFY (asprintf_alias (&str, "[[%.1P]]", 1L, 2.0) >= 0);
   TEST_COMPARE_STRING (str, "[[{(1, 2.000000)}]]");
diff --git a/stdio-common/vfprintf-internal.c b/stdio-common/vfprintf-internal.c
index c76c06e49b..b18d70d993 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;
+  void *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]);
+	    while (args_pa_user + args_size[cnt] >
+		argsbuf.data + argsbuf.length)
+	      {
+		args_pa_user_offset = args_pa_user - (void *) &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 = (void *) &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);
 	  }