[PATCH] Fix vfwscanf(3) assignment suppression flag handling bug

Lucio Andrés Illanes Albornoz lucio@lucioillanes.de
Sat Jun 1 08:33:00 GMT 2019

newlib's vfwscanf(3) (or specifically, __SVFWSCANF_R()) fails to correctly set
the assignment-suppressing character (`*') flag[1] which, when present in the
formatting string, results in undefined behaviour comprising retrieving and
dereferencing a pointer that was not supplied by the caller as such or at all.
When compared to the vfscanf(3) implementation, this would appear to be over
the missing goto match_failure statement preceded by the flags test seen below.
Hence, this patch (re)introduces it.

[1] <http://pubs.opengroup.org/onlinepubs/009695399/functions/fwscanf.html>

diff --git a/newlib/libc/stdio/vfwscanf.c b/newlib/libc/stdio/vfwscanf.c
index 0464b0837..ffb6cc85b 100644
--- a/newlib/libc/stdio/vfwscanf.c
+++ b/newlib/libc/stdio/vfwscanf.c
@@ -602,6 +602,7 @@ __SVFWSCANF_R (struct _reent *rptr,
 	case L'*':
 	  if ((flags & (CHAR | SHORT | LONG | LONGDBL | SUPPRESS | MALLOC))
 	      || width)
+	    goto match_failure;
 	  flags |= SUPPRESS;
 	  goto again;
 	case L'l':

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