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-rw-r--r--stdio-common/vfprintf.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/stdio-common/vfprintf.c b/stdio-common/vfprintf.c
index 4f0d971c55..20638ad1fd 100644
--- a/stdio-common/vfprintf.c
+++ b/stdio-common/vfprintf.c
@@ -1026,10 +1026,11 @@ vfprintf (FILE *s, const CHAR_T *format, va_list ap)
 	    const char *mbs = (const char *) string;			      \
 	    mbstate_t mbstate;						      \
 									      \
-	    len = prec != -1 ? (size_t) prec : strlen (mbs);		      \
+	    len = prec != -1 ? __strnlen (mbs, (size_t) prec) : strlen (mbs); \
 									      \
 	    /* Allocate dynamically an array which definitely is long	      \
-	       enough for the wide character version.  */		      \
+	       enough for the wide character version.  Each byte in the	      \
+	       multi-byte string can produce at most one wide character.  */  \
 	    if (__libc_use_alloca (len * sizeof (wchar_t)))		      \
 	      string = (CHAR_T *) alloca (len * sizeof (wchar_t));	      \
 	    else if ((string = (CHAR_T *) malloc (len * sizeof (wchar_t)))    \