lib/vsprintf.c: improve standard conformance of sscanf()

Xen's pciback points out a couple of deficiencies with vsscanf()'s
standard conformance:

- Trailing character matching cannot be checked by the caller: With a
  format string of "(%x:%x.%x) %n" absence of the closing parenthesis
  cannot be checked, as input of "(00:00.0)" doesn't cause the %n to be
  evaluated (because of the code not skipping white space before the
  trailing %n).

- The parameter corresponding to a trailing %n could get filled even if
  there was a matching error: With a format string of "(%x:%x.%x)%n",
  input of "(00:00.0]" would still fill the respective variable pointed to
  (and hence again make the mismatch non-detectable by the caller).

This patch aims at fixing those, but leaves other non-conforming aspects
of it untouched, among them these possibly relevant ones:

- improper handling of the assignment suppression character '*' (blindly
  discarding all succeeding non-white space from the format and input
  strings),

- not honoring conversion specifiers for %n, - not recognizing the C99
  conversion specifier 't' (recognized by vsprintf()).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d4cce101083c4bc11a5ea5d8df7576c042597990..6a09556e3f378c0262784a6b5b7288d08caf0e19 100644 (file)
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2019,7 +2019,7 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
        s16 field_width;
        bool is_sign;
 
-       while (*fmt && *str) {
+       while (*fmt) {
                /* skip any white space in format */
                /* white space in format matchs any amount of
                 * white space, including none, in the input.
@@ -2044,6 +2044,8 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
                 * advance both strings to next white space
                 */
                if (*fmt == '*') {
+                       if (!*str)
+                               break;
                        while (!isspace(*fmt) && *fmt != '%' && *fmt)
                                fmt++;
                        while (!isspace(*str) && *str)
@@ -2072,7 +2074,17 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
                        }
                }
 
-               if (!*fmt || !*str)
+               if (!*fmt)
+                       break;
+
+               if (*fmt == 'n') {
+                       /* return number of characters read so far */
+                       *va_arg(args, int *) = str - buf;
+                       ++fmt;
+                       continue;
+               }
+
+               if (!*str)
                        break;
 
                base = 10;
@@ -2105,13 +2117,6 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
                        num++;
                }
                continue;
-               case 'n':
-                       /* return number of characters read so far */
-               {
-                       int *i = (int *)va_arg(args, int*);
-                       *i = str - buf;
-               }
-               continue;
                case 'o':
                        base = 8;
                        break;
@@ -2212,16 +2217,6 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
                str = next;
        }
 
-       /*
-        * Now we've come all the way through so either the input string or the
-        * format ended. In the former case, there can be a %n at the current
-        * position in the format that needs to be filled.
-        */
-       if (*fmt == '%' && *(fmt + 1) == 'n') {
-               int *p = (int *)va_arg(args, int *);
-               *p = str - buf;
-       }
-
        return num;
 }
 EXPORT_SYMBOL(vsscanf);