vsprintf: remove %n handling

All in-kernel users of %n in format strings have now been removed and
the %n directive is ignored.  Remove the handling of %n so that it is
treated the same as any other invalid format string directive.  Keep a
warning in place to deter new instances of %n in format strings.

Signed-off-by: Ryan Mallon <rmallon@gmail.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 36 deletions

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 5e2cf6f342f8..0648291cdafe 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -364,7 +364,6 @@ enum format_type {
         FORMAT_TYPE_SHORT,
         FORMAT_TYPE_UINT,
         FORMAT_TYPE_INT,
-        FORMAT_TYPE_NRCHARS,
         FORMAT_TYPE_SIZE_T,
         FORMAT_TYPE_PTRDIFF
 };
@@ -1538,10 +1537,6 @@ qualifier:
                 return fmt - start;
                 /* skip alnum */
 
-        case 'n':
-                spec->type = FORMAT_TYPE_NRCHARS;
-                return ++fmt - start;
-
         case '%':
                 spec->type = FORMAT_TYPE_PERCENT_CHAR;
                 return ++fmt - start;
@@ -1564,6 +1559,15 @@ qualifier:
         case 'u':
                 break;
 
+        case 'n':
+                /*
+                 * Since %n poses a greater security risk than utility, treat
+                 * it as an invalid format specifier. Warn about its use so
+                 * that new instances don't get added.
+                 */
+                WARN_ONCE(1, "Please remove ignored %%n in '%s'\n", fmt);
+                /* Fall-through */
+
         default:
                 spec->type = FORMAT_TYPE_INVALID;
                 return fmt - start;
@@ -1737,20 +1741,6 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
                         ++str;
                         break;
 
-                case FORMAT_TYPE_NRCHARS: {
-                        /*
-                         * Since %n poses a greater security risk than
-                         * utility, ignore %n and skip its argument.
-                         */
-                        void *skip_arg;
-
-                        WARN_ONCE(1, "Please remove ignored %%n in '%s'\n",
-                                        old_fmt);
-
-                        skip_arg = va_arg(args, void *);
-                        break;
-                }
-
                 default:
                         switch (spec.type) {
                         case FORMAT_TYPE_LONG_LONG:
@@ -2025,19 +2015,6 @@ do {									\
                                 fmt++;
                         break;
 
-                case FORMAT_TYPE_NRCHARS: {
-                        /* skip %n 's argument */
-                        u8 qualifier = spec.qualifier;
-                        void *skip_arg;
-                        if (qualifier == 'l')
-                                skip_arg = va_arg(args, long *);
-                        else if (_tolower(qualifier) == 'z')
-                                skip_arg = va_arg(args, size_t *);
-                        else
-                                skip_arg = va_arg(args, int *);
-                        break;
-                }
-
                 default:
                         switch (spec.type) {
 
@@ -2196,10 +2173,6 @@ int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf)
                         ++str;
                         break;
 
-                case FORMAT_TYPE_NRCHARS:
-                        /* skip */
-                        break;
-
                 default: {
                         unsigned long long num;