[PATCH v3 1/4] lib: vsprintf: scanf: Negative number must have field width > 1

[Richard Fitzgerald <rf@opensource.cirrus.com>]

If a signed number field starts with a '-' the field width must be > 1,
or unlimited, to allow at least one digit after the '-'.

This patch adds a check for this. If a signed field starts with '-'
and field_width == 1 the scanf will quit.

It is ok for a signed number field to have a field width of 1 if it
starts with a digit. In that case the single digit can be converted.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
---
 lib/vsprintf.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 14c9a6af1b23..8954ff94a53c 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -3433,8 +3433,12 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 		str = skip_spaces(str);
 
 		digit = *str;
-		if (is_sign && digit == '-')
+		if (is_sign && digit == '-') {
+			if (field_width == 1)
+				break;
+
 			digit = *(str + 1);
+		}
 
 		if (!digit
 		    || (base == 16 && !isxdigit(digit))
-- 
2.20.1