Messages in this thread Patch in this message | | | From | Rasmus Villemoes <> | Subject | [PATCH 06/13] lib/vsprintf.c: warn about too large precisions and field widths | Date | Tue, 20 Oct 2015 22:30:06 +0200 |
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The field width is overloaded to pass some extra information for some %p extensions (e.g. #bits for %pb). But we might silently truncate the passed value when we stash it in struct printf_spec (see e.g. "lib/vsprintf.c: expand field_width to 24 bits"). Hopefully 23 value bits should now be enough for everybody, but if not, let's make some noise.
Do the same for the precision. In both cases, clamping seems more sensible than truncating. A negative precision is the same as 0, so use that as lower bound. For the field width, the smallest representable value is actually -(1<<23), but a negative field width means 'set the LEFT flag and use the absolute value', so we want the absolute value to fit.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> --- lib/vsprintf.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 6d75a3364683..3e96cf45c681 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -386,6 +386,8 @@ struct printf_spec { unsigned int base:8; /* number base, 8, 10 or 16 only */ signed int precision:16; /* # of digits/chars */ }; +#define FIELD_WIDTH_MAX ((1 << 23) - 1) +#define PRECISION_MAX ((1 << 15) - 1) extern char __check_printf_spec[1-2*(sizeof(struct printf_spec) != 8)]; static noinline_for_stack @@ -1813,6 +1815,24 @@ qualifier: return ++fmt - start; } +static inline void +set_field_width(struct printf_spec *spec, int width) +{ + spec->field_width = width; + if (WARN_ONCE(spec->field_width != width, "field width %d too large", width)) { + spec->field_width = clamp(width, -FIELD_WIDTH_MAX, FIELD_WIDTH_MAX); + } +} + +static inline void +set_precision(struct printf_spec *spec, int prec) +{ + spec->precision = prec; + if (WARN_ONCE(spec->precision != prec, "precision %d too large", prec)) { + spec->precision = clamp(prec, 0, PRECISION_MAX); + } +} + /** * vsnprintf - Format a string and place it in a buffer * @buf: The buffer to place the result into @@ -1905,11 +1925,11 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args) } case FORMAT_TYPE_WIDTH: - spec.field_width = va_arg(args, int); + set_field_width(&spec, va_arg(args, int)); break; case FORMAT_TYPE_PRECISION: - spec.precision = va_arg(args, int); + set_precision(&spec, va_arg(args, int)); break; case FORMAT_TYPE_CHAR: { -- 2.6.1
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