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Don't access a C string past precision in printf (#1595)

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This commit is contained in:
Victor Zverovich 2020-04-22 16:39:28 -07:00
parent 7d748a6f82
commit 0463665ef1
2 changed files with 19 additions and 0 deletions
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14
include/fmt/printf.h
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@ -141,6 +141,13 @@ template <typename Context> class char_converter {
void operator()(T) {} // No conversion needed for non-integral types. void operator()(T) {} // No conversion needed for non-integral types.
}; };
// An argument visitor that return a pointer to a C string if argument is a
// string or null otherwise.
template <typename Char> struct get_cstring {
template <typename T> const Char* operator()(T) { return nullptr; }
const Char* operator()(const Char* s) { return s; }
};
// Checks if an argument is a valid printf width specifier and sets // Checks if an argument is a valid printf width specifier and sets
// left alignment if it is negative. // left alignment if it is negative.
template <typename Char> class printf_width_handler { template <typename Char> class printf_width_handler {
@ -495,6 +502,13 @@ OutputIt basic_printf_context<OutputIt, Char>::format() {
} }
format_arg arg = get_arg(arg_index); format_arg arg = get_arg(arg_index);
if (specs.precision >= 0 && arg.type() == internal::type::cstring_type) {
auto str = visit_format_arg(internal::get_cstring<Char>(), arg);
auto end = str + specs.precision;
auto nul = std::find(str, end, Char());
arg = internal::make_arg<basic_printf_context>(basic_string_view<Char>(
str, nul != end ? nul - str : specs.precision));
}
if (specs.alt && visit_format_arg(internal::is_zero_int(), arg)) if (specs.alt && visit_format_arg(internal::is_zero_int(), arg))
specs.alt = false; specs.alt = false;
if (specs.fill[0] == '0') { if (specs.fill[0] == '0') {

5
test/printf-test.cc
View File

@ -259,6 +259,11 @@ TEST(PrintfTest, FloatPrecision) {
EXPECT_PRINTF(buffer, "%.3a", 1234.5678); EXPECT_PRINTF(buffer, "%.3a", 1234.5678);
} }
TEST(PrintfTest, StringPrecision) {
char test[] = {'H', 'e', 'l', 'l', 'o'};
EXPECT_EQ(fmt::sprintf("%.4s", test), "Hell");
}
TEST(PrintfTest, IgnorePrecisionForNonNumericArg) { TEST(PrintfTest, IgnorePrecisionForNonNumericArg) {
EXPECT_PRINTF("abc", "%.5s", "abc"); EXPECT_PRINTF("abc", "%.5s", "abc");
} }