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[libc] Scanf shouldn't match just "0x" for hex int #112440

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Oct 18, 2024
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[libc] Scanf shouldn't match just "0x" for hex int #112440

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[libc] Scanf shouldn't match just "0x" for hex int
michaelrj-google Oct 15, 2024
d6b2da9
delete commented-out code
michaelrj-google Oct 17, 2024
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21 changes: 17 additions & 4 deletions libc/src/stdio/scanf_core/int_converter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -124,13 +124,25 @@ int convert_int(Reader *reader, const FormatSection &to_conv) {

if (to_lower(cur_char) == 'x') {
// This is a valid hex prefix.

is_number = false;
// A valid hex prefix is not necessarily a valid number. For the
// conversion to be valid it needs to use all of the characters it
// consumes. From the standard:
// 7.23.6.2 paragraph 9: "An input item is defined as the longest
// sequence of input characters which does not exceed any specified
// field width and which is, or is a prefix of, a matching input
// sequence."
// 7.23.6.2 paragraph 10: "If the input item is not a matching sequence,
// the execution of the directive fails: this condition is a matching
// failure"
base = 16;
if (max_width > 1) {
--max_width;
cur_char = reader->getc();
} else {
write_int_with_length(0, to_conv);
return READ_OK;
// write_int_with_length(0, to_conv);
return MATCHING_FAILURE;
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@nickdesaulniers nickdesaulniers Oct 17, 2024

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Consider making this an early return if you reverse the conditional.

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@michaelrj-google michaelrj-google Oct 17, 2024

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The if (max_width > 1) condition is a common pattern in scanf, so I'd rather keep the consistency and not reverse this conditional.

}

} else {
Expand Down Expand Up @@ -198,6 +210,9 @@ int convert_int(Reader *reader, const FormatSection &to_conv) {
// last one back.
reader->ungetc(cur_char);

if (!is_number)
return MATCHING_FAILURE;

if (has_overflow) {
write_int_with_length(MAX, to_conv);
} else {
Expand All @@ -207,8 +222,6 @@ int convert_int(Reader *reader, const FormatSection &to_conv) {
write_int_with_length(result, to_conv);
}

if (!is_number)
return MATCHING_FAILURE;
return READ_OK;
}

Expand Down
36 changes: 26 additions & 10 deletions libc/test/src/stdio/sscanf_test.cpp
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Expand Up @@ -177,13 +177,25 @@ TEST(LlvmLibcSScanfTest, IntConvMaxLengthTests) {
EXPECT_EQ(ret_val, 1);
EXPECT_EQ(result, 0);

result = -999;

// 0x is a valid prefix, but not a valid number. This should be a matching
// failure and should not modify the values.
ret_val = LIBC_NAMESPACE::sscanf("0x1", "%2i", &result);
EXPECT_EQ(ret_val, 1);
EXPECT_EQ(result, 0);
EXPECT_EQ(ret_val, 0);
EXPECT_EQ(result, -999);

ret_val = LIBC_NAMESPACE::sscanf("-0x1", "%3i", &result);
EXPECT_EQ(ret_val, 0);
EXPECT_EQ(result, -999);

ret_val = LIBC_NAMESPACE::sscanf("0x1", "%3i", &result);
EXPECT_EQ(ret_val, 1);
EXPECT_EQ(result, 0);
EXPECT_EQ(result, 1);

ret_val = LIBC_NAMESPACE::sscanf("-0x1", "%4i", &result);
EXPECT_EQ(ret_val, 1);
EXPECT_EQ(result, -1);

ret_val = LIBC_NAMESPACE::sscanf("-0x123", "%4i", &result);
EXPECT_EQ(ret_val, 1);
Expand Down Expand Up @@ -212,7 +224,7 @@ TEST(LlvmLibcSScanfTest, IntConvNoWriteTests) {
EXPECT_EQ(result, 0);

ret_val = LIBC_NAMESPACE::sscanf("0x1", "%*2i", &result);
EXPECT_EQ(ret_val, 1);
EXPECT_EQ(ret_val, 0);
EXPECT_EQ(result, 0);

ret_val = LIBC_NAMESPACE::sscanf("a", "%*i", &result);
Expand Down Expand Up @@ -679,13 +691,17 @@ TEST(LlvmLibcSScanfTest, CombinedConv) {
EXPECT_EQ(result, 123);
ASSERT_STREQ(buffer, "abc");

result = -1;

// 0x is a valid prefix, but not a valid number. This should be a matching
// failure and should not modify the values.
ret_val = LIBC_NAMESPACE::sscanf("0xZZZ", "%i%s", &result, buffer);
EXPECT_EQ(ret_val, 2);
EXPECT_EQ(result, 0);
ASSERT_STREQ(buffer, "ZZZ");
EXPECT_EQ(ret_val, 0);
EXPECT_EQ(result, -1);
ASSERT_STREQ(buffer, "abc");

ret_val = LIBC_NAMESPACE::sscanf("0xZZZ", "%X%s", &result, buffer);
EXPECT_EQ(ret_val, 2);
EXPECT_EQ(result, 0);
ASSERT_STREQ(buffer, "ZZZ");
EXPECT_EQ(ret_val, 0);
EXPECT_EQ(result, -1);
ASSERT_STREQ(buffer, "abc");
}
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