Do not warn on correct use of the '%n' format specifier.
While '%n' can be used for evil in an attacker-controlled format string, there
isn't any acute danger in using it in a literal format string with an argument
of the appropriate type.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@160984 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index eb8fcbb..a58f901 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -5327,9 +5327,6 @@
def note_array_index_out_of_bounds : Note<
"array %0 declared here">;
-def warn_printf_write_back : Warning<
- "use of '%%n' in format string discouraged (potentially insecure)">,
- InGroup<FormatSecurity>;
def warn_printf_insufficient_data_args : Warning<
"more '%%' conversions than data arguments">, InGroup<Format>;
def warn_printf_data_arg_not_used : Warning<
diff --git a/lib/Sema/SemaChecking.cpp b/lib/Sema/SemaChecking.cpp
index 200b943..dce912c 100644
--- a/lib/Sema/SemaChecking.cpp
+++ b/lib/Sema/SemaChecking.cpp
@@ -2561,15 +2561,6 @@
HandleNonStandardConversionSpecification(LM, CS, startSpecifier,
specifierLen);
- // Are we using '%n'?
- if (CS.getKind() == ConversionSpecifier::nArg) {
- // Issue a warning about this being a possible security issue.
- EmitFormatDiagnostic(S.PDiag(diag::warn_printf_write_back),
- getLocationOfByte(CS.getStart()),
- /*IsStringLocation*/true,
- getSpecifierRange(startSpecifier, specifierLen));
- }
-
// The remaining checks depend on the data arguments.
if (HasVAListArg)
return true;
diff --git a/test/Sema/format-strings.c b/test/Sema/format-strings.c
index 9da5f9b..d351258 100644
--- a/test/Sema/format-strings.c
+++ b/test/Sema/format-strings.c
@@ -88,10 +88,8 @@
{
int x;
char *b;
-
- printf("%n",&x); // expected-warning {{'%n' in format string discouraged}}
- sprintf(b,"%d%%%n",1, &x); // expected-warning {{'%n' in format string dis}}
- printf("%n",b); // expected-warning {{'%n' in format string discouraged}} expected-warning{{format specifies type 'int *' but the argument has type 'char *'}}
+ printf("%n", b); // expected-warning{{format specifies type 'int *' but the argument has type 'char *'}}
+ printf("%n", &x); // no-warning
}
void check_invalid_specifier(FILE* fp, char *buf)
@@ -168,7 +166,6 @@
int x;
printf(P); // expected-warning {{format string is not a string literal (potentially insecure)}}
printf(P, 42);
- printf("%n", &x); // expected-warning {{use of '%n' in format string discouraged }}
}
void torture(va_list v8) {
@@ -186,7 +183,6 @@
printf("%*d\n", f, x); // expected-warning{{field width should have type 'int', but argument has type 'double'}}
printf("%*.*d\n", x, f, x); // expected-warning{{field precision should have type 'int', but argument has type 'double'}}
printf("%**\n"); // expected-warning{{invalid conversion specifier '*'}}
- printf("%n", &i); // expected-warning{{use of '%n' in format string discouraged (potentially insecure)}}
printf("%d%d\n", x); // expected-warning{{more '%' conversions than data arguments}}
printf("%d\n", x, x); // expected-warning{{data argument not used by format string}}
printf("%W%d%Z\n", x, x, x); // expected-warning{{invalid conversion specifier 'W'}} expected-warning{{invalid conversion specifier 'Z'}}
@@ -317,14 +313,14 @@
// Bad flag usage
printf("%#p", (void *) 0); // expected-warning{{flag '#' results in undefined behavior with 'p' conversion specifier}}
printf("%0d", -1); // no-warning
- printf("%#n", (int *) 0); // expected-warning{{flag '#' results in undefined behavior with 'n' conversion specifier}} expected-warning{{use of '%n' in format string discouraged (potentially insecure)}}
- printf("%-n", (int *) 0); // expected-warning{{flag '-' results in undefined behavior with 'n' conversion specifier}} expected-warning{{use of '%n' in format string discouraged (potentially insecure)}}
+ printf("%#n", (int *) 0); // expected-warning{{flag '#' results in undefined behavior with 'n' conversion specifier}}
+ printf("%-n", (int *) 0); // expected-warning{{flag '-' results in undefined behavior with 'n' conversion specifier}}
printf("%-p", (void *) 0); // no-warning
// Bad optional amount use
printf("%.2c", 'a'); // expected-warning{{precision used with 'c' conversion specifier, resulting in undefined behavior}}
- printf("%1n", (int *) 0); // expected-warning{{field width used with 'n' conversion specifier, resulting in undefined behavior}} expected-warning{{use of '%n' in format string discouraged (potentially insecure)}}
- printf("%.9n", (int *) 0); // expected-warning{{precision used with 'n' conversion specifier, resulting in undefined behavior}} expected-warning{{use of '%n' in format string discouraged (potentially insecure)}}
+ printf("%1n", (int *) 0); // expected-warning{{field width used with 'n' conversion specifier, resulting in undefined behavior}}
+ printf("%.9n", (int *) 0); // expected-warning{{precision used with 'n' conversion specifier, resulting in undefined behavior}}
// Ignored flags
printf("% +f", 1.23); // expected-warning{{flag ' ' is ignored when flag '+' is present}}
@@ -436,11 +432,6 @@
printf(kFormat2, 1, "foo"); // expected-warning{{data argument position '18' exceeds the number of data arguments (2)}}
printf("%18$s\n", 1, "foo"); // expected-warning{{data argument position '18' exceeds the number of data arguments (2)}}
- const char kFormat3[] = "%n"; // expected-note{{format string is defined here}}
- printf(kFormat3, (int*)NULL); // expected-warning{{use of '%n' in format string discouraged}}
- printf("%n", (int*)NULL); // expected-warning{{use of '%n' in format string discouraged}}
-
-
const char kFormat4[] = "%y"; // expected-note{{format string is defined here}}
printf(kFormat4, 5); // expected-warning{{invalid conversion specifier 'y'}}
printf("%y", 5); // expected-warning{{invalid conversion specifier 'y'}}
