Skip to content

C++: Mark the write to fprintf's 0'th argument as partial #20242

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
MathiasVP merged 3 commits into from
Aug 19, 2025
Merged

C++: Mark the write to fprintf's 0'th argument as partial #20242

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
4551875
C++: Drive-by improvement: Use 'partialFlowFunc' since it is in scope…
MathiasVP Aug 18, 2025
6a57da7
C++: Add a test with missing flow.
MathiasVP Aug 18, 2025
af00e46
C++: Mark fprintf and friends as a partial write of the stream argument.
MathiasVP Aug 18, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 2 additions & 2 deletions cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaImpl.qll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -756,9 +756,9 @@ private predicate modeledFlowBarrier(Node n) {
partialFlowFunc = call.getStaticCallTarget() and
not partialFlowFunc.isPartialWrite(output)
|
call.getStaticCallTarget().(DataFlow::DataFlowFunction).hasDataFlow(_, output)
partialFlowFunc.(DataFlow::DataFlowFunction).hasDataFlow(_, output)
or
call.getStaticCallTarget().(Taint::TaintFunction).hasTaintFlow(_, output)
partialFlowFunc.(Taint::TaintFunction).hasTaintFlow(_, output)
)
or
exists(Operand operand, Instruction instr, Node n0, int indirectionIndex |
Expand Down
10 changes: 10 additions & 0 deletions cpp/ql/lib/semmle/code/cpp/models/interfaces/FormattingFunction.qll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,16 @@ abstract class FormattingFunction extends ArrayFunction, TaintFunction {
output.isParameterDeref(this.getOutputParameterIndex(_))
)
}

final override predicate isPartialWrite(FunctionOutput output) {
exists(int outputParameterIndex |
output.isParameterDeref(outputParameterIndex) and
Copy link
Copy Markdown
Contributor

@jketema jketema Aug 19, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Given where you added this, this presumably also leads more flow on the first argument of functions like sprintf. Is that correct? If so, is that what we want?

Copy link
Copy Markdown
Contributor Author

@MathiasVP MathiasVP Aug 19, 2025 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The this.getOutputParameterIndex(true) conjunct only holds for formatting functions which specify that the output parameter is a stream, and sprintf implements this predicate with isStream = false. So this shouldn't affect sprintf.

Copy link
Copy Markdown
Contributor

@jketema jketema Aug 19, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Thanks for the clarification!

// We require the output to be a stream since that definitely means that
// it's a partial write. If it's not a stream then it will most likely
// fill the whole buffer.
Comment thread
MathiasVP marked this conversation as resolved.
outputParameterIndex = this.getOutputParameterIndex(true)
)
}
}

/**
Expand Down
4 changes: 4 additions & 0 deletions cpp/ql/test/library-tests/dataflow/taint-tests/localTaint.expected
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7767,6 +7767,10 @@ WARNING: module 'TaintTracking' has been deprecated and may be removed in future
| taint.cpp:830:20:830:34 | call to indirect_source | taint.cpp:832:23:832:24 | in | |
| taint.cpp:831:15:831:17 | out | taint.cpp:832:18:832:20 | out | |
| taint.cpp:831:15:831:17 | out | taint.cpp:833:8:833:10 | out | |
| taint.cpp:841:21:841:35 | call to indirect_source | taint.cpp:842:11:842:12 | fp | |
| taint.cpp:841:21:841:35 | call to indirect_source | taint.cpp:843:16:843:17 | fp | |
| taint.cpp:842:11:842:12 | ref arg fp | taint.cpp:843:16:843:17 | fp | |
| taint.cpp:842:15:842:16 | | taint.cpp:842:11:842:12 | ref arg fp | TAINT |
| thread.cpp:10:27:10:27 | s | thread.cpp:10:27:10:27 | s | |
| thread.cpp:10:27:10:27 | s | thread.cpp:11:8:11:8 | s | |
| thread.cpp:14:26:14:26 | s | thread.cpp:15:8:15:8 | s | |
Expand Down
11 changes: 11 additions & 0 deletions cpp/ql/test/library-tests/dataflow/taint-tests/taint.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -831,4 +831,15 @@ void test_write_to_const_ptr_ptr() {
const char* out;
take_const_ptr(out, in);
sink(out); // $ SPURIOUS: ast
}

void indirect_sink(FILE *fp);
int fprintf(FILE *fp, const char *format, ...);

int f7(void)
{
FILE* fp = (FILE*)indirect_source();
fprintf(fp, "");
indirect_sink(fp); // $ ir MISSING: ast
return 0;
}
5 changes: 5 additions & 0 deletions cpp/ql/test/library-tests/dataflow/taint-tests/taint.ql
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -117,6 +117,11 @@ module IRTest {
call.getTarget().getName() = "sink" and
[sink.asExpr(), sink.asIndirectExpr()] = call.getAnArgument()
)
or
exists(FunctionCall call |
call.getTarget().getName() = "indirect_sink" and
sink.asIndirectExpr() = call.getAnArgument()
)
}

predicate isBarrier(DataFlow::Node barrier) {
Expand Down
53 changes: 53 additions & 0 deletions cpp/ql/test/library-tests/dataflow/taint-tests/test_mad-signatures.expected
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17670,6 +17670,55 @@ signatureMatches
| taint.cpp:822:6:822:19 | take_const_ptr | (unsigned long *,const char *) | | set_cert_ex | 1 |
| taint.cpp:822:6:822:19 | take_const_ptr | (unsigned long *,const char *) | | set_name_ex | 1 |
| taint.cpp:822:6:822:19 | take_const_ptr | (uv_pipe_t *,const char *) | | uv_pipe_bind | 1 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_default_uflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_feof | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_ferror | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_file_close_mmap | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_file_underflow_mmap | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_ftell | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_getc | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_getwc | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_new_file_underflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_peekc_locked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_str_count | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_str_underflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_sungetc | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_sungetwc | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_wdefault_uflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_wfile_underflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_wfile_underflow_mmap | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_wstr_count | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | _IO_wstr_underflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __fbufsize | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __feof_unlocked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __ferror_unlocked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __fileno | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __flbf | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __fopen_maybe_mmap | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __fpending | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __ftello | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __fwriting | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __getc_unlocked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __getwc_unlocked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __uflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __underflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __wuflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | __wunderflow | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | feof_unlocked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | ferror_unlocked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | fgetc_unlocked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | fgetgrent | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | fgetpwent | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | fgetsgent | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | fgetspent | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | getc_unlocked | 0 |
| taint.cpp:836:6:836:18 | indirect_sink | (FILE *) | | getmntent | 0 |
| taint.cpp:837:5:837:11 | fprintf | (CURLSH *,CURLSHoption,...) | | curl_share_setopt | 2 |
| taint.cpp:837:5:837:11 | fprintf | (Jim_Interp *,const char *,...) | | Jim_SetResultFormatted | 1 |
| taint.cpp:837:5:837:11 | fprintf | (Jim_Interp *,const char *,...) | | Jim_SetResultFormatted | 2 |
| taint.cpp:837:5:837:11 | fprintf | (char **,const char *,...) | | ___asprintf | 1 |
| taint.cpp:837:5:837:11 | fprintf | (char **,const char *,...) | | ___asprintf | 2 |
| taint.cpp:837:5:837:11 | fprintf | (curl_httppost **,curl_httppost **,...) | | curl_formadd | 2 |
| thread.cpp:4:6:4:9 | sink | (int) | | ASN1_STRING_type_new | 0 |
| thread.cpp:4:6:4:9 | sink | (int) | | ASN1_tag2bit | 0 |
| thread.cpp:4:6:4:9 | sink | (int) | | ASN1_tag2str | 0 |
Expand Down Expand Up @@ -47191,6 +47240,10 @@ getParameterTypeName
| taint.cpp:817:6:817:27 | write_to_const_ptr_ptr | 1 | const char ** |
| taint.cpp:822:6:822:19 | take_const_ptr | 0 | const char * |
| taint.cpp:822:6:822:19 | take_const_ptr | 1 | const char * |
| taint.cpp:836:6:836:18 | indirect_sink | 0 | FILE * |
| taint.cpp:837:5:837:11 | fprintf | 0 | FILE * |
| taint.cpp:837:5:837:11 | fprintf | 1 | const char * |
| taint.cpp:837:5:837:11 | fprintf | 2 | ... |
| thread.cpp:4:6:4:9 | sink | 0 | int |
| thread.cpp:6:8:6:8 | operator= | 0 | S && |
| thread.cpp:6:8:6:8 | operator= | 0 | const S & |
Expand Down
Loading