royitaqi 8e8da88d46 [lldb] Fix SIGSEGV in GetPtraceScope() in Procfs.cpp (#142224) ...

# Symptom

We have seen SIGSEGV like this:
```
* thread #1, name = 'lldb-server', stop reason = SIGSEGV
    frame #0: 0x00007f39e529c993 libc.so.6`__pthread_kill_internal(signo=11, threadid=<unavailable>) at pthread_kill.c:46:37
    ...
  * frame #5: 0x000056027c94fe48 lldb-server`lldb_private::process_linux::GetPtraceScope() + 72
    frame #6: 0x000056027c92f94f lldb-server`lldb_private::process_linux::NativeProcessLinux::Attach(int) + 1087
    ...
```
See [full stack trace](https://pastebin.com/X0d6QhYj).

This happens on Linux where LLDB doesn't have access to
`/proc/sys/kernel/yama/ptrace_scope`.

A similar error (an unchecked `Error`) can be reproduced by running the
newly added unit test without the fix. See the "Test" section below.


# Root cause

`GetPtraceScope()`
([code](328f40f408/lldb/source/Plugins/Process/Linux/Procfs.cpp (L77)))
has the following `if` statement:
```
llvm::Expected<int> lldb_private::process_linux::GetPtraceScope() {
  ErrorOr<std::unique_ptr<MemoryBuffer>> ptrace_scope_file =
      getProcFile("sys/kernel/yama/ptrace_scope");
  if (!*ptrace_scope_file)
    return errorCodeToError(ptrace_scope_file.getError());
  ...
}
```

The intention of the `if` statement is to check whether the
`ptrace_scope_file` is an `Error` or not, and return the error if it is.
However, the `operator*` of `ErrorOr` returns the value that is stored
(which is a `std::unique_ptr<MemoryBuffer>`), so what the `if` condition
actually do is to check if the unique pointer is non-null.

Note that the method `ErrorOr::getStorage()` ([called
by](328f40f408/llvm/include/llvm/Support/ErrorOr.h (L162-L164))
`ErrorOr::operator *`) **does** assert on whether or not `HasError` has
been set (see
[ErrorOr.h](328f40f408/llvm/include/llvm/Support/ErrorOr.h (L235-L243))).
However, it seems this wasn't executed, probably because the LLDB was a
release build.

# Fix

The fix is simply remove the `*` in the said `if` statement.

2025-06-02 10:43:58 -07:00

3.0 KiB

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