llvm-project

8e8da88d - [lldb] Fix SIGSEGV in `GetPtraceScope()` in `Procfs.cpp` (#142224)

[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](https://github.com/llvm/llvm-project/blob/328f40f408c218f25695ea42c844e43bef38660b/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](https://github.com/llvm/llvm-project/blob/328f40f408c218f25695ea42c844e43bef38660b/llvm/include/llvm/Support/ErrorOr.h#L162-L164) `ErrorOr::operator *`) **does** assert on whether or not `HasError` has been set (see [ErrorOr.h](https://github.com/llvm/llvm-project/blob/328f40f408c218f25695ea42c844e43bef38660b/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.