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[lldb][Linux] Fix checking of error values when attach fails #161673
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Relates to llvm#161510 (it's not fixing it, it's just making the error not be an unhandled error) When we fail to attach to a process we see if we can add more information about why it happpened: ``` if (status.GetError() == EPERM) { // Depending on the value of ptrace_scope, we can return a different // error that suggests how to fix it. return AddPtraceScopeNote(status.ToError()); } ``` ToError creates a new error value and leaves the one in `status` unchecked. `status`'s error is ok because it will be checked by Status' destructor. The problem happens in `AddPtraceScopeNote`. If we take certain return paths, this new error, or the one we get when trying to find the ptrace scope, may be unchecked on destruction when the function returns. To fix this, in AddPtraceScopeNote, consume any errors that we are not going to return. Anything returned will be checked by some caller. Reproducing this failure mode is difficult but it can be faked by calling AddPtraceScopeNote earlier. Which is what I did to prove the concept of the problem.
@llvm/pr-subscribers-lldb Author: David Spickett (DavidSpickett) ChangesRelates to #161510 (it's not fixing it, it's just making the error not be an unhandled error) When we fail to attach to a process we see if we can add more information about why it happened:
ToError creates a new error value and leaves the one in The problem happens in To fix this, in AddPtraceScopeNote, consume any errors that we are not going to return. Anything returned will be checked by some caller. Reproducing this failure mode is difficult but it can be faked by calling AddPtraceScopeNote earlier. Which is what I did to prove the concept of the problem. Full diff: https://github.com/llvm/llvm-project/pull/161673.diff 1 Files Affected:
diff --git a/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp b/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
index 9c798cb1cc8f2..7d0bca738e2e5 100644
--- a/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
+++ b/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
@@ -219,7 +219,8 @@ static llvm::Error AddPtraceScopeNote(llvm::Error original_error) {
Expected<int> ptrace_scope = GetPtraceScope();
if (auto E = ptrace_scope.takeError()) {
Log *log = GetLog(POSIXLog::Process);
- LLDB_LOG(log, "error reading value of ptrace_scope: {0}", E);
+ LLDB_LOG(log, "error reading value of ptrace_scope: {0}",
+ llvm::toString(std::move(E)));
// The original error is probably more interesting than not being able to
// read or interpret ptrace_scope.
@@ -230,6 +231,7 @@ static llvm::Error AddPtraceScopeNote(llvm::Error original_error) {
switch (*ptrace_scope) {
case 1:
case 2:
+ llvm::consumeError(std::move(original_error));
return llvm::createStringError(
std::error_code(errno, std::generic_category()),
"The current value of ptrace_scope is %d, which can cause ptrace to "
@@ -239,6 +241,7 @@ static llvm::Error AddPtraceScopeNote(llvm::Error original_error) {
"https://www.kernel.org/doc/Documentation/security/Yama.txt.",
*ptrace_scope);
case 3:
+ llvm::consumeError(std::move(original_error));
return llvm::createStringError(
std::error_code(errno, std::generic_category()),
"The current value of ptrace_scope is 3, which will cause ptrace to "
|
The Yama error now looks like:
|
Relates to #161510
Fixes 6db44e5
(it's not fixing it, it's just making the error not be an unhandled error)
When we fail to attach to a process we see if we can add more information about why it happened:
ToError creates a new error value and leaves the one in
status
unchecked.status
's error is ok because it will be checked by Status' destructor.The problem happens in
AddPtraceScopeNote
. If we take certain return paths, this new error, or the one we get when trying to find the ptrace scope, may be unchecked on destruction when the function returns.To fix this, in AddPtraceScopeNote, consume any errors that we are not going to return. Anything returned will be checked by some caller.
Reproducing this failure mode is difficult but it can be faked by calling AddPtraceScopeNote earlier. Which is what I did to prove the concept of the problem.