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Fix segfault on infinite recursion in some cases 

This fixes a segfault on infinite function call recursion (rather than
infinite thunk recursion) by tracking the function call depth in
`EvalState`.

Additionally, to avoid printing extremely long stack traces, stack
frames are now deduplicated, with a `(19997 duplicate traces omitted)`
message. This should only really be triggered in infinite recursion
scenarios.

Before:

    $ nix-instantiate --eval --expr '(x: x x) (x: x x)'
    Segmentation fault: 11

After:

    $ nix-instantiate --eval --expr '(x: x x) (x: x x)'
    error: stack overflow

           at «string»:1:14:
                1| (x: x x) (x: x x)
                 |              ^

    $ nix-instantiate --eval --expr '(x: x x) (x: x x)' --show-trace
    error:
           … from call site
             at «string»:1:1:
                1| (x: x x) (x: x x)
                 | ^

           … while calling anonymous lambda
             at «string»:1:2:
                1| (x: x x) (x: x x)
                 |  ^

           … from call site
             at «string»:1:5:
                1| (x: x x) (x: x x)
                 |     ^

           … while calling anonymous lambda
             at «string»:1:11:
                1| (x: x x) (x: x x)
                 |           ^

           … from call site
             at «string»:1:14:
                1| (x: x x) (x: x x)
                 |              ^

           (19997 duplicate traces omitted)

           error: stack overflow
           at «string»:1:14:
                1| (x: x x) (x: x x)
                 |              ^
This commit is contained in:
Rebecca Turner 2023-12-15 11:52:21 -08:00
parent a21c762dab
commit 7434caca05
No known key found for this signature in database
12 changed files with 358 additions and 4 deletions
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32
doc/manual/rl-next/stack-overflow-segfaults.md Normal file
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@ -0,0 +1,32 @@
---
synopsis: Some stack overflow segfaults are fixed
issues: 9616
prs: 9617
---
The number of nested function calls has been restricted, to detect and report
infinite function call recursions. The default maximum call depth is 10,000 and
can be set with [the `max-call-depth`
option](@docroot@/command-ref/conf-file.md#conf-max-call-depth).
This fixes segfaults or the following unhelpful error message in many cases:
error: stack overflow (possible infinite recursion)
Before:
```
$ nix-instantiate --eval --expr '(x: x x) (x: x x)'
Segmentation fault: 11
```
After:
```
$ nix-instantiate --eval --expr '(x: x x) (x: x x)'
error: stack overflow
at «string»:1:14:
1| (x: x x) (x: x x)
| ^
```

3
src/libexpr/eval-settings.hh
View File

@ -124,6 +124,9 @@ struct EvalSettings : Config
Setting<bool> traceVerbose{this, false, "trace-verbose",
"Whether `builtins.traceVerbose` should trace its first argument when evaluated."};
Setting<unsigned int> maxCallDepth{this, 10000, "max-call-depth",
"The maximum function call depth to allow before erroring."};
};
extern EvalSettings evalSettings;

18
src/libexpr/eval.cc
View File

@ -1505,9 +1505,27 @@ void ExprLambda::eval(EvalState & state, Env & env, Value & v)
v.mkLambda(&env, this);
}
namespace {
/** Increments a count on construction and decrements on destruction.
*/
class CallDepth {
size_t & count;
public:
CallDepth(size_t & count) : count(count) {
++count;
}
~CallDepth() {
--count;
}
};
};
void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const PosIdx pos)
{
if (callDepth > evalSettings.maxCallDepth)
error("stack overflow; max-call-depth exceeded").atPos(pos).template debugThrow<EvalError>();
CallDepth _level(callDepth);
auto trace = evalSettings.traceFunctionCalls
? std::make_unique<FunctionCallTrace>(positions[pos])
: nullptr;

5
src/libexpr/eval.hh
View File

@ -622,6 +622,11 @@ private:
const SourcePath & basePath,
std::shared_ptr<StaticEnv> & staticEnv);
/**
* Current Nix call stack depth, used with `max-call-depth` setting to throw stack overflow hopefully before we run out of system stack.
*/
size_t callDepth = 0;
public:
/**

111
src/libutil/error.cc
View File

@ -50,6 +50,32 @@ std::ostream & operator <<(std::ostream & str, const AbstractPos & pos)
return str;
}
/**
* An arbitrarily defined value comparison for the purpose of using traces in the key of a sorted container.
*/
inline bool operator<(const Trace& lhs, const Trace& rhs)
{
// `std::shared_ptr` does not have value semantics for its comparison
// functions, so we need to check for nulls and compare the dereferenced
// values here.
if (lhs.pos != rhs.pos) {
if (!lhs.pos)
return true;
if (!rhs.pos)
return false;
if (*lhs.pos != *rhs.pos)
return *lhs.pos < *rhs.pos;
}
// This formats a freshly formatted hint string and then throws it away, which
// shouldn't be much of a problem because it only runs when pos is equal, and this function is
// used for trace printing, which is infrequent.
return std::forward_as_tuple(lhs.hint.str(), lhs.frame)
< std::forward_as_tuple(rhs.hint.str(), rhs.frame);
}
inline bool operator> (const Trace& lhs, const Trace& rhs) { return rhs < lhs; }
inline bool operator<=(const Trace& lhs, const Trace& rhs) { return !(lhs > rhs); }
inline bool operator>=(const Trace& lhs, const Trace& rhs) { return !(lhs < rhs); }
std::optional<LinesOfCode> AbstractPos::getCodeLines() const
{
if (line == 0)
@ -185,6 +211,69 @@ static bool printPosMaybe(std::ostream & oss, std::string_view indent, const std
return hasPos;
}
void printTrace(
std::ostream & output,
const std::string_view & indent,
size_t & count,
const Trace & trace)
{
output << "\n" << "… " << trace.hint.str() << "\n";
if (printPosMaybe(output, indent, trace.pos))
count++;
}
void printSkippedTracesMaybe(
std::ostream & output,
const std::string_view & indent,
size_t & count,
std::vector<Trace> & skippedTraces,
std::set<Trace> tracesSeen)
{
if (skippedTraces.size() > 0) {
// If we only skipped a few frames, print them out normally;
// messages like "1 duplicate frames omitted" aren't helpful.
if (skippedTraces.size() <= 5) {
for (auto & trace : skippedTraces) {
printTrace(output, indent, count, trace);
}
} else {
output << "\n" << ANSI_WARNING "(" << skippedTraces.size() << " duplicate frames omitted)" ANSI_NORMAL << "\n";
// Clear the set of "seen" traces after printing a chunk of
// `duplicate frames omitted`.
//
// Consider a mutually recursive stack trace with:
// - 10 entries of A
// - 10 entries of B
// - 10 entries of A
//
// If we don't clear `tracesSeen` here, we would print output like this:
// - 1 entry of A
// - (9 duplicate frames omitted)
// - 1 entry of B
// - (19 duplicate frames omitted)
//
// This would obscure the control flow, which went from A,
// to B, and back to A again.
//
// In contrast, if we do clear `tracesSeen`, the output looks like this:
// - 1 entry of A
// - (9 duplicate frames omitted)
// - 1 entry of B
// - (9 duplicate frames omitted)
// - 1 entry of A
// - (9 duplicate frames omitted)
//
// See: `tests/functional/lang/eval-fail-mutual-recursion.nix`
tracesSeen.clear();
}
}
// We've either printed each trace in `skippedTraces` normally, or
// printed a chunk of `duplicate frames omitted`. Either way, we've
// processed these traces and can clear them.
skippedTraces.clear();
}
std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool showTrace)
{
std::string prefix;
@ -333,7 +422,13 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
bool frameOnly = false;
if (!einfo.traces.empty()) {
// Stack traces seen since we last printed a chunk of `duplicate frames
// omitted`.
std::set<Trace> tracesSeen;
// A consecutive sequence of stack traces that are all in `tracesSeen`.
std::vector<Trace> skippedTraces;
size_t count = 0;
for (const auto & trace : einfo.traces) {
if (trace.hint.str().empty()) continue;
if (frameOnly && !trace.frame) continue;
@ -343,14 +438,21 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
break;
}
if (tracesSeen.count(trace)) {
skippedTraces.push_back(trace);
continue;
}
tracesSeen.insert(trace);
printSkippedTracesMaybe(oss, ellipsisIndent, count, skippedTraces, tracesSeen);
count++;
frameOnly = trace.frame;
oss << "\n" << "… " << trace.hint.str() << "\n";
if (printPosMaybe(oss, ellipsisIndent, trace.pos))
count++;
printTrace(oss, ellipsisIndent, count, trace);
}
printSkippedTracesMaybe(oss, ellipsisIndent, count, skippedTraces, tracesSeen);
oss << "\n" << prefix;
}
@ -369,4 +471,5 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
return out;
}
}

8
src/libutil/error.hh
View File

@ -25,6 +25,7 @@
#include <memory>
#include <map>
#include <optional>
#include <compare>
#include <sys/types.h>
#include <sys/stat.h>
@ -88,6 +89,8 @@ struct AbstractPos
std::optional<LinesOfCode> getCodeLines() const;
virtual ~AbstractPos() = default;
inline auto operator<=>(const AbstractPos& rhs) const = default;
};
std::ostream & operator << (std::ostream & str, const AbstractPos & pos);
@ -103,6 +106,11 @@ struct Trace {
bool frame;
};
inline bool operator<(const Trace& lhs, const Trace& rhs);
inline bool operator> (const Trace& lhs, const Trace& rhs);
inline bool operator<=(const Trace& lhs, const Trace& rhs);
inline bool operator>=(const Trace& lhs, const Trace& rhs);
struct ErrorInfo {
Verbosity level;
hintformat msg;

44
tests/functional/lang/eval-fail-duplicate-traces.err.exp Normal file
View File

@ -0,0 +1,44 @@
error:
… from call site
at /pwd/lang/eval-fail-duplicate-traces.nix:9:3:
8| in
9| throwAfter 2
| ^
10|
… while calling 'throwAfter'
at /pwd/lang/eval-fail-duplicate-traces.nix:4:16:
3| let
4| throwAfter = n:
| ^
5| if n > 0
… from call site
at /pwd/lang/eval-fail-duplicate-traces.nix:6:10:
5| if n > 0
6| then throwAfter (n - 1)
| ^
7| else throw "Uh oh!";
… while calling 'throwAfter'
at /pwd/lang/eval-fail-duplicate-traces.nix:4:16:
3| let
4| throwAfter = n:
| ^
5| if n > 0
… from call site
at /pwd/lang/eval-fail-duplicate-traces.nix:6:10:
5| if n > 0
6| then throwAfter (n - 1)
| ^
7| else throw "Uh oh!";
… while calling 'throwAfter'
at /pwd/lang/eval-fail-duplicate-traces.nix:4:16:
3| let
4| throwAfter = n:
| ^
5| if n > 0
error: Uh oh!

9
tests/functional/lang/eval-fail-duplicate-traces.nix Normal file
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@ -0,0 +1,9 @@
# Check that we only omit duplicate stack traces when there's a bunch of them.
# Here, there's only a couple duplicate entries, so we output them all.
let
throwAfter = n:
if n > 0
then throwAfter (n - 1)
else throw "Uh oh!";
in
throwAfter 2

38
tests/functional/lang/eval-fail-infinite-recursion-lambda.err.exp Normal file
View File

@ -0,0 +1,38 @@
error:
… from call site
at /pwd/lang/eval-fail-infinite-recursion-lambda.nix:1:1:
1| (x: x x) (x: x x)
| ^
2|
… while calling anonymous lambda
at /pwd/lang/eval-fail-infinite-recursion-lambda.nix:1:2:
1| (x: x x) (x: x x)
| ^
2|
… from call site
at /pwd/lang/eval-fail-infinite-recursion-lambda.nix:1:5:
1| (x: x x) (x: x x)
| ^
2|
… while calling anonymous lambda
at /pwd/lang/eval-fail-infinite-recursion-lambda.nix:1:11:
1| (x: x x) (x: x x)
| ^
2|
… from call site
at /pwd/lang/eval-fail-infinite-recursion-lambda.nix:1:14:
1| (x: x x) (x: x x)
| ^
2|
(19997 duplicate frames omitted)
error: stack overflow; max-call-depth exceeded
at /pwd/lang/eval-fail-infinite-recursion-lambda.nix:1:14:
1| (x: x x) (x: x x)
| ^
2|

1
tests/functional/lang/eval-fail-infinite-recursion-lambda.nix Normal file
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@ -0,0 +1 @@
(x: x x) (x: x x)

57
tests/functional/lang/eval-fail-mutual-recursion.err.exp Normal file
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@ -0,0 +1,57 @@
error:
… from call site
at /pwd/lang/eval-fail-mutual-recursion.nix:36:3:
35| in
36| throwAfterA true 10
| ^
37|
… while calling 'throwAfterA'
at /pwd/lang/eval-fail-mutual-recursion.nix:29:26:
28|
29| throwAfterA = recurse: n:
| ^
30| if n > 0
… from call site
at /pwd/lang/eval-fail-mutual-recursion.nix:31:10:
30| if n > 0
31| then throwAfterA recurse (n - 1)
| ^
32| else if recurse
(19 duplicate frames omitted)
… from call site
at /pwd/lang/eval-fail-mutual-recursion.nix:33:10:
32| else if recurse
33| then throwAfterB true 10
| ^
34| else throw "Uh oh!";
… while calling 'throwAfterB'
at /pwd/lang/eval-fail-mutual-recursion.nix:22:26:
21| let
22| throwAfterB = recurse: n:
| ^
23| if n > 0
… from call site
at /pwd/lang/eval-fail-mutual-recursion.nix:24:10:
23| if n > 0
24| then throwAfterB recurse (n - 1)
| ^
25| else if recurse
(19 duplicate frames omitted)
… from call site
at /pwd/lang/eval-fail-mutual-recursion.nix:26:10:
25| else if recurse
26| then throwAfterA false 10
| ^
27| else throw "Uh oh!";
(21 duplicate frames omitted)
error: Uh oh!

36
tests/functional/lang/eval-fail-mutual-recursion.nix Normal file
View File

@ -0,0 +1,36 @@
# Check that stack frame deduplication only affects consecutive intervals, and
# that they are reported independently of any preceding sections, even if
# they're indistinguishable.
#
# In terms of the current implementation, we check that we clear the set of
# "seen frames" after eliding a group of frames.
#
# Suppose we have:
# - 10 frames in a function A
# - 10 frames in a function B
# - 10 frames in a function A
#
# We want to output:
# - a few frames of A (skip the rest)
# - a few frames of B (skip the rest)
# - a few frames of A (skip the rest)
#
# If we implemented this in the naive manner, we'd instead get:
# - a few frames of A (skip the rest)
# - a few frames of B (skip the rest, _and_ skip the remaining frames of A)
let
throwAfterB = recurse: n:
if n > 0
then throwAfterB recurse (n - 1)
else if recurse
then throwAfterA false 10
else throw "Uh oh!";
throwAfterA = recurse: n:
if n > 0
then throwAfterA recurse (n - 1)
else if recurse
then throwAfterB true 10
else throw "Uh oh!";
in
throwAfterA true 10