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Fixed memory limit bypass using mremap #42

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Fixed memory limit bypass using mremap #42

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63 changes: 41 additions & 22 deletions src/limits/MemoryLimitListener.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -40,33 +40,52 @@ MemoryLimitListener::MemoryLimitListener(uint64_t memoryLimitKb)
if (!vmPeakValid_) {
return tracer::TraceAction::CONTINUE;
}

uint64_t memoryUsage = getMemoryUsageKb() +
tracee.getSyscallArgument(1) / 1024;
memoryPeakKb_ = std::max(memoryPeakKb_, memoryUsage);
outputBuilder_->setMemoryPeak(memoryPeakKb_);
logger::debug(
"Memory usage after mmap ",
VAR(memoryUsage),
", ",
VAR(memoryPeakKb_));

if (memoryUsage > memoryLimitKb_) {
outputBuilder_->setKillReason(
printer::OutputBuilder::KillReason::MLE,
"memory limit exceeded");
logger::debug(
"Limit ",
VAR(memoryLimitKb_),
" exceeded, killing tracee");
return tracer::TraceAction::KILL;
}
return tracer::TraceAction::CONTINUE;
return handleMemoryAllocation(tracee.getSyscallArgument(1) / 1024);
}),
Arg(0) == 0 && Arg(1) > MEMORY_LIMIT_MARGIN / 2));
}
syscallRules_.emplace_back(seccomp::SeccompRule(
"mremap",
seccomp::action::ActionTrace([this](tracer::Tracee& tracee){
TRACE();
if (!vmPeakValid_) {
return tracer::TraceAction::CONTINUE;
}
bool doesUnmap = (tracee.getSyscallArgument(3)&MREMAP_DONTUNMAP)!=0;
// Allow user to shrink its memory
if(!doesUnmap&&tracee.getSyscallArgument(1)>=tracee.getSyscallArgument(2)){
return tracer::TraceAction::CONTINUE;
}
uint64_t newMemoryAllocated=tracee.getSyscallArgument(2);
// Do not count already allocated memory
if(!doesUnmap) newMemoryAllocated-=tracee.getSyscallArgument(1);
newMemoryAllocated/=1024;
return handleMemoryAllocation(newMemoryAllocated);
}),
Arg(2)>MEMORY_LIMIT_MARGIN/2));
}
tracer::TraceAction MemoryLimitListener::handleMemoryAllocation(uint64_t allocatedMemoryKb){
uint64_t memoryUsage = getMemoryUsageKb() + allocatedMemoryKb;
memoryPeakKb_ = std::max(memoryPeakKb_, memoryUsage);
outputBuilder_->setMemoryPeak(memoryPeakKb_);
logger::debug(
"Memory usage after allocation ",
VAR(memoryUsage),
", ",
VAR(memoryPeakKb_));

if (memoryUsage > memoryLimitKb_) {
outputBuilder_->setKillReason(
printer::OutputBuilder::KillReason::MLE,
"memory limit exceeded");
logger::debug(
"Limit ",
VAR(memoryLimitKb_),
" exceeded, killing tracee");
return tracer::TraceAction::KILL;
}
return tracer::TraceAction::CONTINUE;
}
void MemoryLimitListener::onPostForkChild() {
TRACE();

Expand Down
8 changes: 8 additions & 0 deletions src/limits/MemoryLimitListener.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,13 @@
#include "seccomp/policy/SyscallPolicy.h"
#include "tracer/TraceEventListener.h"

#include <sys/mman.h>

#ifndef MREMAP_DONTUNMAP
//Due to this flag being introduced in Linux 5.7 there are many system which do not define it
#define MREMAP_DONTUNMAP 4
#endif

#include <cstdint>

namespace s2j {
Expand Down Expand Up @@ -40,6 +47,7 @@ class MemoryLimitListener
pid_t childPid_;

std::vector<seccomp::SeccompRule> syscallRules_;
tracer::TraceAction handleMemoryAllocation(uint64_t allocatedMemoryKb);
};

} // namespace limits
Expand Down