C++: Workaround for problem with memcpy flow #2736
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The type of the source argument to `memcpy` is `void *`, and somehow
that meant that the copied object itself got type `void`. Since that has
size 0, the SSA construction did not model it as reading from the last
write.
This is probably not the right fix, but maybe it's good enough for now.
The right fix would ensure that the type reported by
`hasOperandMemoryAccess` is `UnknownType`.
When `DefaultTaintTracking.qll` is enabled, this commit has the effect
of restoring a lost results:
--- a/cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowDestination.expected
+++ b/cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowDestination.expected
@@ -1 +1,2 @@
| overflowdestination.cpp:30:2:30:8 | call to strncpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. |
+| overflowdestination.cpp:46:2:46:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. |
jbj
added a commit
to jbj/ql
that referenced
this pull request
Jan 31, 2020
As a temporary workaround in the `DefaultTaintTracking` library, we funnel flow across calls by conflating pointer and object both at the caller and the callee. The three cases in `adjustedSink` were deleted because they are now covered by the one case for `ReadSideEffectInstruction` in `instructionTaintStep`. When enabling `DefaultTaintTracking`, this commit on top of github#2736 has the effect effect of recovering two lost results: --- a/cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowDestination.expected +++ b/cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowDestination.expected @@ -1,2 +1,4 @@ | overflowdestination.cpp:30:2:30:8 | call to strncpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | | overflowdestination.cpp:46:2:46:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | +| overflowdestination.cpp:53:2:53:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | +| overflowdestination.cpp:64:2:64:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | In the internal repo, we recover one lost result. Additionally, there are two queries that gain an extra source for an existing sink. I'll classify that as noise. The new results look like this: foo(argv); // this `argv` is a new source for the sink in `bar` bar(argv); // this `argv` is the existing source for the sink in `bar`
|
I've added an IR test to demonstrate the old issue. I wouldn't be surprised if there's other weird implications of the |
|
@rdmarsh2 Your three commits LGTM. Does my original commit LGTY? |
rdmarsh2
approved these changes
Feb 3, 2020
MathiasVP
pushed a commit
to MathiasVP/ql
that referenced
this pull request
Feb 4, 2020
As a temporary workaround in the `DefaultTaintTracking` library, we funnel flow across calls by conflating pointer and object both at the caller and the callee. The three cases in `adjustedSink` were deleted because they are now covered by the one case for `ReadSideEffectInstruction` in `instructionTaintStep`. When enabling `DefaultTaintTracking`, this commit on top of github#2736 has the effect effect of recovering two lost results: --- a/cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowDestination.expected +++ b/cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowDestination.expected @@ -1,2 +1,4 @@ | overflowdestination.cpp:30:2:30:8 | call to strncpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | | overflowdestination.cpp:46:2:46:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | +| overflowdestination.cpp:53:2:53:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | +| overflowdestination.cpp:64:2:64:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | In the internal repo, we recover one lost result. Additionally, there are two queries that gain an extra source for an existing sink. I'll classify that as noise. The new results look like this: foo(argv); // this `argv` is a new source for the sink in `bar` bar(argv); // this `argv` is the existing source for the sink in `bar`
MathiasVP
pushed a commit
to MathiasVP/ql
that referenced
this pull request
Feb 4, 2020
As a temporary workaround in the `DefaultTaintTracking` library, we funnel flow across calls by conflating pointer and object both at the caller and the callee. The three cases in `adjustedSink` were deleted because they are now covered by the one case for `ReadSideEffectInstruction` in `instructionTaintStep`. When enabling `DefaultTaintTracking`, this commit on top of github#2736 has the effect effect of recovering two lost results: --- a/cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowDestination.expected +++ b/cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowDestination.expected @@ -1,2 +1,4 @@ | overflowdestination.cpp:30:2:30:8 | call to strncpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | | overflowdestination.cpp:46:2:46:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | +| overflowdestination.cpp:53:2:53:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | +| overflowdestination.cpp:64:2:64:7 | call to memcpy | To avoid overflow, this operation should be bounded by destination-buffer size, not source-buffer size. | In the internal repo, we recover one lost result. Additionally, there are two queries that gain an extra source for an existing sink. I'll classify that as noise. The new results look like this: foo(argv); // this `argv` is a new source for the sink in `bar` bar(argv); // this `argv` is the existing source for the sink in `bar`
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The type of the source argument to
memcpyisvoid *, and somehow that meant that the copied object itself got typevoid. Since that has size 0, the SSA construction did not model it as reading from the last write.This is probably not the right fix, but maybe it's good enough for now. The right fix would ensure that the type reported by
hasOperandMemoryAccessisUnknownType.When
DefaultTaintTracking.qllis enabled, this commit has the effect of restoring a lost results: