Fix a panic with an invalid name section #3509
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This commit fixes a panic which can happen on a module with an invalid name section where one of the functions named has the index `u32::MAX`. Previously Wasmtime would create a new `FuncIndex` with the indices found in the name section but the sentinel `u32::MAX` causes a panic. Cranelift otherwise limits the number of functions through `wasmparser` which has a hard limit (lower than `u32::MAX`) so this commit applies a fix of only recording function names for function indices that are actually present in the module.
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@alexcrichton: do you know if this bug has any security impact? |
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@ulan this means that if arbitrary input is fed into |
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Thanks @alexcrichton. Sorry, I forgot to mention that in a test that I tired the panic happens only in the debug mode. Could it be that the assertion is enabled only in debug mode? If so, could the bug lead to something exploitable in release mode? In any case, do you think it is worthwhile to merge the fix back in the last two released versions? |
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Oh right sorry now I remember what I thought when I was originally thinking about this. Indeed yeah this is a debug assert so the assert doesn't happen in release mode, which means my previous comment is not actually correct because most embeddings are built in release mode. I remember now though that my conclusion was that this would cause no issues. Nothing bad will happen for bad name section indices in reality and this was mostly just a debug check we needed to fixup. In that sense no need for security backports or anything. |
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Happy to hear that! Thanks @alexcrichton. |
alexcrichton
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Move these up to Wasmtime's misc testsuite to get translated and instantiated by Wasmtime. Note that the max-function-index-in-name-section test was removed here as that's tested by the support added in bytecodealliance#3509.
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* Move remaining `*.wat` tests out of cranelift-wasm/wasmtests Move these up to Wasmtime's misc testsuite to get translated and instantiated by Wasmtime. Note that the max-function-index-in-name-section test was removed here as that's tested by the support added in #3509. * Remove cranelift-wasm test for name section This is pretty thoroughly tested elsewhere in Wasmtime that we respect the name section, for example many of the trap tests assert that the name of the function comes from the text format. * Move reachability tests out of cranelift-wasm Instead add them to the disassembly test suite to ensure we don't generate dead code. Additionally this has a lot of coverage via fuzzing too. * Move more tests out of cranelift-wasm Move them into `tests/disas` so we can easily see the CLIF.
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The cranelift/wasm/wasmtests suite verifies that the given WebAssembly modules compile without errors using cranelift-wasm's DummyEnvironment. That environment is not particularly representative of how we actually compile WebAssembly modules in Wasmtime, so it's better to perform these tests in Wasmtime itself. The rust_fannkuch test can move to Wasmtime's misc test suite because it can be both compiled and instantiated without any extra setup. This tests more than was tested in cranelift-wasm, which didn't try to instantiate the module. By moving it to a wast test we could also choose to add assertions about the execution of this module, but I don't think that's necessary. I'm just deleting the embenchen tests because they can't be instantiated without setting up a bunch of imports, and it's not clear to me that testing that they can be compiled offers any value for helping us find bugs or regressions. Finally, I'm also deleting the test case which was extracted from a fuzz bug in 2019, before Cranelift was merged into the Wasmtime repo: bytecodealliance/cranelift#1306 That test is interesting, but running it here only tests code in DummyEnvironment, not anything reachable from Wasmtime. There was a report of exactly the same bug in Wasmtime two years later, and the fix included tests in tests/misc_testsuite/empty.wast to cover this case. bytecodealliance#3509 The `empty.wast` test is better than this one because it has minimal and well-commented binary modules which I've verified still trigger the same bug if the fix is reverted. By contrast, since this older test was produced by a fuzzer, it is larger than necessary and the end of its name section is malformed and unparseable.
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This commit fixes a panic which can happen on a module with an invalid
name section where one of the functions named has the index
u32::MAX.Previously Wasmtime would create a new
FuncIndexwith the indicesfound in the name section but the sentinel
u32::MAXcauses a panic.Cranelift otherwise limits the number of functions through
wasmparserwhich has a hard limit (lower than
u32::MAX) so this commit applies afix of only recording function names for function indices that are
actually present in the module.