wasmparser: Relocation range end can wrap on 32-bit targets#2497
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dicej merged 2 commits intobytecodealliance:mainfrom Apr 17, 2026
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RelocationEntry::relocation_range() derived a Range<usize> from untrusted relocation offsets using `self.offset as usize` and start + self.ty.extent(). On 32-bit targets, large parsed offsets can overflow the end computation, causing a debug-build panic or release-build wraparound instead of rejection. That can be reproduced with a 30-byte wasm module consisting of a header and a single `reloc.CODE` custom section with one entry: | Field | Value | Encoding | |--------|---------------------------|--------------------------------| | type | `FunctionIndexLeb` (0x00) | extent = 5, no addend | | offset | `0xFFFF_FFFC` | LEB128: `FC FF FF FF 0F` | | index | 0 | LEB128: `00` | $ cargo build -p wasmparser --example reloc_overflow --target wasm32-wasip1 $ wasmtime target/wasm32-wasip1/debug/examples/reloc_overflow.wasm parsed: type=FunctionIndexLeb, offset=0xFFFFFFFC, extent=5 thread 'main' panicked at crates/wasmparser/src/readers/core/reloc.rs:246:33: attempt to add with overflow In release mode the panic becomes a silent wraparound: $ cargo build --release -p wasmparser --example reloc_overflow --target wasm32-wasip1 $ wasmtime target/wasm32-wasip1/release/examples/reloc_overflow.wasm parsed: type=FunctionIndexLeb, offset=0xFFFFFFFC, extent=5 relocation_range() = 0xFFFFFFFC..0x1 BUG: range end < start due to overflow Autonomously found by https://swival.dev /scan
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RelocationEntry::relocation_range() derived a Range from untrusted relocation offsets using
self.offset as usizeand start + self.ty.extent().On 32-bit targets, large parsed offsets can overflow the end computation, causing a debug-build panic or release-build wraparound instead of rejection.
That can be reproduced with a 30-byte wasm module consisting of a header and a single
reloc.CODEcustom section with one entry:FunctionIndexLeb(0x00)0xFFFF_FFFCFC FF FF FF 0F00$ cargo build -p wasmparser --example reloc_overflow --target wasm32-wasip1 $ wasmtime target/wasm32-wasip1/debug/examples/reloc_overflow.wasm
parsed: type=FunctionIndexLeb, offset=0xFFFFFFFC, extent=5
thread 'main' panicked at crates/wasmparser/src/readers/core/reloc.rs:246:33: attempt to add with overflow
In release mode the panic becomes a silent wraparound:
$ cargo build --release -p wasmparser --example reloc_overflow --target wasm32-wasip1 $ wasmtime target/wasm32-wasip1/release/examples/reloc_overflow.wasm
parsed: type=FunctionIndexLeb, offset=0xFFFFFFFC, extent=5 relocation_range() = 0xFFFFFFFC..0x1
BUG: range end < start due to overflow
Autonomously found by https://swival.dev /scan