read/macho: bound exports trie traversal to avoid exponential blowup#953
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scadastrangelove wants to merge 1 commit into
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read/macho: bound exports trie traversal to avoid exponential blowup#953scadastrangelove wants to merge 1 commit into
scadastrangelove wants to merge 1 commit into
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The cycle check added in gimli-rs#940 rejects a child offset equal to an ancestor, but not shared subtrees: a node reached by multiple non-ancestor paths is re-traversed each time. A small crafted trie whose every node has two edges to the same next node has 2^depth root-to-leaf paths, so the DFS runs in exponential time (a ~330-byte Mach-O hangs the exports_trie iterator). A well-formed exports trie is a prefix tree with at most data.len() nodes, so a valid DFS needs at most ~2 * data.len() steps. Bound the traversal to that and stop cleanly when exceeded, which covers shared-subtree (and any residual cyclic) inputs. Verified: cargo test passes (lib incl exports_trie + integration), valid tries still traverse, and the crafted exponential trie now terminates. Discovered by the rust-in-peace security pipeline (https://github.com/scadastrangelove/rust-in-peace/).
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Fixes #952.
The cycle check added in #940 rejects a child offset equal to an ancestor, but not shared subtrees: a node reached by multiple non-ancestor paths is re-traversed each time. A trie whose every node has two edges to the same next node therefore has
2^depthroot-to-leaf paths and the DFS runs in exponential time (a ~330-byte Mach-O hangs theexports_trie()iterator).A well-formed exports trie is a prefix tree with at most
data.len()nodes, so a valid DFS needs at most ~2 * data.len()steps. This bounds the traversal to that and stops cleanly when exceeded, covering shared-subtree (and any residual cyclic) inputs.Verified against
main:cargo testpasses (25 lib incl theexports_trietests, integration, and--features all), valid tries still traverse, and the crafted exponential trie (#952) now terminates instead of hanging.Discovered by the rust-in-peace security pipeline.