https://bugs.llvm.org/show_bug.cgi?id=47475
Bug ID: 47475
Summary: [coroutines] Destroying a coroutine inside
await_suspend with symmetric-transfer form hits asan
use-after-free in non-optimized builds
Product: clang
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangb...@nondot.org
Reporter: lewissba...@gmail.com
CC: llvm-bugs@lists.llvm.org, neeil...@live.com,
richard-l...@metafoo.co.uk
See https://godbolt.org/z/G7xM8G
The problem seems to be with the code generated for symmetric-transfer style
suspend-points (where await_suspend() returns a coroutine_handle to be
resumed).
Under non-optimised builds the compiler generates code that materializes the
returned coroutine_handle as a temporary in before then calling
__builtin_coro_resume() on its address. However, it materializes the
coroutine_handle using storage from the coroutine-frame rather than
materializing it on the stack.
For coroutines that destroy themselves inside await_suspend(), this results in
a use-after-free, as the compiler is trying to write the materialized
coroutine_handle to the now-freed coroutine frame upon return of
await_suspend().
It should instead be materializing the returned coroutine_handle on the stack.
This is unlikely to be an issue under optimised builds as the returned
coroutine_handle is generally kept in a register.
This seems to have been an issue since Clang 7, when symmetric-transfer was
first introduced.
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