fix: use umask(0177) before bind to prevent S_IXUSR race#12
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DonaldoDes wants to merge 1 commit intomobydeck:mainfrom
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fix: use umask(0177) before bind to prevent S_IXUSR race#12DonaldoDes wants to merge 1 commit intomobydeck:mainfrom
DonaldoDes wants to merge 1 commit intomobydeck:mainfrom
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create_socket restored the original umask before calling bind(2).
With a typical shell umask of 022, bind created the socket file with
mode 0755 (S_IXUSR set). chmod(0600) was called right after, but the
tiny window between bind and chmod was enough for a concurrent
`atch list` to see the stale execute bit and report a freshly started
session as [attached] — even though no client had ever connected.
The fix switches to umask(0177) before bind so the kernel creates the
socket file directly at mode 0600 (0777 & ~0177). S_IXUSR is never
present on the socket path during creation, closing the TOCTOU window
entirely. The subsequent chmod(0600) is kept for explicitness and to
guard against any platform-specific deviations.
Adds regression test 24 (start-inside-session) that:
- starts an outer session and attaches a python client to it
- starts an inner session with ATCH_SESSION set (simulating being
inside the outer session)
- asserts the inner session socket has no execute bit immediately
after creation
- asserts `atch list` does not show the inner session as [attached]
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
umask(0177)beforebind()increate_socket()so the socket file is created directly with mode0600atch listcould read staleS_IXUSRbetweenbind()andchmod()bind()Closes #8
Test plan
atch start(no S_IXUSR window)atch listnever shows[attached]for freshly started sessions🤖 Generated with Claude Code