fix: reject symlinks with sysopen O_EXCL|O_CREAT per POSIX#376
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fix: reject symlinks with sysopen O_EXCL|O_CREAT per POSIX#376toddr-bot wants to merge 1 commit intocpan-authors:mainfrom
toddr-bot wants to merge 1 commit intocpan-authors:mainfrom
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POSIX open(2) mandates that O_EXCL|O_CREAT must fail with EEXIST when the final path component is a symbolic link, regardless of where it points. This is a security feature to prevent symlink race attacks (TOCTOU). Previously, sysopen with O_EXCL|O_CREAT would follow symlinks and only check whether the resolved target existed, allowing exclusive-create through a symlink — violating POSIX semantics. Add a pre-resolution check: when both O_EXCL and O_CREAT are set, inspect the path directly (without following) and fail immediately if it is a symlink. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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What
sysopen() with O_EXCL|O_CREAT now fails with EEXIST when the path is a symbolic link, matching POSIX open(2) semantics.
Why
POSIX mandates this behavior as a security measure against symlink race attacks (TOCTOU). Previously, O_EXCL|O_CREAT would follow the symlink and only check whether the resolved target existed — allowing exclusive-create through a symlink, which defeats the purpose of O_EXCL.
How
Added a pre-resolution check in
__sysopen: before following symlinks, if both O_EXCL and O_CREAT are set, inspect the path directly via_get_file_object(). If it's a symlink, return EEXIST immediately.Testing
7 new tests in
t/sysopen.tcovering:Full test suite passes (pre-existing
fh-ref-leak.tfailure is an upstream Overload::FileCheck version issue, unrelated).🤖 Generated with Claude Code
Quality Report
Changes: 2 files changed, 54 insertions(+)
Code scan: clean
Tests: failed (4 Failed, 94 test)
Branch hygiene: clean
Generated by Kōan post-mission quality pipeline