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AT_SYMLINK_NOFOLLOW must only suppress following the final pathname component. do_utimensat previously used lookup(), whose zero symlink budget also prevented intermediate directory symlinks from being resolved. Valid usr-merged paths consequently failed with ENOTDIR. Reuse lookup_follow_symlink2 with the normal follow budget and an explicit final-component policy. Keep the fd path, timestamp permission checks, metadata masks and notification behavior unchanged. This fixes the trigger observed while Ubuntu dpkg sets timestamps on /sbin/ip.dpkg-new during iproute2 installation. The prior error entered dpkg's diversion cleanup path, which removed /bin and /sbin and prevented the next boot. The kernel change does not special-case those names or claim to fix dpkg's independent rollback behavior. Add 30 parameterized dunitest checks covering tmp and current-directory fixtures, intermediate relative/absolute links, dirfd paths, final and dangling links, trailing slashes, search permissions, error cases, UTIME_OMIT, current-time updates and futimens. Register the suite in the CI whitelist and no-skip list. Validation: - Linux new suite: 30 passed; pre-fix DragonOS: 6 passed, 24 failed. - Fixed DragonOS on tmpfs/ext4: 30 passed, including after reboot. - Existing open_dangling_symlink suite: 11 passed. - Selected gVisor utimes/futimesat/utimensat tests: 14 passed. - make kernel, make fmt and FMT_CHECK=1 make fmt passed. - Normal nginx apt installation completed with iproute2, nginx-common and nginx installed; system links survived sync and reboot. The separate nginx dual-stack bind failure remains outside this fix. Signed-off-by: longjin <longjin@dragonos.org>
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Summary
utimensat(AT_SYMLINK_NOFOLLOW)to follow intermediate directory symlinks while leaving the final symlink unfollowed.Root cause
The pathname branch used
lookup(), which disables all symlink traversal, instead of selecting only the final-component policy. A valid path such as/sbin/ip.dpkg-newtherefore returnedENOTDIRon a usr-merged Ubuntu rootfs.This was reproduced without nginx by unpacking Ubuntu iproute2 6.1.0-1ubuntu6.4. dpkg 1.22.6ubuntu6.6 then entered its diversion rollback path: extraction used the diverted directory names, while cleanup used the original names and removed
/binand/sbin. The next boot could not resolve/bin/busybox.This PR fixes the kernel trigger by matching Linux 6.6 pathname semantics. It does not add path-specific unlink protection or modify dpkg, and does not claim to fix dpkg rollback under unrelated installation errors.
Validation
make kernelmake fmtFMT_CHECK=1 make fmtnginx -tThe gVisor selection excludes the existing blocklisted
UtimeTest.ZeroAtimeandMtime; no reference tests or blocklists were changed. Independent adversarial reviews covered Linux semantics, permissions, lifecycle, performance, maintainability and test validity.Scope and remaining issues
Default nginx service startup still reports
EADDRINUSEfor[::]:80; a separate IPv4 smoke test succeeds. This networking issue, the previously observed concurrency/TLS issues, and dpkg's independent diversion rollback risk are not fixed by this PR. Installation and reboot success must not be interpreted as full nginx compatibility.