vfs: skip write tracking for special files on open - #13996
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vfs: skip write tracking for special files on open#13996copybara-service[bot] wants to merge 1 commit into
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Linux skips the mount-level write check when opening a character device, block device, FIFO, or socket, so write-opening /dev/null on a read-only bind mount succeeds. gVisor was running that check unconditionally and returning EROFS, which breaks buildah's mount-bind-then-RO-remount hardening pattern when used under runsc. This adds an `IsSpecialFile` option on `FileDescription`, paired across the open and close paths so the writer counter stays balanced, and set it on every open path that backs a special-file inode. The socket and host-imported FDs live on internal disconnected mounts that are never remounted RO, so flagging them is a no-op today and exists for parity with the kernel's predicate. Fixes: #13148 FUTURE_COPYBARA_INTEGRATE_REVIEW=#13149 from shayonj:fix-special-file-rofs 87673b0 PiperOrigin-RevId: 959292441
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vfs: skip write tracking for special files on open
Linux skips the mount-level write check when opening a character device, block device, FIFO, or socket, so write-opening /dev/null on a read-only bind mount succeeds. gVisor was running that check unconditionally and returning EROFS, which breaks buildah's mount-bind-then-RO-remount hardening pattern when used under runsc.
This adds an
IsSpecialFileoption onFileDescription, paired across the open and close paths so the writer counter stays balanced, and set it on every open path that backs a special-file inode. The socket and host-imported FDs live on internal disconnected mounts that are never remounted RO, so flagging them is a no-op today and exists for parity with the kernel's predicate.Fixes: #13148
FUTURE_COPYBARA_INTEGRATE_REVIEW=#13149 from shayonj:fix-special-file-rofs 87673b0