squashfs: handle images with no fragment or xattr table#413
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squashfs-tools-ng writes valid images that omit the fragment table (e.g. a single empty directory, or with -no-tail-packing) and/or the xattr table (the NO_XATTRS superblock flag). The reader mishandled both: - readFragmentTable read the table even when fragmentCount == 0. In that case fragmentTableStart holds the 0xffff... "not present" sentinel, so the ReadAt seeks to offset -1 and fails with "invalid seek position". - directoryEntryFromInode dereferenced fs.xattrs when an inode advertised an xattr index while the image had no xattr table (fs.xattrs == nil), causing a nil-pointer panic in (*xAttrTable).find. Guard both: return early for an absent fragment table, and skip the xattr lookup when the table is nil. Adds regression tests for both paths. Surfaced via rclone (rclone/rclone#9004), which uses this reader for its archive backend; both a single-empty-dir image and a real squashfs-tools-ng image now list correctly. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Signed-off-by: maximilize <max@maxmax.ch>
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Problem
The squashfs reader fails on valid images written by squashfs-tools-ng that omit optional tables. Two independent failures, both reproducible with a minimal image (
gensquashfs -D <empty-dir> out.sqfs):fragmentCount == 0):readFragmentTablereads unconditionally, butfragmentTableStartholds the0xffffffffffffffff"not present" sentinel, soReadAtseeks to offset-1and fails witherror reading fragment table index: invalid seek position.NO_XATTRSflag):directoryEntryFromInodecallsfs.xattrs.find(...)when an inode advertises an xattr index, butfs.xattrsisnil, causing a nil-pointer panic in(*xAttrTable).find(xattr.go:46).Fix
Two guards, mirroring the "absent optional table" handling already done when the superblock is parsed (
!s.noXattrs && s.xattrTableStart != 0xffffffffffffffff):fragmentCount == 0;fs.xattrs == nil.Tests
Added two internal regression tests (
TestReadFragmentTableNoFragmentsandTestDirectoryEntryFromInodeNilXattrTable), both failing before / passing after. Fullfilesystem/squashfssuite passes andgo vetis clean.Verified end-to-end through rclone's
archivebackend (which uses this reader): the two images from rclone/rclone#9004 that previously errored / panicked (a single empty directory, and a real squashfs-tools-ng Windows image) now list correctly.