bcachefs: guard dirent to_text against unvalidated names - #1202
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bcachefs: guard dirent to_text against unvalidated names#1202matthiasgoergens wants to merge 2 commits into
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bch2_dirent_to_text() may be called on unvalidated keys: the sb validation error path prints a corrupt clean section's journal entries, and a dirent key with a truncated value or an inflated name length reached the printer, which then read past the key in prt_bytes(). Return early with an invalid marker when the key header is truncated (bkey_val_u64s() underflows when u64s < BKEY_U64s, so the header length is checked explicitly) or the value is smaller than struct bch_dirent, and check the name and lookup-name extents against the value bounds before printing. The extent guards check the length against the value size before computing the sum: qstr.len is u32 and bch2_dirent_name_bytes() can underflow to 0xffffffff, so the sum would wrap in 32-bit arithmetic. The guards bound extents against the key's declared u64s; the callers' walkers bound the declared extent to actual storage. Found by fuzzing the offline tools with AFL++/ASAN.
This was referenced Aug 17, 2026
Tests the truncated-key, underflowed-name, and casefold overrun paths, all of which previously crashed.
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bch2_dirent_to_text() may be called on unvalidated keys: the sb
validation error path prints a corrupt clean section's journal entries,
and a dirent key with a truncated value or an inflated name length read
past the key in prt_bytes().
Return early with an invalid marker for truncated keys, and check the
name and lookup-name extents against the value bounds before printing.
The extent guards check the length before computing the sum, so the sum
cannot wrap (qstr.len is u32 and bch2_dirent_name_bytes() can underflow).
Adds kunit tests for the truncated, underflowed-name, and casefold
overrun paths, passing under UML.
Found by fuzzing the offline tools with AFL++/ASAN.
The bcachefs-tools tree has the same fix in
koverstreet/bcachefs-tools#877.