verify() asked Cache::has(), verified, then Cache::put(). Between the read
and the write the key is free, so two requests carrying the same code
could both be told yes -- which is exactly what the replay guard exists to
prevent, and the window an intercepted code has is the whole of its
validity either side.
The claim is now the answer: Cache::add() writes only if the key is
absent, so of two requests carrying the same valid code exactly one gets
true back. That is the same mechanism, for the same reason, as the
preview log's debounce -- "Cache::add is the whole mechanism: it writes
only if the key is absent ... without a read-then-write race between two
of them".
Verification still happens first, so a wrong code never touches the cache
and cannot burn the window for the code the person is about to type
correctly.
One test, modelling the interleaving it is about: the winner's claim has
landed, and the loser's has() answers from before that write. Without the
fix the loser is signed in.
consumeRecoveryCode() reads the whole list, filters the used code out,
and writes the whole list back. Two requests that both read before
either writes each store their own copy, and the second write puts back
the code the first removed. So a spent code comes back, and the same
code offered twice is accepted twice -- while the method's first line
says "each code works exactly once".
Nobody gets in through this who was not already holding a valid code, so
it is a promise not being kept rather than a door standing open. The
promise is worth keeping anyway: it is the whole reason a printed sheet
of recovery codes can be crossed off, and it is what makes a code that
somebody watched being typed in stop working.
The decision now comes from the row as it stands, re-read under a lock
inside the transaction that writes it -- the shape SendNotificationDigest
already uses to claim the rows it is about to delete. A conditional
update, as in PublicShareController's downloads_count and the delivered_at
claim in #1692, is the other precedent in the tree, but the column is
`encrypted:array`: there is nothing in it a database can compare, so the
comparison has to happen after decryption, under something that holds the
row while it does.
The lock is what makes it atomic against a request arriving at the same
moment. The re-read is what makes the decision right, and it is the half
a test can show: SQLite ignores lockForUpdate, so the accompanying tests
pin the re-read and say so rather than claiming to prove the locking.
config/database.php runs MySQL or Postgres in production, and both honour
it. Saving through the caller's own instance keeps that instance in step
with the row, so a caller cannot go on to decide from a list the database
no longer has.
Client file sharing, rebuilt from the ground up: a private area per
client, resumable uploads, folders, groups and categories, sharing with
expiry dates and download limits, comments, file versions, an activity
log, a REST API, and sixteen languages.
This repository begins here. ProjectSend 2 was developed privately, and
that development history is not published — the previous generation
remains available, with its own history, at projectsend/legacy.
Free software under the GNU General Public License v2, or (at your
option) any later version.
denkfabrik-li