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fix(redact-prepush): close the remaining shapes of three fail-open classes

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Three shapes still exited 0 with a credential in the push.

A push to a URL borrowed origin's tip as its base and excluded every commit
any remote had seen, so a credential already on origin shipped to a new,
empty URL remote unscanned. A URL is described by no remote-tracking ref:
the push target is now a three-way value (configured remote / URL /
unknown), a URL target anchors on nothing and excludes nothing, and an
unknown target keeps the historical origin-shaped behavior.

When git named a remote tip the local clone lacks, only an EMPTY guessed
range was blocked; a stale tracking ref holding the credential plus one
harmless local commit produced a non-empty, credential-free guess that
passed. An absent named tip now gets no local narrowing at all and the
whole reachable history is scanned, which is affordable because every scan
is sliced under the engine's cap.

The inter-slice overlap carried whole lines only, so a line longer than
the overlap contributed nothing and a label at its end never met the secret
at the start of the next slice. The overlap now carries such a line's
suffix.

Gate: test/redact-prepush-fail-open.sh grows to 30 scenarios. E5 expected
the URL-push leak to be ALLOWED and now expects the block, E5b pins that a
clean URL push is still allowed, 19 and 20 pin the other two shapes, and
E8b pins that a clean SHA-256 first push is allowed (E8 carried a
credential, so it could not tell a working empty-tree fix from a broken
one). The S1 URL-push case in redact-prepush-scan-range.test.ts keeps its
no-error assertion and now also asserts the block, because its fixture's
secret really is delivered to that URL.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Lubos Buracinsky
2026-09-22 18:09:53 +02:00
co-authored by Claude Opus 5
parent 11734707df
commit 9c15f7bf45
3 changed files with 215 additions and 36 deletions
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test/redact-prepush-fail-open.sh
+86 -4
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@@ -249,7 +249,10 @@ run_missingremote() { cd "$1" || exit 1; local sha; sha=$(git rev-parse HEAD)
printf 'refs/heads/main %s refs/heads/main cafebabecafebabecafebabecafebabecafebabe\n' "$sha" \
| bun "$CAND" origin https://example.invalid/origin.git 2>&1; echo "___EXIT:$?"; }
S16=$(run_missingremote "$R/s12")
row "16 missing-but-shaped remote sha" "$S16" "BLOCK(unscannable)"
# Now that an absent named tip drops ALL local narrowing, this blocks with the
# actual finding rather than an "unscannable" apology: the whole reachable
# range is scanned and the credential is named.
row "16 missing-but-shaped remote sha" "$S16" "BLOCK(aws.access_key)"
# 17: zero-width across slice boundary
mkrepo s17; SEC="${_S1}${_S2}" python3 -c "
@@ -280,6 +283,31 @@ git add -A >/dev/null; git commit -qm proxsplit
S18=$(run_probe "$R/s18")
row "18 proximity split by slice cut" "$S18" "BLOCK(aws.secret_key)"
# 20: an absent named tip whose GUESS is non-empty but wrong.
# Row 16 covers the absent-tip case where the guess scans nothing. This is the
# other half: the stale tracking ref holds the credential, one harmless local
# commit sits on top, so the guessed range is non-empty and credential-free.
# Blocking only the empty guess let this through with exit 0.
mkrepo s20
printf 'aws_access_key_id = %s\n' "$KEY" > secret.txt
git add -A >/dev/null
git commit -qm cred >/dev/null
git update-ref refs/remotes/origin/main HEAD
git remote add origin https://example.invalid/o.git
git remote set-head origin main >/dev/null 2>&1
echo 'harmless = 1' > ok.py
git add -A >/dev/null
git commit -qm harmless >/dev/null
run_absent_tip() {
cd "$1" || exit 1
local sha
sha=$(git rev-parse HEAD)
printf 'refs/heads/main %s refs/heads/main aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa7\n' "$sha" \
| bun "$CAND" origin https://example.invalid/o.git 2>&1
echo "___EXIT:$?"
}
S20=$(run_absent_tip "$R/s20")
row "20 absent named tip, non-empty wrong guess" "$S20" "BLOCK(aws.access_key)"
# E1: ordinary new-branch push must scan ONLY the new commit
mkrepo e1
printf 'aws_key = "%s"\n' "$KEY" > old.py
@@ -324,7 +352,11 @@ E4=$(cd "$R/e4" && printf 'refs/heads/main %s refs/heads/main %s\n' "$ZERO40" "$
| bun "$CAND" origin https://example.invalid/o.git 2>&1; echo "___EXIT:$?")
row "E4 branch delete skipped" "$E4" "ALLOW"
# E5: URL push keeps historical origin-shaped fallback
# E5: a URL push must NOT borrow origin's tip as its base.
# The credential is already on origin/main and the local commit adds only
# harmless content. Anchoring on origin (or excluding origin's commits as
# "already pushed") scans the harmless commit only and ships the credential to
# a remote that never had it. A URL target is described by no tracking ref.
mkrepo e5
printf 'aws_key = "%s"\n' "$KEY" > old.py
git add -A >/dev/null; git commit -qm old >/dev/null
@@ -334,7 +366,36 @@ git checkout -q -b feature
echo 'harmless = 1' > new.py; git add -A >/dev/null; git commit -qm new >/dev/null
E5=$(cd "$R/e5" && printf 'refs/heads/main %s refs/heads/main %s\n' "$(git rev-parse HEAD)" "$ZERO40" \
| bun "$CAND" https://example.invalid/direct.git '' 2>&1; echo "___EXIT:$?")
row "E5 URL push falls back to origin (narrow)" "$E5" "ALLOW"
row "E5 URL push does not borrow origin's base" "$E5" "BLOCK(aws.access_key)"
# E5b: the other half of E5 — over-scanning must not turn every URL push into a
# block. Same shape, no credential anywhere: the push has to be allowed.
mkrepo e5b
echo 'old = 1' > old.py
git add -A >/dev/null; git commit -qm old >/dev/null
git update-ref refs/remotes/origin/main HEAD
git remote add origin https://example.invalid/o.git
git checkout -q -b feature
echo 'harmless = 1' > new.py; git add -A >/dev/null; git commit -qm new >/dev/null
E5B=$(cd "$R/e5b" && printf 'refs/heads/main %s refs/heads/main %s\n' "$(git rev-parse HEAD)" "$ZERO40" \
| bun "$CAND" https://example.invalid/direct.git '' 2>&1; echo "___EXIT:$?")
row "E5b clean URL push still allowed" "$E5B" "ALLOW"
# 19: a line longer than the overlap must still contribute its END to the seam.
# One ~770 KB ASCII line whose tail is the qualifying label, then a line holding
# the secret. Carrying whole lines only leaves the seam with no context, so
# aws.secret_key never fires even though both halves are in the pushed diff.
mkrepo s19
SEC="$SEC" python3 -c "
import os
sec=os.environ['SEC']
filler='x'*770047
with open('big.txt','w') as f:
f.write(filler+' aws_secret_access_key =\n')
f.write(sec+' '+'y'*20000+'\n')"
git add -A >/dev/null; git commit -qm bigline >/dev/null
S19=$(run_probe "$R/s19")
row "19 label at the end of an over-overlap line" "$S19" "BLOCK(aws.secret_key)"
# E6: long-line slicer survives multi-byte text
mkrepo e6; KEY="$KEY" python3 -c "
@@ -370,7 +431,28 @@ if git init -q --object-format=sha256 "$R/.probe256" 2>/dev/null; then
ZERO64=$(printf '0%.0s' {1..64})
E8=$(cd "$d" && printf 'refs/heads/main %s refs/heads/main %s\n' "$(git rev-parse HEAD)" "$ZERO64" \
| bun "$CAND" origin https://example.invalid/o.git 2>&1; echo "___EXIT:$?")
row "E8 sha256 repo, new branch" "$E8" "BLOCK"
row "E8 sha256 repo, new branch" "$E8" "BLOCK(aws.access_key)"
# E8b: the row that actually proves the empty-tree OID fix. E8 alone does not:
# it carries a credential, so a build that cannot resolve the fallback range
# still "blocks", just with a diff error instead of a finding. A CLEAN sha256
# first push must be ALLOWED — under the hardcoded SHA-1 empty-tree OID it was
# hard-blocked, which is unusable rather than safe.
d="$R/e8b"
rm -rf "$d"
mkdir -p "$d"
cd "$d" || exit 1
git init -q --object-format=sha256 .
git config user.email t@t.t
git config user.name t
git checkout -q -b main
printf 'cfg = 1\nharmless = 2\n' > app.py
git add -A >/dev/null
git commit -qm seed >/dev/null
git remote add origin https://example.invalid/o.git
E8B=$(printf 'refs/heads/main %s refs/heads/main %s\n' "$(git rev-parse HEAD)" "$ZERO64" \
| bun "$CAND" origin https://example.invalid/o.git 2>&1; echo "___EXIT:$?")
row "E8b clean sha256 first push allowed" "$E8B" "ALLOW"
fi
echo