From a56f5c0dc2287a4ff456e577f8aadc2988241eed Mon Sep 17 00:00:00 2001
From: hugocasa <hugo@casademont.ch>
Date: Mon, 17 Aug 2026 19:29:52 +0200
Subject: [PATCH] fix(agents): keep redirects and chained writes off the allow
 path

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 .claude/hooks/allow-fileops-in-tmp.sh | 18 +++++++++++++-----
 .claude/hooks/guard-rm-outside-tmp.sh |  3 +++
 .claude/hooks/test-hooks.sh           |  9 +++++++--
 3 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/.claude/hooks/allow-fileops-in-tmp.sh b/.claude/hooks/allow-fileops-in-tmp.sh
index 71800a9313..62dbbe18ad 100755
--- a/.claude/hooks/allow-fileops-in-tmp.sh
+++ b/.claude/hooks/allow-fileops-in-tmp.sh
@@ -238,7 +238,7 @@ split_segments "$cmd"
 seg_cwd="${cwd:-$PWD}"
 alt_cwd=""                                # where a `cd` that failed would have left the command
 saw_cd=0                                  # a `cd` moved the working directory somewhere
-proved=0                                  # at least one op came out inside a single root
+proved=0                                  # how many ops came out inside a single root
 only_ours=1                               # ... and nothing else shares the command line
 
 for seg in "${SEGMENTS[@]}"; do
@@ -247,12 +247,12 @@ for seg in "${SEGMENTS[@]}"; do
     "") continue ;;
     mkdir | cp | mv | touch | chmod)
       check_fileops_segment "${SEG_TOKS[0]}"
-      proved=1
+      proved=$((proved + 1))
       continue
       ;;
     tar | unzip)
       check_archive_segment "${SEG_TOKS[0]}"
-      proved=1
+      proved=$((proved + 1))
       continue
       ;;
     cd)
@@ -265,7 +265,10 @@ for seg in "${SEGMENTS[@]}"; do
         alt_cwd="$seg_cwd"
         seg_cwd="$new_cwd"
       else
+        # Not the harmless segment an allow assumes: whatever this guard could not account for
+        # may be a redirect, and a redirect writes. Leave the line to the normal flow.
         seg_cwd="" alt_cwd=""
+        only_ours=0
       fi
       saw_cd=1
       continue
@@ -279,6 +282,11 @@ for seg in "${SEGMENTS[@]}"; do
   only_ours=0
 done
 
-[ "$proved" = 1 ] || exit 0
-[ "$only_ours" = 1 ] && decide allow "every path operand is under /tmp"
+# Exactly one write per line. Each segment is proved against the filesystem as it stands now,
+# and an earlier write can change what a later operand means: `cp -r /tmp/tree /tmp/live` that
+# recreates a symlink out of /tmp turns `/tmp/live/link` — a path under /tmp when this ran —
+# into a write through that symlink. Deletes compose safely and guard-rm-outside-tmp.sh allows
+# several, because `rm` unlinks a symlink rather than following it.
+[ "$proved" -ge 1 ] || exit 0
+[ "$only_ours" = 1 ] && [ "$proved" = 1 ] && decide allow "every path operand is inside a single root"
 exit 0
diff --git a/.claude/hooks/guard-rm-outside-tmp.sh b/.claude/hooks/guard-rm-outside-tmp.sh
index 453d010147..7c352dd3a7 100755
--- a/.claude/hooks/guard-rm-outside-tmp.sh
+++ b/.claude/hooks/guard-rm-outside-tmp.sh
@@ -122,7 +122,10 @@ for seg in "${SEGMENTS[@]}"; do
         alt_cwd="$seg_cwd"
         seg_cwd="$new_cwd"
       else
+        # Not the harmless segment an allow assumes: whatever this guard could not account for
+        # may be a redirect, and a redirect writes. Leave the line to the normal flow.
         seg_cwd="" alt_cwd=""
+        only_ours=0
       fi
       saw_cd=1
       continue
diff --git a/.claude/hooks/test-hooks.sh b/.claude/hooks/test-hooks.sh
index 2e4f0d8dd6..d2ad4378c1 100644
--- a/.claude/hooks/test-hooks.sh
+++ b/.claude/hooks/test-hooks.sh
@@ -131,6 +131,7 @@ run $G ask   "cd /tmp/does-not-exist; rm -rf backend/.env"
 run $G ask   "cd /tmp/a && cd /tmp/b && rm -rf sub"
 run $G ask   "rm -rf /tmp/clone/.git"                     # history is never in a class
 run $G ask   "rm -rf /tmp/scratch/id_rsa.key"
+run $G none  "cd /tmp >$OUT; rm -f /tmp/a"
 
 echo
 echo "== allow-fileops-in-tmp.sh =="
@@ -154,8 +155,8 @@ run $A none  "cp $CWD/AGENTS.md /tmp/a"
 run $A none  "tar -xzf /tmp/a.tar.gz -C $OUT"
 run $A none  "cargo build"
 
-run $A allow "mkdir -p /tmp/x; mv /tmp/a /tmp/x; chmod 755 /tmp/x"
-run $A allow "$(printf 'mv /tmp/a /tmp/b\nchmod 755 /tmp/b')"
+run $A none  "mkdir -p /tmp/x; mv /tmp/a /tmp/x; chmod 755 /tmp/x"   # one write per line
+run $A none  "$(printf 'mv /tmp/a /tmp/b\nchmod 755 /tmp/b')"
 run $A ask   "ls && mv /tmp/a /etc"
 run $A ask   "$(printf 'mkdir -p /tmp/x\nchmod -R 777 %s' "$CWD")"
 run $A allow "cd /tmp/x && tar -xzf /tmp/a.tar.gz -C /tmp/out"
@@ -175,6 +176,10 @@ run $A none  "cp backend/secrets/token frontend/token.txt"   # cp has no prompt
                                                             # so what matters is it is not allowed
 run $A ask   "mv $CWD/backend/credentials.json /tmp/x"
 run $A ask   "cd /tmp/does-not-exist; mv .claude/settings.json settings.bak"
+# A segment this hook cannot read whole may carry a redirect, and an earlier write can change
+# what a later operand resolves to — neither may ride along on an allow.
+run $A none  "cd /tmp >$OUT; mv /tmp/a /tmp/b"
+run $A none  "cp -r /tmp/tree /tmp/live; cp /tmp/payload /tmp/live/link"
 
 echo
 [ "$fails" = 0 ] && echo "ALL PASS" || { echo "$fails FAILURES"; exit 1; }