apt-key: warn instead of fail on unreadable keyrings

apt-key has inconsistent behaviour if it can't read a keyring file:
Commands like 'list' skipped silently over such keyrings while 'verify'
failed hard resulting in apt to report cconfusing gpg errors (#834973).

As a first step we teach apt-key to be more consistent here skipping in
all commands over unreadable keyrings, but issuing a warning in the
process, which is as usual for apt commands displayed at the end of the
run.

(cherry picked from commit 105503b4b470c124bc0c271bd8a50e25ecbe9133)
(removed the buffering of warnings in aptwarnings.log, as we do not
 have a cleanup function where we can cat it)

LP: #1642386

2 files changed, 50 insertions, 26 deletions

diff --git a/cmdline/apt-key.in b/cmdline/apt-key.in
index 4f2bc916b..e231d6f61 100644
--- a/cmdline/apt-key.in
+++ b/cmdline/apt-key.in
@@ -224,6 +224,17 @@ remove_key_from_keyring() {
     done
 }
 
+accessible_file_exists() {
+   if ! test -s "$1"; then
+      return 1
+   fi
+   if test -r "$1"; then
+      return 0
+   fi
+   warn "The key(s) in the keyring $1 are ignored as the file is not readable by user '$USER' executing apt-key."
+   return 1
+}
+
 foreach_keyring_do() {
    local ACTION="$1"
    shift
@@ -232,7 +243,7 @@ foreach_keyring_do() {
 	$ACTION "$FORCED_KEYRING" "$@"
    else
 	# otherwise all known keyrings are up for inspection
-	if [ -s "$TRUSTEDFILE" ]; then
+	if accessible_file_exists "$TRUSTEDFILE"; then
 	    $ACTION "$TRUSTEDFILE" "$@"
 	fi
 	local TRUSTEDPARTS="/etc/apt/trusted.gpg.d"
@@ -241,7 +252,7 @@ foreach_keyring_do() {
 	    TRUSTEDPARTS="$(readlink -f "$TRUSTEDPARTS")"
 	    local TRUSTEDPARTSLIST="$(cd /; find "$TRUSTEDPARTS" -mindepth 1 -maxdepth 1 -name '*.gpg')"
 	    for trusted in $(echo "$TRUSTEDPARTSLIST" | sort); do
-		if [ -s "$trusted" ]; then
+		if accessible_file_exists "$trusted"; then
 		    $ACTION "$trusted" "$@"
 		fi
 	    done
@@ -294,35 +305,18 @@ import_keyring_into_keyring() {
     fi
 }
 
+catfile() {
+   cat "$1" >> "$2"
+}
+
 merge_all_trusted_keyrings_into_pubring() {
     # does the same as:
     # foreach_keyring_do 'import_keys_from_keyring' "${GPGHOMEDIR}/pubring.gpg"
     # but without using gpg, just cat and find
     local PUBRING="$(readlink -f "${GPGHOMEDIR}/pubring.gpg")"
-    # if a --keyring was given, just use this one
-    if [ -n "$FORCED_KEYRING" ]; then
-	if [ -s "$FORCED_KEYRING" ]; then
-	    cp --dereference "$FORCED_KEYRING" "$PUBRING"
-	fi
-    else
-	# otherwise all known keyrings are merged
-	local TRUSTEDPARTS="/etc/apt/trusted.gpg.d"
-	eval $(apt-config shell TRUSTEDPARTS Dir::Etc::TrustedParts/d)
-	if [ -d "$TRUSTEDPARTS" ]; then
-	    rm -f "$PUBRING"
-	    if [ -s "$TRUSTEDFILE" ]; then
-		cat "$TRUSTEDFILE" > "$PUBRING"
-	    fi
-	    TRUSTEDPARTS="$(readlink -f "$TRUSTEDPARTS")"
-	    (cd /; find "$TRUSTEDPARTS" -mindepth 1 -maxdepth 1 -name '*.gpg' -exec cat {} + >> "$PUBRING";)
-	elif [ -s "$TRUSTEDFILE" ]; then
-	    cp --dereference "$TRUSTEDFILE" "$PUBRING"
-	fi
-    fi
-
-    if [ ! -s "$PUBRING" ]; then
-	touch "$PUBRING"
-    fi
+    rm -f "$PUBRING"
+    touch "$PUBRING"
+    foreach_keyring_do 'catfile' "$PUBRING"
 }
 
 import_keys_from_keyring() {
@@ -472,6 +466,10 @@ if [ -z "$command" ]; then
 fi
 shift
 
+warn() {
+    echo >&2 'W:' "$@"
+}
+
 create_gpg_home() {
     # gpg needs (in different versions more or less) files to function correctly,
     # so we give it its own homedir and generate some valid content for it later on
diff --git a/test/integration/test-apt-key b/test/integration/test-apt-key
index ddb9bf9d2..1929550c6 100755
--- a/test/integration/test-apt-key
+++ b/test/integration/test-apt-key
@@ -82,6 +82,21 @@ gpg:              unchanged: 1' aptkey --fakeroot update
 	testsuccess --nomsg aptkey --fakeroot del d141dbac8dae
 	testempty aptkey list
 
+	if [ "$(id -u)" != '0' ]; then
+		msgtest 'Test key removal with' 'unreadable key'
+		cleanplate
+		cp -a "keys/joesixpack.pub" "rootdir/etc/apt/trusted.gpg.d/joesixpack.gpg"
+		echo 'foobar' > "rootdir/etc/apt/trusted.gpg.d/unreadablekey.gpg"
+		chmod 000 "rootdir/etc/apt/trusted.gpg.d/unreadablekey.gpg"
+		aptkey --fakeroot del d141dbac8dae
+		testwarning --nomsg aptkey --fakeroot del d141dbac8dae
+		testwarning aptkey list
+		chmod 644 "rootdir/etc/apt/trusted.gpg.d/unreadablekey.gpg"
+		rm -f "rootdir/etc/apt/trusted.gpg.d/unreadablekey.gpg"
+		grep -v '^W: ' "rootdir/tmp/testwarning.output" > "rootdir/aptkeylist.output" || true
+		testempty cat "rootdir/aptkeylist.output"
+	fi
+
 	msgtest 'Test key removal with' 'single key in real file'
 	cleanplate
 	cp -a keys/joesixpack.pub rootdir/etc/apt/trusted.gpg.d/joesixpack.gpg
@@ -189,6 +204,17 @@ gpg:              unchanged: 1' aptkey --fakeroot update
 		msgtest 'Test verify a file' 'with all keys'
 		testsuccess --nomsg aptkey --quiet --readonly verify signature.gpg signature
 
+		if [ "$(id -u)" != '0' ]; then
+			msgtest 'Test verify a file' 'with unreadable key'
+			echo 'foobar' > "rootdir/etc/apt/trusted.gpg.d/unreadablekey.gpg"
+			chmod 000 "rootdir/etc/apt/trusted.gpg.d/unreadablekey.gpg"
+			aptkey --quiet --readonly verify "signature.gpg" "signature"
+			testwarning --nomsg aptkey --quiet --readonly verify "signature.gpg" "signature"
+			testwarning aptkey list
+			chmod 644 "rootdir/etc/apt/trusted.gpg.d/unreadablekey.gpg"
+			rm -f "rootdir/etc/apt/trusted.gpg.d/unreadablekey.gpg"
+		fi
+
 		msgtest 'Test verify a file' 'with good keyring'
 		testsuccess --nomsg aptkey --quiet --readonly --keyring keys/testcase-multikey.pub verify signature.gpg signature