iotests/308: Fix for CAP_DAC_OVERRIDE

With CAP_DAC_OVERRIDE (which e.g. root generally has), permission checks
will be bypassed when opening files.

308 in one instance tries to open a read-only file (FUSE export) with
qemu-io as read/write, and expects this to fail.  However, when running
it as root, opening will succeed (thanks to CAP_DAC_OVERRIDE) and only
the actual write operation will fail.

Note this as "Case not run", but have the test pass in either case.

Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Fixes: 2c7dd057aa7bd7a875e9b1a53975c220d6380bc4
       ("export/fuse: Pass default_permissions for mount")
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220103120014.13061-1-hreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 24 insertions, 3 deletions

diff --git a/tests/qemu-iotests/308 b/tests/qemu-iotests/308
index 2e3f8f4..bde4aac 100755
--- a/tests/qemu-iotests/308
+++ b/tests/qemu-iotests/308
@@ -230,8 +230,29 @@ echo '=== Writable export ==='
 fuse_export_add 'export-mp' "'mountpoint': '$EXT_MP', 'writable': true"
 
 # Check that writing to the read-only export fails
-$QEMU_IO -f raw -c 'write -P 42 1M 64k' "$TEST_IMG" 2>&1 \
-    | _filter_qemu_io | _filter_testdir | _filter_imgfmt
+output=$($QEMU_IO -f raw -c 'write -P 42 1M 64k' "$TEST_IMG" 2>&1 \
+             | _filter_qemu_io | _filter_testdir | _filter_imgfmt)
+
+# Expected reference output: Opening the file fails because it has no
+# write permission
+reference="Could not open 'TEST_DIR/t.IMGFMT': Permission denied"
+
+if echo "$output" | grep -q "$reference"; then
+    echo "Writing to read-only export failed: OK"
+elif echo "$output" | grep -q "write failed: Permission denied"; then
+    # With CAP_DAC_OVERRIDE (e.g. when running this test as root), the export
+    # can be opened regardless of its file permissions, but writing will then
+    # fail.  This is not the result for which we want to test, so count this as
+    # a SKIP.
+    _casenotrun "Opening RO export as R/W succeeded, perhaps because of" \
+        "CAP_DAC_OVERRIDE"
+
+    # Still, write this to the reference output to make the test pass
+    echo "Writing to read-only export failed: OK"
+else
+    echo "Writing to read-only export failed: ERROR"
+    echo "$output"
+fi
 
 # But here it should work
 $QEMU_IO -f raw -c 'write -P 42 1M 64k' "$EXT_MP" | _filter_qemu_io
diff --git a/tests/qemu-iotests/308.out b/tests/qemu-iotests/308.out
index fc47bb1..e4467a1 100644
--- a/tests/qemu-iotests/308.out
+++ b/tests/qemu-iotests/308.out
@@ -95,7 +95,7 @@ virtual size: 0 B (0 bytes)
               'mountpoint': 'TEST_DIR/t.IMGFMT.fuse', 'writable': true
           } }
 {"return": {}}
-qemu-io: can't open device TEST_DIR/t.IMGFMT: Could not open 'TEST_DIR/t.IMGFMT': Permission denied
+Writing to read-only export failed: OK
 wrote 65536/65536 bytes at offset 1048576
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 65536/65536 bytes at offset 1048576