[PATCH 4/4] iotests/308: Test allow-other

From: Max Reitz <mreitz@redhat.com>
To: qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
	qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>
Subject: [PATCH 4/4] iotests/308: Test allow-other
Date: Mon, 14 Jun 2021 16:44:07 +0200	[thread overview]
Message-ID: <20210614144407.134243-5-mreitz@redhat.com> (raw)
In-Reply-To: <20210614144407.134243-1-mreitz@redhat.com>

We cannot reasonably test the main point of allow-other, which is to
allow users other than the current one to access the FUSE export,
because that would require access to sudo, which this test most likely
will not have.  (Also, we would need to figure out some user/group that
is on the machine and that is not the current user/group, which may
become a bit hairy.)

But we can test some byproducts: First, whether changing permissions
works (our FUSE code only allows so for allow-other=true), and second,
whether the kernel applies permission checks with allow-other=true
(because that implies default_permissions).

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 tests/qemu-iotests/308     | 91 ++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/308.out | 47 ++++++++++++++++++++
 2 files changed, 138 insertions(+)

diff --git a/tests/qemu-iotests/308 b/tests/qemu-iotests/308
index f122065d0f..1b2f908947 100755
--- a/tests/qemu-iotests/308
+++ b/tests/qemu-iotests/308
@@ -334,6 +334,97 @@ echo '=== Compare copy with original ==='
 
 $QEMU_IMG compare -f raw -F $IMGFMT "$COPIED_IMG" "$TEST_IMG"
 
+echo
+echo '=== Test permissions ==='
+
+# Test that you can only change permissions on the export with allow-other=true.
+# We cannot really test the primary reason behind allow-other (i.e. to allow
+# users other than the current one access to the export), because for that we
+# would need sudo, which realistically nobody will allow this test to use.
+# What we can do is test that allow-other=true also enables default_permissions,
+# i.e. whether we can still read from the file if we remove the read permission.
+
+# $1: allow-other value ('true' or 'false')
+run_permission_test()
+{
+    # Below, we want to test permission checks on the export.  To do that
+    # properly, we need to ensure that those checks are not bypassed, so we have
+    # to drop cap_dac_override.
+    # (Note that cap_dac_read_search bypasses read permission checks, which is
+    # why we try to open the file R/W below, so we do not have to care about
+    # cap_dac_read_search here.)
+    # $capsh is effectively a shell command, i.e. can be used like:
+    #   $capsh -c "$command $args..."
+    # By default it is just bash.
+    capsh='/usr/bin/env bash'
+    if type -p capsh > /dev/null; then
+        if ! capsh --has-p=cap_dac_override 2>/dev/null; then
+            # No cap_dac_override, we are good to go
+            true # pass
+        elif capsh --has-p=cap_setpcap 2>/dev/null; then
+            # We will need to drop cap_dac_override, but doing so requires
+            # cap_setpcap in turn
+            capsh='capsh --drop=cap_dac_override --'
+        else
+            # Hopefully a rare case
+            _notrun 'CAP_DAC_OVERRIDE must be dropped, but this cannot be' \
+                    'done without CAP_SETPCAP'
+        fi
+    elif [ "$(id -u)" -ne 0 ]; then
+        # Non-root users probably do not have those capabilities, so try to get
+        # by without capsh
+        true # pass
+    else
+        # Running this test as root without capsh on the system should be a rare
+        # case...
+        _notrun 'No capsh found while run as root'
+    fi
+
+    _launch_qemu \
+        -blockdev \
+        "$IMGFMT,node-name=node-format,file.driver=file,file.filename=$TEST_IMG"
+
+    _send_qemu_cmd $QEMU_HANDLE \
+        "{'execute': 'qmp_capabilities'}" \
+        'return'
+
+    # Writable so we can open it R/W below
+    fuse_export_add 'export' \
+        "'mountpoint': '$EXT_MP',
+         'writable': true,
+         'allow-other': $1"
+
+    echo '(Invoking chmod)'
+    chmod 666 "$EXT_MP" 2>&1 | _filter_testdir | _filter_imgfmt
+    stat -c 'Permissions post-chmod: %a' "$EXT_MP"
+
+    echo '(Removing all permissions)'
+    chmod 000 "$EXT_MP" 2>&1 | _filter_testdir | _filter_imgfmt
+
+    # We want a permission denied here (with allow-other=true)
+    # (Use $QEMU_IO_PROG, because $capsh will not know the wrapper that is
+    # $QEMU_IO)
+    # Use blkdebug to force-take the WRITE permission so this will definitely
+    # try to open the export with O_RDWR.
+    imgopts="driver=blkdebug,take-child-perms.0=write,"
+    imgopts+="image.driver=file,image.filename=$EXT_MP"
+    $capsh -c "$QEMU_IO_PROG -c quit --image-opts '$imgopts'" 2>&1 \
+        | _filter_qemu_io | _filter_testdir | _filter_imgfmt
+
+    _send_qemu_cmd $QEMU_HANDLE \
+        "{'execute': 'quit'}" \
+        'return'
+
+    wait=yes _cleanup_qemu
+}
+
+for ao in 'false' 'true'; do
+    echo
+    echo "--- allow-other=$ao ---"
+
+    run_permission_test "$ao"
+done
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/308.out b/tests/qemu-iotests/308.out
index 466e7e0267..4620efbb0d 100644
--- a/tests/qemu-iotests/308.out
+++ b/tests/qemu-iotests/308.out
@@ -167,4 +167,51 @@ OK: Post-truncate image size is as expected
 
 === Compare copy with original ===
 Images are identical.
+
+=== Test permissions ===
+
+--- allow-other=false ---
+{'execute': 'qmp_capabilities'}
+{"return": {}}
+{'execute': 'block-export-add',
+          'arguments': {
+              'type': 'fuse',
+              'id': 'export',
+              'node-name': 'node-format',
+              'mountpoint': 'TEST_DIR/t.IMGFMT.fuse',
+         'writable': true,
+         'allow-other': false
+          } }
+{"return": {}}
+(Invoking chmod)
+chmod: changing permissions of 'TEST_DIR/t.IMGFMT.fuse': Operation not supported
+Permissions post-chmod: 600
+(Removing all permissions)
+chmod: changing permissions of 'TEST_DIR/t.IMGFMT.fuse': Operation not supported
+{'execute': 'quit'}
+{"return": {}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "export"}}
+
+--- allow-other=true ---
+{'execute': 'qmp_capabilities'}
+{"return": {}}
+{'execute': 'block-export-add',
+          'arguments': {
+              'type': 'fuse',
+              'id': 'export',
+              'node-name': 'node-format',
+              'mountpoint': 'TEST_DIR/t.IMGFMT.fuse',
+         'writable': true,
+         'allow-other': true
+          } }
+{"return": {}}
+(Invoking chmod)
+Permissions post-chmod: 666
+(Removing all permissions)
+qemu-io: can't open: Could not open 'TEST_DIR/t.IMGFMT.fuse': Permission denied
+{'execute': 'quit'}
+{"return": {}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "export"}}
 *** done
-- 
2.31.1


