Re: [PATCH] storage: Add support to set{uid,gid} and sticky bit

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On Wed, Feb 19, 2020 at 05:51:44PM -0300, Julio Faracco wrote:
This commit add more features to storages that supports setuid, setgid
and sticky bit. This extend some permission levels of volumes when you
run an hypervisor using a specific user that can run but cannot delete
volumes for instance.

I'm confused about the use case here - volumes should not be executable
and setuid/setgid only make sense on executable files.

Additionally, when you create a directory without
`pool-build` command, you cannot import those extra permissions.
Example:

   # mkdir /var/lib/libvirt/images/
   # chmod 0755 /var/lib/libvirt/images/
   # chmod u+s /var/lib/libvirt/images/
   # pool-start default
   # pool-dumpxml default

No setuid from `<mode>0755</mode>`.
Output should expect `<mode>4755</mode>`.


FYI I proposed a similar patch ~7.5 years ago (and still haven't
bothered to resend it O:-)):
https://www.redhat.com/archives/libvir-list/2012-August/msg00687.html
https://www.redhat.com/archives/libvir-list/2012-August/msg01004.html

The consensus seemed to be
* not wanting to touch the SGID/SUID bits
* reporting the perms should be OK

For regular files, these bits seem to be useless for volumes, I think
we should reject them.
For directories, SGID and sticky might make sense

Signed-off-by: Julio Faracco <jcfaracco@xxxxxxxxx>
---
src/conf/storage_conf.c    | 11 ++++++++---
src/storage/storage_util.c | 12 ++++++++----
2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/conf/storage_conf.c b/src/conf/storage_conf.c
index 252d28cbfb..54e4a60ded 100644
--- a/src/conf/storage_conf.c
+++ b/src/conf/storage_conf.c
@@ -746,7 +746,7 @@ virStorageDefParsePerms(xmlXPathContextPtr ctxt,
    if ((mode = virXPathString("string(./mode)", ctxt))) {
        int tmp;

-        if (virStrToLong_i(mode, NULL, 8, &tmp) < 0 || (tmp & ~0777)) {
+        if (virStrToLong_i(mode, NULL, 8, &tmp) < 0 || (tmp & ~07777)) {
            virReportError(VIR_ERR_XML_ERROR, "%s",
                           _("malformed octal mode"));
            goto error;

To loosen this check, I'd rather see a new check added in the callers of
this function, to make sure we won't allow creating a suid volume.

@@ -1187,9 +1187,14 @@ virStoragePoolDefFormatBuf(virBufferPtr buf,
            def->target.perms.label) {
            virBufferAddLit(buf, "<permissions>\n");
            virBufferAdjustIndent(buf, 2);
-            if (def->target.perms.mode != (mode_t) -1)
-                virBufferAsprintf(buf, "<mode>0%o</mode>\n",
+            if (def->target.perms.mode != (mode_t) -1) {
+                if (def->target.perms.mode & (S_ISUID | S_ISGID | S_ISVTX))
+                    virBufferAsprintf(buf, "<mode>%4o</mode>\n",

Wouldn't this print it without the leading zero?

                                  def->target.perms.mode);
+                else
+                    virBufferAsprintf(buf, "<mode>0%o</mode>\n",
+                                      def->target.perms.mode);
+            }
            if (def->target.perms.uid != (uid_t) -1)
                virBufferAsprintf(buf, "<owner>%d</owner>\n",
                                  (int) def->target.perms.uid);
diff --git a/src/storage/storage_util.c b/src/storage/storage_util.c
index c2754dbb93..5352ab9120 100644
--- a/src/storage/storage_util.c
+++ b/src/storage/storage_util.c
@@ -82,6 +82,10 @@ VIR_LOG_INIT("storage.storage_util");
# define S_IRWXUGO (S_IRWXU | S_IRWXG | S_IRWXO)
#endif

+#ifndef S_IALLUGO
+# define S_IALLUGO (S_ISUID | S_ISGID | S_ISVTX | S_IRWXUGO)
+#endif
+
/* virStorageBackendNamespaceInit:
 * @poolType: virStoragePoolType
 * @xmlns: Storage Pool specific namespace callback methods
@@ -512,7 +516,7 @@ virStorageBackendCreateExecCommand(virStoragePoolObjPtr pool,

        virCommandSetUID(cmd, vol->target.perms->uid);
        virCommandSetGID(cmd, vol->target.perms->gid);
-        virCommandSetUmask(cmd, S_IRWXUGO ^ mode);
+        virCommandSetUmask(cmd, S_IALLUGO ^ mode);

        if (virCommandRun(cmd, NULL) == 0) {
            /* command was successfully run, check if the file was created */
@@ -523,7 +527,7 @@ virStorageBackendCreateExecCommand(virStoragePoolObjPtr pool,
                 * If that doesn't match what we expect, then let's try to
                 * re-open the file and attempt to force the mode change.
                 */
-                if (mode != (st.st_mode & S_IRWXUGO)) {
+                if (mode != (st.st_mode & S_IALLUGO)) {
                    VIR_AUTOCLOSE fd = -1;
                    int flags = VIR_FILE_OPEN_FORK | VIR_FILE_OPEN_FORCE_MODE;

@@ -569,7 +573,7 @@ virStorageBackendCreateExecCommand(virStoragePoolObjPtr pool,
        goto cleanup;
    }

-    if (mode != (st.st_mode & S_IRWXUGO) &&
+    if (mode != (st.st_mode & S_IALLUGO) &&
        chmod(vol->target.path, mode) < 0) {
        virReportSystemError(errno,
                             _("cannot set mode of '%s' to %04o"),

The checks above are for volume creation and IMO should stay.

Jano

@@ -1825,7 +1829,7 @@ virStorageBackendUpdateVolTargetInfoFD(virStorageSourcePtr target,

    if (!target->perms && VIR_ALLOC(target->perms) < 0)
        return -1;
-    target->perms->mode = sb->st_mode & S_IRWXUGO;
+    target->perms->mode = sb->st_mode & S_IALLUGO;
    target->perms->uid = sb->st_uid;
    target->perms->gid = sb->st_gid;

--
2.20.1


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