[xen stable-4.14] tools/xenstore: fix checking node permissions

[patchbot@xxxxxxx]

commit 2761f00a40665e97e1851880089fc888b378efc7
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue Sep 13 07:35:10 2022 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Nov 1 15:20:41 2022 +0000

    tools/xenstore: fix checking node permissions
    
    Today chk_domain_generation() is being used to check whether a node
    permission entry is still valid or whether it is referring to a domain
    no longer existing. This is done by comparing the node's and the
    domain's generation count.
    
    In case no struct domain is existing for a checked domain, but the
    domain itself is valid, chk_domain_generation() assumes it is being
    called due to the first node created for a new domain and it will
    return success.
    
    This might be wrong in case the checked permission is related to an
    old domain, which has just been replaced with a new domain using the
    same domid.
    
    Fix that by letting chk_domain_generation() fail in case a struct
    domain isn't found. In order to cover the case of the first node for
    a new domain try to allocate the needed struct domain explicitly when
    processing the related SET_PERMS command. In case a referenced domain
    isn't existing, flag the related permission to be ignored right away.
    
    This is XSA-417 / CVE-2022-42320.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
    (cherry picked from commit ab128218225d3542596ca3a02aee80d55494bef8)
---
 tools/xenstore/xenstored_core.c   |  5 +++++
 tools/xenstore/xenstored_domain.c | 37 +++++++++++++++++++++++++------------
 tools/xenstore/xenstored_domain.h |  1 +
 3 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 28724ef10a..34a8469dd6 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -1642,6 +1642,11 @@ static int do_set_perms(const void *ctx, struct 
connection *conn,
        if (!xs_strings_to_perms(perms.p, perms.num, permstr))
                return errno;
 
+       if (domain_alloc_permrefs(&perms) < 0)
+               return ENOMEM;
+       if (perms.p[0].perms & XS_PERM_IGNORE)
+               return ENOENT;
+
        /* First arg is node name. */
        if (strstarts(in->buffer, "@")) {
                if (set_perms_special(conn, in->buffer, &perms))
diff --git a/tools/xenstore/xenstored_domain.c 
b/tools/xenstore/xenstored_domain.c
index 417ff81181..8dcc1c20ab 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -859,7 +859,6 @@ int domain_entry_inc(struct connection *conn, struct node 
*node)
  * count (used for testing whether a node permission is older than a domain).
  *
  * Return values:
- * -1: error
  *  0: domain has higher generation count (it is younger than a node with the
  *     given count), or domain isn't existing any longer
  *  1: domain is older than the node
@@ -867,20 +866,38 @@ int domain_entry_inc(struct connection *conn, struct node 
*node)
 static int chk_domain_generation(unsigned int domid, uint64_t gen)
 {
        struct domain *d;
-       xc_dominfo_t dominfo;
 
        if (!xc_handle && domid == 0)
                return 1;
 
        d = find_domain_struct(domid);
-       if (d)
-               return (d->generation <= gen) ? 1 : 0;
 
-       if (!get_domain_info(domid, &dominfo))
-               return 0;
+       return (d && d->generation <= gen) ? 1 : 0;
+}
 
-       d = alloc_domain(NULL, domid);
-       return d ? 1 : -1;
+/*
+ * Allocate all missing struct domain referenced by a permission set.
+ * Any permission entries for not existing domains will be marked to be
+ * ignored.
+ */
+int domain_alloc_permrefs(struct node_perms *perms)
+{
+       unsigned int i, domid;
+       struct domain *d;
+       xc_dominfo_t dominfo;
+
+       for (i = 0; i < perms->num; i++) {
+               domid = perms->p[i].id;
+               d = find_domain_struct(domid);
+               if (!d) {
+                       if (!get_domain_info(domid, &dominfo))
+                               perms->p[i].perms |= XS_PERM_IGNORE;
+                       else if (!alloc_domain(NULL, domid))
+                               return ENOMEM;
+               }
+       }
+
+       return 0;
 }
 
 /*
@@ -893,8 +910,6 @@ int domain_adjust_node_perms(struct connection *conn, 
struct node *node)
        int ret;
 
        ret = chk_domain_generation(node->perms.p[0].id, node->generation);
-       if (ret < 0)
-               return errno;
 
        /* If the owner doesn't exist any longer give it to priv domain. */
        if (!ret) {
@@ -911,8 +926,6 @@ int domain_adjust_node_perms(struct connection *conn, 
struct node *node)
                        continue;
                ret = chk_domain_generation(node->perms.p[i].id,
                                            node->generation);
-               if (ret < 0)
-                       return errno;
                if (!ret)
                        node->perms.p[i].perms |= XS_PERM_IGNORE;
        }
diff --git a/tools/xenstore/xenstored_domain.h 
b/tools/xenstore/xenstored_domain.h
index 732eb8fa75..bab405209e 100644
--- a/tools/xenstore/xenstored_domain.h
+++ b/tools/xenstore/xenstored_domain.h
@@ -65,6 +65,7 @@ bool domain_is_unprivileged(struct connection *conn);
 
 /* Remove node permissions for no longer existing domains. */
 int domain_adjust_node_perms(struct connection *conn, struct node *node);
+int domain_alloc_permrefs(struct node_perms *perms);
 
 /* Quota manipulation */
 int domain_entry_inc(struct connection *conn, struct node *);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.14