[xen staging] tools/xenstore: rework path length check

[patchbot@xxxxxxx]

commit 924bf8c793cb1fee303c83f50632c68426cf8f12
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue Dec 15 16:04:11 2020 +0100
Commit:     Wei Liu <wl@xxxxxxx>
CommitDate: Tue Dec 15 15:55:38 2020 +0000

    tools/xenstore: rework path length check
    
    The different fixed limits for absolute and relative path lengths of
    Xenstore nodes make it possible to create per-domain nodes via
    absolute paths which are not accessible using relative paths, as the
    two limits differ by 1024 characters.
    
    Instead of this weird limits use only one limit, which applies to the
    relative path length of per-domain nodes and to the absolute path
    length of all other nodes. This means, the path length check is
    applied to the path after removing a possible start of
    "/local/domain/<n>/" with <n> being a domain id.
    
    There has been the request to be able to limit the path lengths even
    more, so an additional quota is added which can be applied to path
    lengths. It is XENSTORE_REL_PATH_MAX (2048) per default, but can be
    set to lower values. This is done via the new "-M" or "--path-max"
    option when invoking xenstored.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Wei Liu <wl@xxxxxxx>
---
 tools/xenstore/xenstored_core.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 746a1247b3..3082a36d3a 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -102,6 +102,7 @@ int quota_nb_watch_per_domain = 128;
 int quota_max_entry_size = 2048; /* 2K */
 int quota_max_transaction = 10;
 int quota_nb_perms_per_node = 5;
+int quota_max_path_len = XENSTORE_REL_PATH_MAX;
 
 void trace(const char *fmt, ...)
 {
@@ -734,6 +735,9 @@ static bool valid_chars(const char *node)
 
 bool is_valid_nodename(const char *node)
 {
+       int local_off = 0;
+       unsigned int domid;
+
        /* Must start in /. */
        if (!strstarts(node, "/"))
                return false;
@@ -746,7 +750,10 @@ bool is_valid_nodename(const char *node)
        if (strstr(node, "//"))
                return false;
 
-       if (strlen(node) > XENSTORE_ABS_PATH_MAX)
+       if (sscanf(node, "/local/domain/%5u/%n", &domid, &local_off) != 1)
+               local_off = 0;
+
+       if (strlen(node) > local_off + quota_max_path_len)
                return false;
 
        return valid_chars(node);
@@ -806,6 +813,8 @@ static struct node *get_node_canonicalized(struct 
connection *conn,
        if (!canonical_name)
                canonical_name = &tmp_name;
        *canonical_name = canonicalize(conn, ctx, name);
+       if (!*canonical_name)
+               return NULL;
        return get_node(conn, ctx, *canonical_name, perm);
 }
 
@@ -1926,6 +1935,7 @@ static void usage(void)
 "  -W, --watch-nb <nb>     limit the number of watches per domain,\n"
 "  -t, --transaction <nb>  limit the number of transaction allowed per 
domain,\n"
 "  -A, --perm-nb <nb>      limit the number of permissions per node,\n"
+"  -M, --path-max <chars>  limit the allowed Xenstore node path length,\n"
 "  -R, --no-recovery       to request that no recovery should be attempted 
when\n"
 "                          the store is corrupted (debug only),\n"
 "  -I, --internal-db       store database in memory, not on disk\n"
@@ -1947,6 +1957,7 @@ static struct option options[] = {
        { "trace-file", 1, NULL, 'T' },
        { "transaction", 1, NULL, 't' },
        { "perm-nb", 1, NULL, 'A' },
+       { "path-max", 1, NULL, 'M' },
        { "no-recovery", 0, NULL, 'R' },
        { "internal-db", 0, NULL, 'I' },
        { "verbose", 0, NULL, 'V' },
@@ -1969,7 +1980,7 @@ int main(int argc, char *argv[])
        int timeout;
 
 
-       while ((opt = getopt_long(argc, argv, "DE:F:HNPS:t:A:T:RVW:", options,
+       while ((opt = getopt_long(argc, argv, "DE:F:HNPS:t:A:M:T:RVW:", options,
                                  NULL)) != -1) {
                switch (opt) {
                case 'D':
@@ -2014,6 +2025,10 @@ int main(int argc, char *argv[])
                case 'A':
                        quota_nb_perms_per_node = strtol(optarg, NULL, 10);
                        break;
+                       quota_max_path_len = strtol(optarg, NULL, 10);
+                       quota_max_path_len = min(XENSTORE_REL_PATH_MAX,
+                                                quota_max_path_len);
+                       break;
                case 'e':
                        dom0_event = strtol(optarg, NULL, 10);
                        break;
--
generated by git-patchbot for /home/xen/git/xen.git#staging