Prevent overflow when calculating ulog block size

In kdb_log.c:resize(), log an error and fail if the update size is
larger than the largest possible block size (2^16-1).

CVE-2025-24528:

In MIT krb5 release 1.7 and later with incremental propagation
enabled, an authenticated attacker can cause kadmind to write beyond
the end of the mapped region for the iprop log file, likely causing a
process crash.

[ghudson@mit.edu: edited commit message and added CVE description]

(cherry picked from commit 78ceba024b64d49612375be4a12d1c066b0bfbd0)

ticket: 9159
version_fixed: 1.21.4

diff --git a/src/lib/kdb/kdb_log.c b/src/lib/kdb/kdb_log.c
index 2659a250187ff6519f7fcb01905ce17a6ac1f0bf..68fae919a529354ea32b3e62bf21c77d73df60b9 100644 (file)
--- a/src/lib/kdb/kdb_log.c
+++ b/src/lib/kdb/kdb_log.c
@@ -183,7 +183,7 @@ extend_file_to(int fd, unsigned int new_size)
  */
 static krb5_error_code
 resize(kdb_hlog_t *ulog, uint32_t ulogentries, int ulogfd,
-       unsigned int recsize)
+       unsigned int recsize, const kdb_incr_update_t *upd)
 {
     unsigned int new_block, new_size;
 
@@ -195,6 +195,12 @@ resize(kdb_hlog_t *ulog, uint32_t ulogentries, int ulogfd,
     new_block *= ULOG_BLOCK;
     new_size += ulogentries * new_block;
 
+    if (new_block > UINT16_MAX) {
+        syslog(LOG_ERR, _("ulog overflow caused by principal %.*s"),
+               upd->kdb_princ_name.utf8str_t_len,
+               upd->kdb_princ_name.utf8str_t_val);
+        return KRB5_LOG_ERROR;
+    }
     if (new_size > MAXLOGLEN)
         return KRB5_LOG_ERROR;
 
@@ -291,7 +297,7 @@ store_update(kdb_log_context *log_ctx, kdb_incr_update_t *upd)
     recsize = sizeof(kdb_ent_header_t) + upd_size;
 
     if (recsize > ulog->kdb_block) {
-        retval = resize(ulog, ulogentries, log_ctx->ulogfd, recsize);
+        retval = resize(ulog, ulogentries, log_ctx->ulogfd, recsize, upd);
         if (retval)
             return retval;
     }