xnu-2782.20.48.tar.gz

[apple/xnu.git] / bsd / kern / sysv_ipc.c

diff --git a/bsd/kern/sysv_ipc.c b/bsd/kern/sysv_ipc.c
index a47e59f2040b62109b678d695472966ecf6bfc48..8f56757c4b7f24233683cf289a2140011d8bf24c 100644 (file)
--- a/bsd/kern/sysv_ipc.c
+++ b/bsd/kern/sysv_ipc.c
@@ -60,39 +60,101 @@
 
 #include <sys/param.h>
 #include <sys/ipc.h>
+#include <sys/stat.h>  /* mode constants */
 #include <sys/ucred.h>
 #include <sys/kauth.h>
 
 
 /*
  * Check for ipc permission
- *
- * XXX: Should pass proc argument so that we can pass 
- * XXX: proc->p_acflag to suser()
  */
 
+
+/*
+ * ipc_perm
+ *
+ *     perm->mode                      mode of the object
+ *     mode                            mode bits we want to test
+ *
+ * Returns:    0                       Success
+ *             EPERM
+ *             EACCES
+ *
+ * Notes:      The IPC_M bit is special, in that it may only be granted to
+ *             root, the creating user, or the owning user.
+ *
+ *             This code does not use posix_cred_access() because of the
+ *             need to check both creator and owner separately when we are
+ *             considering a rights grant.  Because of this, we need to do
+ *             two evaluations when the values are inequal, which can lead
+ *             us to defeat the callout avoidance optimization.  So we do
+ *             the work here, inline.  This is less than optimal for any
+ *             future work involving opacity of of POSIX credentials.
+ *
+ *             Setting up the mode_owner / mode_group / mode_world implicitly
+ *             masks the IPC_M bit off.  This is intentional.
+ *
+ *             See the posix_cred_access() implementation for algorithm
+ *             information.
+ */
 int
-ipcperm(kauth_cred_t cred, struct ipc_perm *perm, int mode)
+ipcperm(kauth_cred_t cred, struct ipc_perm *perm, int mode_req)
 {
+       uid_t   uid = kauth_cred_getuid(cred);  /* avoid multiple calls */
+       int     want_mod_controlinfo = (mode_req & IPC_M);
+       int     is_member;
+       mode_t  mode_owner = (perm->mode & S_IRWXU);
+       mode_t  mode_group = (perm->mode & S_IRWXG) << 3;
+       mode_t  mode_world = (perm->mode & S_IRWXO) << 6;
 
+       /* Grant all rights to super user */
        if (!suser(cred, (u_short *)NULL))
                return (0);
 
-       /* Check for user match. */
-       if (kauth_cred_getuid(cred) != perm->cuid && kauth_cred_getuid(cred) != perm->uid) {
-               int is_member;
+       /* Grant or deny rights based on ownership */
+       if (uid == perm->cuid || uid == perm->uid) {
+               if (want_mod_controlinfo)
+                       return (0);
 
-               if (mode & IPC_M)
+               return ((mode_req & mode_owner) == mode_req ? 0 : EACCES);
+       } else {
+               /* everyone else who wants to modify control info is denied */
+               if (want_mod_controlinfo)
                        return (EPERM);
-               /* Check for group match. */
-               mode >>= 3;
-               if ((kauth_cred_ismember_gid(cred, perm->gid, &is_member) || !is_member) &&
-                   (kauth_cred_ismember_gid(cred, perm->cgid, &is_member) || !is_member))
-                       /* Check for `other' match. */
-                       mode >>= 3;
        }
 
-       if (mode & IPC_M)
+       /*
+        * Combined group and world rights check, if no owner rights; positive
+        * asssertion of gid/cgid equality avoids an extra callout in the
+        * common case.
+        */
+       if ((mode_req & mode_group & mode_world) == mode_req) {
                return (0);
-       return ((mode & perm->mode) == mode ? 0 : EACCES);
+       } else {
+               if ((mode_req & mode_group) != mode_req) {
+                       if ((!kauth_cred_ismember_gid(cred, perm->gid, &is_member) && is_member) &&
+                           ((perm->gid == perm->cgid) ||
+                            (!kauth_cred_ismember_gid(cred, perm->cgid, &is_member) && is_member))) {
+                               return (EACCES);
+                       } else {
+                               if ((mode_req & mode_world) != mode_req) {
+                                       return (EACCES);
+                               } else {
+                                       return (0);
+                               }
+                       }
+               } else {
+                       if ((!kauth_cred_ismember_gid(cred, perm->gid, &is_member) && is_member) ||
+                           ((perm->gid != perm->cgid) &&
+                            (!kauth_cred_ismember_gid(cred, perm->cgid, &is_member) && is_member))) {
+                               return (0);
+                       } else {
+                               if ((mode_req & mode_world) != mode_req) {
+                                       return (EACCES);
+                               } else {
+                                       return (0);
+                               }
+                       }
+               }
+       }
 }