aboutsummaryrefslogtreecommitdiffstats
path: root/fs/nfsd/nfs4recover.c
diff options
context:
space:
mode:
authorDavid Howells <dhowells@redhat.com>2008-11-13 18:39:23 -0500
committerJames Morris <jmorris@namei.org>2008-11-13 18:39:23 -0500
commitd84f4f992cbd76e8f39c488cf0c5d123843923b1 (patch)
treefc4a0349c42995715b93d0f7a3c78e9ea9b3f36e /fs/nfsd/nfs4recover.c
parent745ca2475a6ac596e3d8d37c2759c0fbe2586227 (diff)
CRED: Inaugurate COW credentials
Inaugurate copy-on-write credentials management. This uses RCU to manage the credentials pointer in the task_struct with respect to accesses by other tasks. A process may only modify its own credentials, and so does not need locking to access or modify its own credentials. A mutex (cred_replace_mutex) is added to the task_struct to control the effect of PTRACE_ATTACHED on credential calculations, particularly with respect to execve(). With this patch, the contents of an active credentials struct may not be changed directly; rather a new set of credentials must be prepared, modified and committed using something like the following sequence of events: struct cred *new = prepare_creds(); int ret = blah(new); if (ret < 0) { abort_creds(new); return ret; } return commit_creds(new); There are some exceptions to this rule: the keyrings pointed to by the active credentials may be instantiated - keyrings violate the COW rule as managing COW keyrings is tricky, given that it is possible for a task to directly alter the keys in a keyring in use by another task. To help enforce this, various pointers to sets of credentials, such as those in the task_struct, are declared const. The purpose of this is compile-time discouragement of altering credentials through those pointers. Once a set of credentials has been made public through one of these pointers, it may not be modified, except under special circumstances: (1) Its reference count may incremented and decremented. (2) The keyrings to which it points may be modified, but not replaced. The only safe way to modify anything else is to create a replacement and commit using the functions described in Documentation/credentials.txt (which will be added by a later patch). This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). This now prepares and commits credentials in various places in the security code rather than altering the current creds directly. (2) Temporary credential overrides. do_coredump() and sys_faccessat() now prepare their own credentials and temporarily override the ones currently on the acting thread, whilst preventing interference from other threads by holding cred_replace_mutex on the thread being dumped. This will be replaced in a future patch by something that hands down the credentials directly to the functions being called, rather than altering the task's objective credentials. (3) LSM interface. A number of functions have been changed, added or removed: (*) security_capset_check(), ->capset_check() (*) security_capset_set(), ->capset_set() Removed in favour of security_capset(). (*) security_capset(), ->capset() New. This is passed a pointer to the new creds, a pointer to the old creds and the proposed capability sets. It should fill in the new creds or return an error. All pointers, barring the pointer to the new creds, are now const. (*) security_bprm_apply_creds(), ->bprm_apply_creds() Changed; now returns a value, which will cause the process to be killed if it's an error. (*) security_task_alloc(), ->task_alloc_security() Removed in favour of security_prepare_creds(). (*) security_cred_free(), ->cred_free() New. Free security data attached to cred->security. (*) security_prepare_creds(), ->cred_prepare() New. Duplicate any security data attached to cred->security. (*) security_commit_creds(), ->cred_commit() New. Apply any security effects for the upcoming installation of new security by commit_creds(). (*) security_task_post_setuid(), ->task_post_setuid() Removed in favour of security_task_fix_setuid(). (*) security_task_fix_setuid(), ->task_fix_setuid() Fix up the proposed new credentials for setuid(). This is used by cap_set_fix_setuid() to implicitly adjust capabilities in line with setuid() changes. Changes are made to the new credentials, rather than the task itself as in security_task_post_setuid(). (*) security_task_reparent_to_init(), ->task_reparent_to_init() Removed. Instead the task being reparented to init is referred directly to init's credentials. NOTE! This results in the loss of some state: SELinux's osid no longer records the sid of the thread that forked it. (*) security_key_alloc(), ->key_alloc() (*) security_key_permission(), ->key_permission() Changed. These now take cred pointers rather than task pointers to refer to the security context. (4) sys_capset(). This has been simplified and uses less locking. The LSM functions it calls have been merged. (5) reparent_to_kthreadd(). This gives the current thread the same credentials as init by simply using commit_thread() to point that way. (6) __sigqueue_alloc() and switch_uid() __sigqueue_alloc() can't stop the target task from changing its creds beneath it, so this function gets a reference to the currently applicable user_struct which it then passes into the sigqueue struct it returns if successful. switch_uid() is now called from commit_creds(), and possibly should be folded into that. commit_creds() should take care of protecting __sigqueue_alloc(). (7) [sg]et[ug]id() and co and [sg]et_current_groups. The set functions now all use prepare_creds(), commit_creds() and abort_creds() to build and check a new set of credentials before applying it. security_task_set[ug]id() is called inside the prepared section. This guarantees that nothing else will affect the creds until we've finished. The calling of set_dumpable() has been moved into commit_creds(). Much of the functionality of set_user() has been moved into commit_creds(). The get functions all simply access the data directly. (8) security_task_prctl() and cap_task_prctl(). security_task_prctl() has been modified to return -ENOSYS if it doesn't want to handle a function, or otherwise return the return value directly rather than through an argument. Additionally, cap_task_prctl() now prepares a new set of credentials, even if it doesn't end up using it. (9) Keyrings. A number of changes have been made to the keyrings code: (a) switch_uid_keyring(), copy_keys(), exit_keys() and suid_keys() have all been dropped and built in to the credentials functions directly. They may want separating out again later. (b) key_alloc() and search_process_keyrings() now take a cred pointer rather than a task pointer to specify the security context. (c) copy_creds() gives a new thread within the same thread group a new thread keyring if its parent had one, otherwise it discards the thread keyring. (d) The authorisation key now points directly to the credentials to extend the search into rather pointing to the task that carries them. (e) Installing thread, process or session keyrings causes a new set of credentials to be created, even though it's not strictly necessary for process or session keyrings (they're shared). (10) Usermode helper. The usermode helper code now carries a cred struct pointer in its subprocess_info struct instead of a new session keyring pointer. This set of credentials is derived from init_cred and installed on the new process after it has been cloned. call_usermodehelper_setup() allocates the new credentials and call_usermodehelper_freeinfo() discards them if they haven't been used. A special cred function (prepare_usermodeinfo_creds()) is provided specifically for call_usermodehelper_setup() to call. call_usermodehelper_setkeys() adjusts the credentials to sport the supplied keyring as the new session keyring. (11) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) selinux_setprocattr() no longer does its check for whether the current ptracer can access processes with the new SID inside the lock that covers getting the ptracer's SID. Whilst this lock ensures that the check is done with the ptracer pinned, the result is only valid until the lock is released, so there's no point doing it inside the lock. (12) is_single_threaded(). This function has been extracted from selinux_setprocattr() and put into a file of its own in the lib/ directory as join_session_keyring() now wants to use it too. The code in SELinux just checked to see whether a task shared mm_structs with other tasks (CLONE_VM), but that isn't good enough. We really want to know if they're part of the same thread group (CLONE_THREAD). (13) nfsd. The NFS server daemon now has to use the COW credentials to set the credentials it is going to use. It really needs to pass the credentials down to the functions it calls, but it can't do that until other patches in this series have been applied. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: James Morris <jmorris@namei.org>
Diffstat (limited to 'fs/nfsd/nfs4recover.c')
-rw-r--r--fs/nfsd/nfs4recover.c68
1 files changed, 42 insertions, 26 deletions
diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 632a50b4b371..9371ea12d7fa 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -54,20 +54,26 @@
54static struct path rec_dir; 54static struct path rec_dir;
55static int rec_dir_init = 0; 55static int rec_dir_init = 0;
56 56
57static void 57static int
58nfs4_save_user(uid_t *saveuid, gid_t *savegid) 58nfs4_save_creds(const struct cred **original_creds)
59{ 59{
60 *saveuid = current->cred->fsuid; 60 struct cred *new;
61 *savegid = current->cred->fsgid; 61
62 current->cred->fsuid = 0; 62 new = prepare_creds();
63 current->cred->fsgid = 0; 63 if (!new)
64 return -ENOMEM;
65
66 new->fsuid = 0;
67 new->fsgid = 0;
68 *original_creds = override_creds(new);
69 put_cred(new);
70 return 0;
64} 71}
65 72
66static void 73static void
67nfs4_reset_user(uid_t saveuid, gid_t savegid) 74nfs4_reset_creds(const struct cred *original)
68{ 75{
69 current->cred->fsuid = saveuid; 76 revert_creds(original);
70 current->cred->fsgid = savegid;
71} 77}
72 78
73static void 79static void
@@ -129,10 +135,9 @@ nfsd4_sync_rec_dir(void)
129int 135int
130nfsd4_create_clid_dir(struct nfs4_client *clp) 136nfsd4_create_clid_dir(struct nfs4_client *clp)
131{ 137{
138 const struct cred *original_cred;
132 char *dname = clp->cl_recdir; 139 char *dname = clp->cl_recdir;
133 struct dentry *dentry; 140 struct dentry *dentry;
134 uid_t uid;
135 gid_t gid;
136 int status; 141 int status;
137 142
138 dprintk("NFSD: nfsd4_create_clid_dir for \"%s\"\n", dname); 143 dprintk("NFSD: nfsd4_create_clid_dir for \"%s\"\n", dname);
@@ -140,7 +145,9 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
140 if (!rec_dir_init || clp->cl_firststate) 145 if (!rec_dir_init || clp->cl_firststate)
141 return 0; 146 return 0;
142 147
143 nfs4_save_user(&uid, &gid); 148 status = nfs4_save_creds(&original_cred);
149 if (status < 0)
150 return status;
144 151
145 /* lock the parent */ 152 /* lock the parent */
146 mutex_lock(&rec_dir.dentry->d_inode->i_mutex); 153 mutex_lock(&rec_dir.dentry->d_inode->i_mutex);
@@ -168,7 +175,7 @@ out_unlock:
168 clp->cl_firststate = 1; 175 clp->cl_firststate = 1;
169 nfsd4_sync_rec_dir(); 176 nfsd4_sync_rec_dir();
170 } 177 }
171 nfs4_reset_user(uid, gid); 178 nfs4_reset_creds(original_cred);
172 dprintk("NFSD: nfsd4_create_clid_dir returns %d\n", status); 179 dprintk("NFSD: nfsd4_create_clid_dir returns %d\n", status);
173 return status; 180 return status;
174} 181}
@@ -211,20 +218,21 @@ nfsd4_build_dentrylist(void *arg, const char *name, int namlen,
211static int 218static int
212nfsd4_list_rec_dir(struct dentry *dir, recdir_func *f) 219nfsd4_list_rec_dir(struct dentry *dir, recdir_func *f)
213{ 220{
221 const struct cred *original_cred;
214 struct file *filp; 222 struct file *filp;
215 struct dentry_list_arg dla = { 223 struct dentry_list_arg dla = {
216 .parent = dir, 224 .parent = dir,
217 }; 225 };
218 struct list_head *dentries = &dla.dentries; 226 struct list_head *dentries = &dla.dentries;
219 struct dentry_list *child; 227 struct dentry_list *child;
220 uid_t uid;
221 gid_t gid;
222 int status; 228 int status;
223 229
224 if (!rec_dir_init) 230 if (!rec_dir_init)
225 return 0; 231 return 0;
226 232
227 nfs4_save_user(&uid, &gid); 233 status = nfs4_save_creds(&original_cred);
234 if (status < 0)
235 return status;
228 236
229 filp = dentry_open(dget(dir), mntget(rec_dir.mnt), O_RDONLY, 237 filp = dentry_open(dget(dir), mntget(rec_dir.mnt), O_RDONLY,
230 current_cred()); 238 current_cred());
@@ -250,7 +258,7 @@ out:
250 dput(child->dentry); 258 dput(child->dentry);
251 kfree(child); 259 kfree(child);
252 } 260 }
253 nfs4_reset_user(uid, gid); 261 nfs4_reset_creds(original_cred);
254 return status; 262 return status;
255} 263}
256 264
@@ -312,8 +320,7 @@ out:
312void 320void
313nfsd4_remove_clid_dir(struct nfs4_client *clp) 321nfsd4_remove_clid_dir(struct nfs4_client *clp)
314{ 322{
315 uid_t uid; 323 const struct cred *original_cred;
316 gid_t gid;
317 int status; 324 int status;
318 325
319 if (!rec_dir_init || !clp->cl_firststate) 326 if (!rec_dir_init || !clp->cl_firststate)
@@ -323,9 +330,13 @@ nfsd4_remove_clid_dir(struct nfs4_client *clp)
323 if (status) 330 if (status)
324 goto out; 331 goto out;
325 clp->cl_firststate = 0; 332 clp->cl_firststate = 0;
326 nfs4_save_user(&uid, &gid); 333
334 status = nfs4_save_creds(&original_cred);
335 if (status < 0)
336 goto out;
337
327 status = nfsd4_unlink_clid_dir(clp->cl_recdir, HEXDIR_LEN-1); 338 status = nfsd4_unlink_clid_dir(clp->cl_recdir, HEXDIR_LEN-1);
328 nfs4_reset_user(uid, gid); 339 nfs4_reset_creds(original_cred);
329 if (status == 0) 340 if (status == 0)
330 nfsd4_sync_rec_dir(); 341 nfsd4_sync_rec_dir();
331 mnt_drop_write(rec_dir.mnt); 342 mnt_drop_write(rec_dir.mnt);
@@ -402,16 +413,21 @@ nfsd4_recdir_load(void) {
402void 413void
403nfsd4_init_recdir(char *rec_dirname) 414nfsd4_init_recdir(char *rec_dirname)
404{ 415{
405 uid_t uid = 0; 416 const struct cred *original_cred;
406 gid_t gid = 0; 417 int status;
407 int status;
408 418
409 printk("NFSD: Using %s as the NFSv4 state recovery directory\n", 419 printk("NFSD: Using %s as the NFSv4 state recovery directory\n",
410 rec_dirname); 420 rec_dirname);
411 421
412 BUG_ON(rec_dir_init); 422 BUG_ON(rec_dir_init);
413 423
414 nfs4_save_user(&uid, &gid); 424 status = nfs4_save_creds(&original_cred);
425 if (status < 0) {
426 printk("NFSD: Unable to change credentials to find recovery"
427 " directory: error %d\n",
428 status);
429 return;
430 }
415 431
416 status = kern_path(rec_dirname, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, 432 status = kern_path(rec_dirname, LOOKUP_FOLLOW | LOOKUP_DIRECTORY,
417 &rec_dir); 433 &rec_dir);
@@ -421,7 +437,7 @@ nfsd4_init_recdir(char *rec_dirname)
421 437
422 if (!status) 438 if (!status)
423 rec_dir_init = 1; 439 rec_dir_init = 1;
424 nfs4_reset_user(uid, gid); 440 nfs4_reset_creds(original_cred);
425} 441}
426 442
427void 443void