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Date: Wed, 16 Apr 2008 23:45:56 +0200 (CEST)
From: Jesper Juhl <jesper.juhl@...il.com>
To: Ingo Molnar <mingo@...e.hu>
cc: linux-kernel@...r.kernel.org, Jesper Juhl <jesper.juhl@...il.com>
Subject: Possible mem leak in copy_process()
Hi Ingo,
I was just browsing through Coverity Scan results for the kernel and
noticed one thing it spotted that looks valid but which I have no idea how
to fix.
The code is, as far as I can see, written by you so I thought I'd forward
the info from Coverity to you in the hope that perhaps you'd know what to
do about it :-)
It's a memory leak in copy_process() - this is what coverity reports :
1004 static struct task_struct *copy_process(unsigned long clone_flags,
1005 unsigned long stack_start,
1006 struct pt_regs *regs,
1007 unsigned long stack_size,
1008 int __user *child_tidptr,
1009 struct pid *pid)
1010 {
<...snip...>
1198 retval = -ENOMEM;
Event alloc_fn: Called allocation function "alloc_pid" [model]
Event var_assign: Assigned variable "pid" to storage returned from "alloc_pid"
Also see events: [var_assign][leaked_storage][pass_arg]
1199 pid = alloc_pid(task_active_pid_ns(p));
At conditional (1): "pid == 0" taking false path
1200 if (!pid)
1201 goto bad_fork_cleanup_io;
1202
At conditional (2): "clone_flags & 536870912 != 0" taking true path
1203 if (clone_flags & CLONE_NEWPID) {
1204 retval = pid_ns_prepare_proc(task_active_pid_ns(p));
At conditional (3): "retval < 0" taking false path
1205 if (retval < 0)
1206 goto bad_fork_free_pid;
1207 }
1208 }
1209
Event pass_arg: Variable "pid" not freed or pointed-to in function "pid_nr" [model]
Also see events: [alloc_fn][var_assign][leaked_storage]
1210 p->pid = pid_nr(pid);
1211 p->tgid = p->pid;
At conditional (4): "clone_flags & 65536 != 0" taking true path
1212 if (clone_flags & CLONE_THREAD)
1213 p->tgid = current->tgid;
1214
At conditional (5): "clone_flags & 16777216 != 0" taking true path
1215 p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1216 /*
1217 * Clear TID on mm_release()?
1218 */
At conditional (6): "clone_flags & 2097152 != 0" taking true path
1219 p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
1220 #ifdef CONFIG_FUTEX
1221 p->robust_list = NULL;
1222 #ifdef CONFIG_COMPAT
1223 p->compat_robust_list = NULL;
1224 #endif
1225 INIT_LIST_HEAD(&p->pi_state_list);
1226 p->pi_state_cache = NULL;
1227 #endif
1228 /*
1229 * sigaltstack should be cleared when sharing the same VM
1230 */
At conditional (7): "clone_flags & 16640 == 256" taking true path
1231 if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1232 p->sas_ss_sp = p->sas_ss_size = 0;
1233
1234 /*
1235 * Syscall tracing should be turned off in the child regardless
1236 * of CLONE_PTRACE.
1237 */
1238 clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1239 #ifdef TIF_SYSCALL_EMU
1240 clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1241 #endif
1242 clear_all_latency_tracing(p);
1243
1244 /* Our parent execution domain becomes current domain
1245 These must match for thread signalling to apply */
1246 p->parent_exec_id = p->self_exec_id;
1247
1248 /* ok, now we should be set up.. */
At conditional (8): "clone_flags & 65536 != 0" taking true path
1249 p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
1250 p->pdeath_signal = 0;
1251 p->exit_state = 0;
1252
1253 /*
1254 * Ok, make it visible to the rest of the system.
1255 * We dont wake it up yet.
1256 */
1257 p->group_leader = p;
1258 INIT_LIST_HEAD(&p->thread_group);
1259 INIT_LIST_HEAD(&p->ptrace_children);
1260 INIT_LIST_HEAD(&p->ptrace_list);
1261
1262 /* Now that the task is set up, run cgroup callbacks if
1263 * necessary. We need to run them before the task is visible
1264 * on the tasklist. */
1265 cgroup_fork_callbacks(p);
1266 cgroup_callbacks_done = 1;
1267
1268 /* Need tasklist lock for parent etc handling! */
1269 write_lock_irq(&tasklist_lock);
1270
1271 /*
1272 * The task hasn't been attached yet, so its cpus_allowed mask will
1273 * not be changed, nor will its assigned CPU.
1274 *
1275 * The cpus_allowed mask of the parent may have changed after it was
1276 * copied first time - so re-copy it here, then check the child's CPU
1277 * to ensure it is on a valid CPU (and if not, just force it back to
1278 * parent's CPU). This avoids alot of nasty races.
1279 */
1280 p->cpus_allowed = current->cpus_allowed;
1281 p->rt.nr_cpus_allowed = current->rt.nr_cpus_allowed;
At conditional (9): "0" taking false path
At conditional (10): "((0) ? constant_test_bit : (variable_test_bit)) == 0" taking true path
1282 if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed) ||
1283 !cpu_online(task_cpu(p))))
At conditional (11): "4 == 4" taking true path
1284 set_task_cpu(p, smp_processor_id());
1285
1286 /* CLONE_PARENT re-uses the old parent */
At conditional (12): "clone_flags & 98304 != 0" taking true path
1287 if (clone_flags & (CLONE_PARENT|CLONE_THREAD))
1288 p->real_parent = current->real_parent;
1289 else
1290 p->real_parent = current;
1291 p->parent = p->real_parent;
1292
1293 spin_lock(¤t->sighand->siglock);
1294
1295 /*
1296 * Process group and session signals need to be delivered to just the
1297 * parent before the fork or both the parent and the child after the
1298 * fork. Restart if a signal comes in before we add the new process to
1299 * it's process group.
1300 * A fatal signal pending means that current will exit, so the new
1301 * thread can't slip out of an OOM kill (or normal SIGKILL).
1302 */
1303 recalc_sigpending();
At conditional (13): "signal_pending != 0" taking false path
1304 if (signal_pending(current)) {
1305 spin_unlock(¤t->sighand->siglock);
1306 write_unlock_irq(&tasklist_lock);
1307 retval = -ERESTARTNOINTR;
1308 goto bad_fork_free_pid;
1309 }
1310
At conditional (14): "clone_flags & 65536 != 0" taking true path
1311 if (clone_flags & CLONE_THREAD) {
1312 p->group_leader = current->group_leader;
1313 list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1314
At conditional (15): "((get_current)->signal)->it_virt_expires != 0"
taking true path
1315 if (!cputime_eq(current->signal->it_virt_expires,
1316 cputime_zero) ||
1317 !cputime_eq(current->signal->it_prof_expires,
1318 cputime_zero) ||
1319 current->signal->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY ||
1320 !list_empty(¤t->signal->cpu_timers[0]) ||
1321 !list_empty(¤t->signal->cpu_timers[1]) ||
1322 !list_empty(¤t->signal->cpu_timers[2])) {
1323 /*
1324 * Have child wake up on its first tick to check
1325 * for process CPU timers.
1326 */
1327 p->it_prof_expires = jiffies_to_cputime(1);
1328 }
1329 }
1330
At conditional (16): "(p)->pid != 0" taking false path
1331 if (likely(p->pid)) {
1332 add_parent(p);
1333 if (unlikely(p->ptrace & PT_PTRACED))
1334 __ptrace_link(p, current->parent);
1335
1336 if (thread_group_leader(p)) {
1337 if (clone_flags & CLONE_NEWPID)
1338 p->nsproxy->pid_ns->child_reaper = p;
1339
1340 p->signal->leader_pid = pid;
1341 p->signal->tty = current->signal->tty;
1342 set_task_pgrp(p, task_pgrp_nr(current));
1343 set_task_session(p, task_session_nr(current));
1344 attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1345 attach_pid(p, PIDTYPE_SID, task_session(current));
1346 list_add_tail_rcu(&p->tasks, &init_task.tasks);
1347 __get_cpu_var(process_counts)++;
1348 }
1349 attach_pid(p, PIDTYPE_PID, pid);
1350 nr_threads++;
1351 }
1352
1353 total_forks++;
1354 spin_unlock(¤t->sighand->siglock);
1355 write_unlock_irq(&tasklist_lock);
1356 proc_fork_connector(p);
1357 cgroup_post_fork(p);
Event leaked_storage: Returned without freeing storage "pid"
Also see events: [alloc_fn][var_assign][pass_arg]
1358 return p;
Perhaps it can never happen the way Coverity thinks it can. You are a much
better judge of that than I, but it looks to me like it's at least
possible in theory - in which case we have a potential leak every time we
create a new process and that can't be good...
Anyway, just wanted to bring it to your attention. Bye bye :-)
--
Jesper Juhl < jesper.juhl@...il.com>
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