lkml.org 
[lkml]   [2013]   [Sep]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] ipc/sem.c: synchronize semop and semctl with IPC_RMID
Date
After acquiring the semlock spinlock, the operations must test that the
array is still valid.

- semctl() and exit_sem() would walk stale linked lists (ugly, but should
be ok: all lists are empty)

- semtimedop() would sleep forever - and if woken up due to a signal -
access memory after free.

The patch standardizes the tests for .deleted, so that all tests in one
function leave the function with the same approach.

Right now, it's a mixture of "goto cleanup", some cleanup and then
"goto further_cleanup" and all cleanup+"return -EIDRM" - that makes the
review much harder.

Davidlohr: Could you please review the patch?
I did some stress test, but probably I didn't hit exactly the modified
lines.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
---
ipc/sem.c | 43 ++++++++++++++++++++++++++++++-------------
1 file changed, 30 insertions(+), 13 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 19c8b98..a2fa795 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1229,6 +1229,12 @@ static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,

sem_lock(sma, NULL, -1);

+ if (sma->sem_perm.deleted) {
+ sem_unlock(sma, -1);
+ rcu_read_unlock();
+ return -EIDRM;
+ }
+
curr = &sma->sem_base[semnum];

ipc_assert_locked_object(&sma->sem_perm);
@@ -1285,10 +1291,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
sem_lock(sma, NULL, -1);
if(nsems > SEMMSL_FAST) {
if (!ipc_rcu_getref(sma)) {
- sem_unlock(sma, -1);
- rcu_read_unlock();
err = -EIDRM;
- goto out_free;
+ goto out_unlock;
}
sem_unlock(sma, -1);
rcu_read_unlock();
@@ -1301,10 +1305,13 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
rcu_read_lock();
sem_lock_and_putref(sma);
if (sma->sem_perm.deleted) {
- sem_unlock(sma, -1);
- rcu_read_unlock();
err = -EIDRM;
- goto out_free;
+ goto out_unlock;
+ }
+ } else {
+ if (sma->sem_perm.deleted) {
+ err = -EIDRM;
+ goto out_unlock;
}
}
for (i = 0; i < sma->sem_nsems; i++)
@@ -1322,8 +1329,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
struct sem_undo *un;

if (!ipc_rcu_getref(sma)) {
- rcu_read_unlock();
- return -EIDRM;
+ err = -EIDRM;
+ goto out_rcu_wakeup;
}
rcu_read_unlock();

@@ -1351,10 +1358,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
rcu_read_lock();
sem_lock_and_putref(sma);
if (sma->sem_perm.deleted) {
- sem_unlock(sma, -1);
- rcu_read_unlock();
err = -EIDRM;
- goto out_free;
+ goto out_unlock;
}

for (i = 0; i < nsems; i++)
@@ -1378,6 +1383,10 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
goto out_rcu_wakeup;

sem_lock(sma, NULL, -1);
+ if (sma->sem_perm.deleted) {
+ err = -EIDRM;
+ goto out_unlock;
+ }
curr = &sma->sem_base[semnum];

switch (cmd) {
@@ -1783,6 +1792,10 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
if (error)
goto out_rcu_wakeup;

+ error = -EIDRM;
+ locknum = sem_lock(sma, sops, nsops);
+ if (sma->sem_perm.deleted)
+ goto out_unlock_free;
/*
* semid identifiers are not unique - find_alloc_undo may have
* allocated an undo structure, it was invalidated by an RMID
@@ -1790,8 +1803,6 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
* This case can be detected checking un->semid. The existence of
* "un" itself is guaranteed by rcu.
*/
- error = -EIDRM;
- locknum = sem_lock(sma, sops, nsops);
if (un && un->semid == -1)
goto out_unlock_free;

@@ -1999,6 +2010,12 @@ void exit_sem(struct task_struct *tsk)
}

sem_lock(sma, NULL, -1);
+ /* exit_sem raced with IPC_RMID, nothing to do */
+ if (sma->sem_perm.deleted) {
+ sem_unlock(sma, -1);
+ rcu_read_unlock();
+ continue;
+ }
un = __lookup_undo(ulp, semid);
if (un == NULL) {
/* exit_sem raced with IPC_RMID+semget() that created
--
1.8.3.1


\
 
 \ /
  Last update: 2013-09-30 11:41    [W:0.917 / U:0.004 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site