[PATCH 3.10 044/173] ipc/sem.c: synchronize semop and semctl with IPC_RMID

Greg Kroah-Hartman
2013-12-02T21:06:17Z

From: Manfred Spraul <manfred@colorfullife.com>

commit 6e224f94597842c5eb17f1fc2208d20b6f7f7d49 upstream.

After acquiring the semlock spinlock, 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 also:
- standardizes the tests for .deleted, so that all tests in one
function leave the function with the same approach.
- unconditionally tests for .deleted immediately after every call to
sem_lock - even it it means that for semctl(GETALL), .deleted will be
tested twice.

Both changes make the review simpler: After every sem_lock, there must
be a test of .deleted, followed by a goto to the cleanup code (if the
function uses "goto cleanup").

The only exception is semctl_down(): If sem_ids().rwsem is locked, then
the presence in ids->ipcs_idr is equivalent to !.deleted, thus no
additional test is required.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Mike Galbraith <efault@gmx.de>
Acked-by: Davidlohr Bueso <davidlohr@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
ipc/sem.c | 42 +++++++++++++++++++++++++++++-------------
1 file changed, 29 insertions(+), 13 deletions(-)

--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1282,6 +1282,12 @@ static int semctl_setval(struct ipc_name

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);
@@ -1336,12 +1342,14 @@ static int semctl_main(struct ipc_namesp
int i;

sem_lock(sma, NULL, -1);
+ if (sma->sem_perm.deleted) {
+ err = -EIDRM;
+ goto out_unlock;
+ }
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();
@@ -1354,10 +1362,8 @@ static int semctl_main(struct ipc_namesp
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 < sma->sem_nsems; i++)
@@ -1375,8 +1381,8 @@ static int semctl_main(struct ipc_namesp
struct sem_undo *un;

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

@@ -1404,10 +1410,8 @@ static int semctl_main(struct ipc_namesp
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++)
@@ -1431,6 +1435,10 @@ static int semctl_main(struct ipc_namesp
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) {
@@ -1836,6 +1844,10 @@ SYSCALL_DEFINE4(semtimedop, int, semid,
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
@@ -1843,8 +1855,6 @@ SYSCALL_DEFINE4(semtimedop, int, semid,
* 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;

@@ -2057,6 +2067,12 @@ 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