[PATCH 6/9] ARM: oabi-compat: rework sys_semtimedop emulation

Arnd Bergmann
2020-09-07T15:45:25Z

sys_oabi_semtimedop() is one of the last users of set_fs() on Arm. To
remove this one, expose the internal code of the actual implementation
that operates on a kernel pointer and call it directly after copying.

There should be no measurable impact on the normal execution of this
function, and it makes the overly long function a little shorter, which
may help readability.

While reworking the oabi version, make it behave a little more like
the native one, using kvmalloc_array() and restructure the code
flow in a similar way.

The naming of __do_semtimedop() is not very good, I hope someone can
come up with a better name.

One regression was spotted by kernel test robot <rong.a.chen@intel.com>
and fixed before the first mailing list submission.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
arch/arm/kernel/sys_oabi-compat.c | 38 ++++++++------
include/linux/syscalls.h | 2 +
ipc/sem.c | 84 +++++++++++++++++++------------
3 files changed, 76 insertions(+), 48 deletions(-)

diff --git a/arch/arm/kernel/sys_oabi-compat.c b/arch/arm/kernel/sys_oabi-compat.c
index abf1153c5315..d3c6460d13ca 100644
--- a/arch/arm/kernel/sys_oabi-compat.c
+++ b/arch/arm/kernel/sys_oabi-compat.c
@@ -80,6 +80,7 @@
#include <linux/socket.h>
#include <linux/net.h>
#include <linux/ipc.h>
+#include <linux/ipc_namespace.h>
#include <linux/uaccess.h>
#include <linux/slab.h>

@@ -293,46 +294,51 @@ struct oabi_sembuf {
unsigned short __pad;
};

+#define sc_semopm sem_ctls[2]
+
asmlinkage long sys_oabi_semtimedop(int semid,
struct oabi_sembuf __user *tsops,
unsigned nsops,
const struct old_timespec32 __user *timeout)
{
+ struct ipc_namespace *ns;
struct sembuf *sops;
- struct old_timespec32 local_timeout;
long err;
int i;

+ ns = current->nsproxy->ipc_ns;
+ if (nsops > ns->sc_semopm)
+ return -E2BIG;
if (nsops < 1 || nsops > SEMOPM)
return -EINVAL;
- if (!access_ok(tsops, sizeof(*tsops) * nsops))
- return -EFAULT;
- sops = kmalloc_array(nsops, sizeof(*sops), GFP_KERNEL);
+ sops = kvmalloc_array(nsops, sizeof(*sops), GFP_KERNEL);
if (!sops)
return -ENOMEM;
err = 0;
for (i = 0; i < nsops; i++) {
struct oabi_sembuf osb;
- err |= __copy_from_user(&osb, tsops, sizeof(osb));
+ err |= copy_from_user(&osb, tsops, sizeof(osb));
sops[i].sem_num = osb.sem_num;
sops[i].sem_op = osb.sem_op;
sops[i].sem_flg = osb.sem_flg;
tsops++;
}
- if (timeout) {
- /* copy this as well before changing domain protection */
- err |= copy_from_user(&local_timeout, timeout, sizeof(*timeout));
- timeout = &local_timeout;
- }
if (err) {
err = -EFAULT;
- } else {
- mm_segment_t fs = get_fs();
- set_fs(KERNEL_DS);
- err = sys_semtimedop_time32(semid, sops, nsops, timeout);
- set_fs(fs);
+ goto out;
+ }
+
+ if (timeout) {
+ struct timespec64 ts;
+ err = get_old_timespec32(&ts, timeout);
+ if (err)
+ goto out;
+ err = __do_semtimedop(semid, sops, nsops, &ts, ns);
+ goto out;
}
- kfree(sops);
+ err = __do_semtimedop(semid, sops, nsops, NULL, ns);
+out:
+ kvfree(sops);
return err;
}

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 75ac7f8ae93c..c77bd4cce536 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1340,6 +1340,8 @@ long ksys_old_shmctl(int shmid, int cmd, struct shmid_ds __user *buf);
long compat_ksys_semtimedop(int semid, struct sembuf __user *tsems,
unsigned int nsops,
const struct old_timespec32 __user *timeout);
+long __do_semtimedop(int semid, struct sembuf *tsems, unsigned int nsops,
+ const struct timespec64 *timeout, struct ipc_namespace *ns);

int __sys_getsockopt(int fd, int level, int optname, char __user *optval,
int __user *optlen);
diff --git a/ipc/sem.c b/ipc/sem.c
index 8c0244e0365e..515a39a67534 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1978,46 +1978,34 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
return un;
}

-static long do_semtimedop(int semid, struct sembuf __user *tsops,
- unsigned nsops, const struct timespec64 *timeout)
+long __do_semtimedop(int semid, struct sembuf *sops,
+ unsigned nsops, const struct timespec64 *timeout,
+ struct ipc_namespace *ns)
{
int error = -EINVAL;
struct sem_array *sma;
- struct sembuf fast_sops[SEMOPM_FAST];
- struct sembuf *sops = fast_sops, *sop;
+ struct sembuf *sop;
struct sem_undo *un;
int max, locknum;
bool undos = false, alter = false, dupsop = false;
struct sem_queue queue;
unsigned long dup = 0, jiffies_left = 0;
- struct ipc_namespace *ns;
-
- ns = current->nsproxy->ipc_ns;

if (nsops < 1 || semid < 0)
return -EINVAL;
if (nsops > ns->sc_semopm)
return -E2BIG;
- if (nsops > SEMOPM_FAST) {
- sops = kvmalloc_array(nsops, sizeof(*sops), GFP_KERNEL);
- if (sops == NULL)
- return -ENOMEM;
- }
-
- if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
- error = -EFAULT;
- goto out_free;
- }

if (timeout) {
if (timeout->tv_sec < 0 || timeout->tv_nsec < 0 ||
timeout->tv_nsec >= 1000000000L) {
error = -EINVAL;
- goto out_free;
+ goto out;
}
jiffies_left = timespec64_to_jiffies(timeout);
}

+
max = 0;
for (sop = sops; sop < sops + nsops; sop++) {
unsigned long mask = 1ULL << ((sop->sem_num) % BITS_PER_LONG);
@@ -2046,7 +2034,7 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,
un = find_alloc_undo(ns, semid);
if (IS_ERR(un)) {
error = PTR_ERR(un);
- goto out_free;
+ goto out;
}
} else {
un = NULL;
@@ -2057,25 +2045,25 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,
if (IS_ERR(sma)) {
rcu_read_unlock();
error = PTR_ERR(sma);
- goto out_free;
+ goto out;
}

error = -EFBIG;
if (max >= sma->sem_nsems) {
rcu_read_unlock();
- goto out_free;
+ goto out;
}

error = -EACCES;
if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO)) {
rcu_read_unlock();
- goto out_free;
+ goto out;
}

error = security_sem_semop(&sma->sem_perm, sops, nsops, alter);
if (error) {
rcu_read_unlock();
- goto out_free;
+ goto out;
}

error = -EIDRM;
@@ -2089,7 +2077,7 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,
* entangled here and why it's RMID race safe on comments at sem_lock()
*/
if (!ipc_valid_object(&sma->sem_perm))
- goto out_unlock_free;
+ goto out_unlock;
/*
* semid identifiers are not unique - find_alloc_undo may have
* allocated an undo structure, it was invalidated by an RMID
@@ -2098,7 +2086,7 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,
* "un" itself is guaranteed by rcu.
*/
if (un && un->semid == -1)
- goto out_unlock_free;
+ goto out_unlock;

queue.sops = sops;
queue.nsops = nsops;
@@ -2124,10 +2112,10 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,
rcu_read_unlock();
wake_up_q(&wake_q);

- goto out_free;
+ goto out;
}
if (error < 0) /* non-blocking error path */
- goto out_unlock_free;
+ goto out_unlock;

/*
* We need to sleep on this operation, so we put the current
@@ -2192,14 +2180,14 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,
if (error != -EINTR) {
/* see SEM_BARRIER_2 for purpose/pairing */
smp_acquire__after_ctrl_dep();
- goto out_free;
+ goto out;
}

rcu_read_lock();
locknum = sem_lock(sma, sops, nsops);

if (!ipc_valid_object(&sma->sem_perm))
- goto out_unlock_free;
+ goto out_unlock;

/*
* No necessity for any barrier: We are protect by sem_lock()
@@ -2211,7 +2199,7 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,
* Leave without unlink_queue(), but with sem_unlock().
*/
if (error != -EINTR)
- goto out_unlock_free;
+ goto out_unlock;

/*
* If an interrupt occurred we have to clean up the queue.
@@ -2222,13 +2210,45 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,

unlink_queue(sma, &queue);

-out_unlock_free:
+out_unlock:
sem_unlock(sma, locknum);
rcu_read_unlock();
+out:
+ return error;
+}
+
+static long do_semtimedop(int semid, struct sembuf __user *tsops,
+ unsigned nsops, const struct timespec64 *timeout)
+{
+ struct sembuf fast_sops[SEMOPM_FAST];
+ struct sembuf *sops = fast_sops;
+ struct ipc_namespace *ns;
+ int ret;
+
+ ns = current->nsproxy->ipc_ns;
+ if (nsops > ns->sc_semopm)
+ return -E2BIG;
+ if (nsops < 1)
+ return -EINVAL;
+
+ if (nsops > SEMOPM_FAST) {
+ sops = kvmalloc_array(nsops, sizeof(*sops), GFP_KERNEL);
+ if (sops == NULL)
+ return -ENOMEM;
+ }
+
+ if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
+ ret = -EFAULT;
+ goto out_free;
+ }
+
+ ret = __do_semtimedop(semid, sops, nsops, timeout, ns);
+
out_free:
if (sops != fast_sops)
kvfree(sops);
- return error;
+
+ return ret;
}

long ksys_semtimedop(int semid, struct sembuf __user *tsops,
--
2.27.0