path: root/ipc
diff options
authorEric W. Biederman <>2018-03-23 00:29:57 -0500
committerEric W. Biederman <>2018-03-27 15:53:09 -0500
commit98f929b1bd4d0b7c7a77d0d9776d1b924db2e454 (patch)
tree9cfeab6782aea7b92f858b5e3e595b75fe22bfa3 /ipc
parent03f1fc09180b345582889a344b012d069b3a6dbe (diff)
ipc/shm: Fix shmctl(..., IPC_STAT, ...) between pid namespaces.
Today shm_cpid and shm_lpid are remembered in the pid namespace of the creator and the processes that last touched a sysvipc shared memory segment. If you have processes in multiple pid namespaces that is just wrong, and I don't know how this has been over-looked for so long. As only creation and shared memory attach and shared memory detach update the pids I do not expect there to be a repeat of the issues when struct pid was attached to each af_unix skb, which in some notable cases cut the performance in half. The problem was threads of the same process updating same struct pid from different cpus causing the cache line to be highly contended and bounce between cpus. As creation, attach, and detach are expected to be rare operations for sysvipc shared memory segments I do not expect that kind of cache line ping pong to cause probems. In addition because the pid is at a fixed location in the structure instead of being dynamic on a skb, the reference count of the pid does not need to be updated on each operation if the pid is the same. This ability to simply skip the pid reference count changes if the pid is unchanging further reduces the likelihood of the a cache line holding a pid reference count ping-ponging between cpus. Fixes: b488893a390e ("pid namespaces: changes to show virtual ids to user") Reviewed-by: Nagarathnam Muthusamy <> Signed-off-by: "Eric W. Biederman" <>
Diffstat (limited to 'ipc')
1 files changed, 15 insertions, 10 deletions
diff --git a/ipc/shm.c b/ipc/shm.c
index 0565669..932b7e4 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -57,8 +57,8 @@ struct shmid_kernel /* private to the kernel */
time64_t shm_atim;
time64_t shm_dtim;
time64_t shm_ctim;
- pid_t shm_cprid;
- pid_t shm_lprid;
+ struct pid *shm_cprid;
+ struct pid *shm_lprid;
struct user_struct *mlock_user;
/* The task created the shm object. NULL if the task is dead. */
@@ -226,7 +226,7 @@ static int __shm_open(struct vm_area_struct *vma)
return PTR_ERR(shp);
shp->shm_atim = ktime_get_real_seconds();
- shp->shm_lprid = task_tgid_vnr(current);
+ ipc_update_pid(&shp->shm_lprid, task_tgid(current));
return 0;
@@ -267,6 +267,8 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
+ ipc_update_pid(&shp->shm_cprid, NULL);
+ ipc_update_pid(&shp->shm_lprid, NULL);
ipc_rcu_putref(&shp->shm_perm, shm_rcu_free);
@@ -311,7 +313,7 @@ static void shm_close(struct vm_area_struct *vma)
if (WARN_ON_ONCE(IS_ERR(shp)))
goto done; /* no-op */
- shp->shm_lprid = task_tgid_vnr(current);
+ ipc_update_pid(&shp->shm_lprid, task_tgid(current));
shp->shm_dtim = ktime_get_real_seconds();
if (shm_may_destroy(ns, shp))
@@ -614,8 +616,8 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
if (IS_ERR(file))
goto no_file;
- shp->shm_cprid = task_tgid_vnr(current);
- shp->shm_lprid = 0;
+ shp->shm_cprid = get_pid(task_tgid(current));
+ shp->shm_lprid = NULL;
shp->shm_atim = shp->shm_dtim = 0;
shp->shm_ctim = ktime_get_real_seconds();
shp->shm_segsz = size;
@@ -648,6 +650,8 @@ no_id:
user_shm_unlock(size, shp->mlock_user);
+ ipc_update_pid(&shp->shm_cprid, NULL);
+ ipc_update_pid(&shp->shm_lprid, NULL);
call_rcu(&shp->shm_perm.rcu, shm_rcu_free);
return error;
@@ -970,8 +974,8 @@ static int shmctl_stat(struct ipc_namespace *ns, int shmid,
tbuf->shm_atime = shp->shm_atim;
tbuf->shm_dtime = shp->shm_dtim;
tbuf->shm_ctime = shp->shm_ctim;
- tbuf->shm_cpid = shp->shm_cprid;
- tbuf->shm_lpid = shp->shm_lprid;
+ tbuf->shm_cpid = pid_vnr(shp->shm_cprid);
+ tbuf->shm_lpid = pid_vnr(shp->shm_lprid);
tbuf->shm_nattch = shp->shm_nattch;
@@ -1605,6 +1609,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
+ struct pid_namespace *pid_ns = ipc_seq_pid_ns(s);
struct user_namespace *user_ns = seq_user_ns(s);
struct kern_ipc_perm *ipcp = it;
struct shmid_kernel *shp;
@@ -1627,8 +1632,8 @@ static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
- shp->shm_cprid,
- shp->shm_lprid,
+ pid_nr_ns(shp->shm_cprid, pid_ns),
+ pid_nr_ns(shp->shm_lprid, pid_ns),
from_kuid_munged(user_ns, shp->shm_perm.uid),
from_kgid_munged(user_ns, shp->shm_perm.gid),
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