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authorChristoph Lameter <cl@linux.com>2012-03-21 16:34:06 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-21 17:54:58 -0700
commit3268c63eded4612a3d07b56d1e02ce7731e6608e (patch)
treec8a07eb4cdf2697d610bb86d23eb46b0a5f892c2 /mm/mempolicy.c
parent385de35722c9a22917e7bc5e63cd83a8cffa5ecd (diff)
downloadlinux-3268c63eded4612a3d07b56d1e02ce7731e6608e.tar.gz
mm: fix move/migrate_pages() race on task struct
Migration functions perform the rcu_read_unlock too early. As a result the task pointed to may change from under us. This can result in an oops, as reported by Dave Hansen in https://lkml.org/lkml/2012/2/23/302. The following patch extend the period of the rcu_read_lock until after the permissions checks are done. We also take a refcount so that the task reference is stable when calling security check functions and performing cpuset node validation (which takes a mutex). The refcount is dropped before actual page migration occurs so there is no change to the refcounts held during page migration. Also move the determination of the mm of the task struct to immediately before the do_migrate*() calls so that it is clear that we switch from handling the task during permission checks to the mm for the actual migration. Since the determination is only done once and we then no longer use the task_struct we can be sure that we operate on a specific address space that will not change from under us. [akpm@linux-foundation.org: checkpatch fixes] Signed-off-by: Christoph Lameter <cl@linux.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Reported-by: Dave Hansen <dave@linux.vnet.ibm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mempolicy.c')
-rw-r--r--mm/mempolicy.c32
1 files changed, 19 insertions, 13 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 0a375706763..71e1a523e20 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1323,12 +1323,9 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
err = -ESRCH;
goto out;
}
- mm = get_task_mm(task);
- rcu_read_unlock();
+ get_task_struct(task);
err = -EINVAL;
- if (!mm)
- goto out;
/*
* Check if this process has the right to modify the specified
@@ -1336,14 +1333,13 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
* capabilities, superuser privileges or the same
* userid as the target process.
*/
- rcu_read_lock();
tcred = __task_cred(task);
if (cred->euid != tcred->suid && cred->euid != tcred->uid &&
cred->uid != tcred->suid && cred->uid != tcred->uid &&
!capable(CAP_SYS_NICE)) {
rcu_read_unlock();
err = -EPERM;
- goto out;
+ goto out_put;
}
rcu_read_unlock();
@@ -1351,26 +1347,36 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
/* Is the user allowed to access the target nodes? */
if (!nodes_subset(*new, task_nodes) && !capable(CAP_SYS_NICE)) {
err = -EPERM;
- goto out;
+ goto out_put;
}
if (!nodes_subset(*new, node_states[N_HIGH_MEMORY])) {
err = -EINVAL;
- goto out;
+ goto out_put;
}
err = security_task_movememory(task);
if (err)
- goto out;
+ goto out_put;
- err = do_migrate_pages(mm, old, new,
- capable(CAP_SYS_NICE) ? MPOL_MF_MOVE_ALL : MPOL_MF_MOVE);
-out:
+ mm = get_task_mm(task);
+ put_task_struct(task);
if (mm)
- mmput(mm);
+ err = do_migrate_pages(mm, old, new,
+ capable(CAP_SYS_NICE) ? MPOL_MF_MOVE_ALL : MPOL_MF_MOVE);
+ else
+ err = -EINVAL;
+
+ mmput(mm);
+out:
NODEMASK_SCRATCH_FREE(scratch);
return err;
+
+out_put:
+ put_task_struct(task);
+ goto out;
+
}