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cgroupfs: Fix lock ordering between kernfs.Filesystem.mu and TaskSet.mu.

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We can't DecRef a cgroup with TaskSet.mu held as it leads to circular
locking. Restructure task creation to drop cgroup refs outside the
TaskSet.mu critical section.

Reported-by: syzbot+16a334ab1d6873db18f2@syzkaller.appspotmail.com
Reported-by: syzbot+fe1b962d430d1170e671@syzkaller.appspotmail.com
PiperOrigin-RevId: 492589548
This commit is contained in:
Rahat Mahmood
2022-12-02 16:45:40 -08:00
committed by gVisor bot
parent 9c5cd1cfca
commit d0ae59368d
1 changed files with 12 additions and 15 deletions
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pkg/sentry/kernel/task_start.go
+12 -15
View File
@@ -19,7 +19,6 @@ import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/atomicbitops"
"gvisor.dev/gvisor/pkg/cleanup"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/hostarch"
@@ -177,11 +176,9 @@ func (ts *TaskSet) newTask(ctx context.Context, cfg *TaskConfig) (*Task, error)
// for justification.
var (
cg Cgroup
charged bool
cu cleanup.Cleanup
cg Cgroup
charged, committed bool
)
defer cu.Clean()
// Reserve cgroup PIDs controller charge. This is either commited when the
// new task enters the cgroup below, or rolled back on failure.
@@ -196,12 +193,16 @@ func (ts *TaskSet) newTask(ctx context.Context, cfg *TaskConfig) (*Task, error)
return nil, err
}
if charged {
cu.Add(func() {
if err := cg.Charge(t, cg.Dentry, CgroupControllerPIDs, CgroupResourcePID, -1); err != nil {
panic(fmt.Sprintf("Failed to clean up PIDs charge on task creation failure: %v", err))
defer func() {
if !committed {
if err := cg.Charge(t, cg.Dentry, CgroupControllerPIDs, CgroupResourcePID, -1); err != nil {
panic(fmt.Sprintf("Failed to clean up PIDs charge on task creation failure: %v", err))
}
}
cg.DecRef(ctx) // Ref from ChargeFor.
})
// Ref from ChargeFor. Note that we need to drop this outside of
// TaskSet.mu critical sections.
cg.DecRef(ctx)
}()
}
}
@@ -238,11 +239,7 @@ func (ts *TaskSet) newTask(ctx context.Context, cfg *TaskConfig) (*Task, error)
// srcT may be nil, in which case we default to root cgroups.
t.EnterInitialCgroups(srcT)
cu.Release()
if charged {
cg.decRef() // Ref from ChargeFor.
}
committed = true
if tg.leader == nil {
// New thread group.