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jail: Add safety around prison_deref() flags.

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do_jail_attach() now only uses the PD_XXX flags that refer to lock
status, so make sure that something else like PD_KILL doesn't slip
through.

Add a KASSERT() in prison_deref() to catch any further PD_KILL misuse.
This commit is contained in:
Jamie Gritton 2021-02-25 20:10:42 -08:00
parent 108a9384e9
commit 589e4c1df4
1 changed files with 8 additions and 2 deletions
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10
sys/kern/kern_jail.c
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@ -161,6 +161,8 @@ static void prison_racct_detach(struct prison *pr);
#define PD_LOCKED 0x10 /* pr_mtx is held */
#define PD_LIST_SLOCKED 0x20 /* allprison_lock is held shared */
#define PD_LIST_XLOCKED 0x40 /* allprison_lock is held exclusive */
#define PD_OP_FLAGS 0x07 /* Operation flags */
#define PD_LOCK_FLAGS 0x70 /* Lock status flags */
/*
* Parameter names corresponding to PR_* flag values. Size values are for kvm
@ -1836,7 +1838,7 @@ kern_jail_set(struct thread *td, struct uio *optuio, int flags)
/* Attach this process to the prison if requested. */
if (flags & JAIL_ATTACH) {
error = do_jail_attach(td, pr,
prison_lock_xlock(pr, drflags & ~PD_KILL));
prison_lock_xlock(pr, drflags & PD_LOCK_FLAGS));
drflags &= ~(PD_LOCKED | PD_LIST_XLOCKED);
if (error) {
vfs_opterror(opts, "attach failed");
@ -2346,6 +2348,7 @@ do_jail_attach(struct thread *td, struct prison *pr, int drflags)
mtx_assert(&pr->pr_mtx, MA_OWNED);
sx_assert(&allprison_lock, SX_LOCKED);
drflags &= PD_LOCK_FLAGS;
/*
* XXX: Note that there is a slight race here if two threads
* in the same privileged process attempt to attach to two
@ -2719,6 +2722,8 @@ prison_deref(struct prison *pr, int flags)
for (;;) {
if (flags & PD_KILL) {
/* Kill the prison and its descendents. */
KASSERT(pr != &prison0,
("prison_deref trying to kill prison0"));
if (!(flags & PD_DEREF)) {
prison_hold(pr);
flags |= PD_DEREF;
@ -2755,7 +2760,6 @@ prison_deref(struct prison *pr, int flags)
}
}
if (flags & PD_KILL) {
flags &= ~PD_KILL;
/*
* Any remaining user references are probably processes
* that need to be killed, either in this prison or its
@ -2763,6 +2767,8 @@ prison_deref(struct prison *pr, int flags)
*/
if (refcount_load(&pr->pr_uref) > 0)
killpr = pr;
/* Make sure the parent prison doesn't get killed. */
flags &= ~PD_KILL;
}
if (flags & PD_DEREF) {
/* Drop a reference. */