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ktrace: fix a race between writes and close

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It was possible that termination of ktrace session occured during some
record write, in which case write occured after the close of the vnode.
Use ktr_io_params refcounting to avoid this situation, by taking the
reference on the structure instead of vnode.

Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D30400
This commit is contained in:
Konstantin Belousov 2021-05-22 15:40:00 +03:00
parent 48235c377f
commit fc369a353b
1 changed files with 11 additions and 11 deletions
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22
sys/kern/kern_ktrace.c
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@ -1257,7 +1257,7 @@ ktrsetchildren(struct thread *td, struct proc *top, int ops, int facs,
static void
ktr_writerequest(struct thread *td, struct ktr_request *req)
{
struct ktr_io_params *kiop;
struct ktr_io_params *kiop, *kiop1;
struct ktr_header *kth;
struct vnode *vp;
struct proc *p;
@ -1272,14 +1272,10 @@ ktr_writerequest(struct thread *td, struct ktr_request *req)
p = td->td_proc;
/*
* We hold the vnode and credential for use in I/O in case ktrace is
* We reference the kiop for use in I/O in case ktrace is
* disabled on the process as we write out the request.
*
* XXXRW: This is not ideal: we could end up performing a write after
* the vnode has been closed.
*/
mtx_lock(&ktrace_mtx);
kiop = p->p_ktrioparms;
/*
@ -1291,13 +1287,12 @@ ktr_writerequest(struct thread *td, struct ktr_request *req)
return;
}
ktr_io_params_ref(kiop);
vp = kiop->vp;
cred = kiop->cr;
lim = kiop->lim;
vrefact(vp);
KASSERT(cred != NULL, ("ktr_writerequest: cred == NULL"));
crhold(cred);
mtx_unlock(&ktrace_mtx);
kth = &req->ktr_header;
@ -1339,9 +1334,11 @@ ktr_writerequest(struct thread *td, struct ktr_request *req)
error = VOP_WRITE(vp, &auio, IO_UNIT | IO_APPEND, cred);
VOP_UNLOCK(vp);
vn_finished_write(mp);
crfree(cred);
if (error == 0) {
vrele(vp);
mtx_lock(&ktrace_mtx);
kiop = ktr_io_params_rele(kiop);
mtx_unlock(&ktrace_mtx);
ktr_io_params_free(kiop);
return;
}
@ -1354,12 +1351,15 @@ ktr_writerequest(struct thread *td, struct ktr_request *req)
"ktrace write failed, errno %d, tracing stopped for pid %d\n",
error, p->p_pid);
kiop1 = NULL;
PROC_LOCK(p);
mtx_lock(&ktrace_mtx);
if (p->p_ktrioparms != NULL && p->p_ktrioparms->vp == vp)
kiop = ktr_freeproc(p);
kiop1 = ktr_freeproc(p);
kiop = ktr_io_params_rele(kiop);
mtx_unlock(&ktrace_mtx);
PROC_UNLOCK(p);
ktr_io_params_free(kiop1);
ktr_io_params_free(kiop);
vrele(vp);
}