From 118258f5c23cf881c8b88baf86b3be17daee4e0a Mon Sep 17 00:00:00 2001 From: "Bjoern A. Zeeb" Date: Wed, 3 Dec 2008 15:54:35 +0000 Subject: [PATCH] Fix a credential reference leak. [1] Close subtle but relatively unlikely race conditions when propagating the vnode write error to other active sessions tracing to the same vnode, without holding a reference on the vnode anymore. [2] PR: kern/126368 [1] Submitted by: rwatson [2] Reviewed by: kib, rwatson MFC after: 4 weeks --- sys/kern/kern_ktrace.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/sys/kern/kern_ktrace.c b/sys/kern/kern_ktrace.c index c8e44511d4a..f4304deabdb 100644 --- a/sys/kern/kern_ktrace.c +++ b/sys/kern/kern_ktrace.c @@ -907,12 +907,7 @@ ktr_writerequest(struct thread *td, struct ktr_request *req) */ mtx_lock(&ktrace_mtx); vp = td->td_proc->p_tracevp; - if (vp != NULL) - VREF(vp); cred = td->td_proc->p_tracecred; - if (cred != NULL) - crhold(cred); - mtx_unlock(&ktrace_mtx); /* * If vp is NULL, the vp has been cleared out from under this @@ -921,9 +916,13 @@ ktr_writerequest(struct thread *td, struct ktr_request *req) */ if (vp == NULL) { KASSERT(cred == NULL, ("ktr_writerequest: cred != NULL")); + mtx_unlock(&ktrace_mtx); return; } + VREF(vp); KASSERT(cred != NULL, ("ktr_writerequest: cred == NULL")); + crhold(cred); + mtx_unlock(&ktrace_mtx); kth = &req->ktr_header; datalen = data_lengths[(u_short)kth->ktr_type & ~KTR_DROP]; @@ -963,18 +962,26 @@ ktr_writerequest(struct thread *td, struct ktr_request *req) error = VOP_WRITE(vp, &auio, IO_UNIT | IO_APPEND, cred); VOP_UNLOCK(vp, 0); vn_finished_write(mp); - vrele(vp); - VFS_UNLOCK_GIANT(vfslocked); - if (!error) + crfree(cred); + if (!error) { + vrele(vp); + VFS_UNLOCK_GIANT(vfslocked); return; + } + VFS_UNLOCK_GIANT(vfslocked); + /* * If error encountered, give up tracing on this vnode. We defer * all the vrele()'s on the vnode until after we are finished walking * the various lists to avoid needlessly holding locks. + * NB: at this point we still hold the vnode reference that must + * not go away as we need the valid vnode to compare with. Thus let + * vrele_count start at 1 and the reference will be freed + * by the loop at the end after our last use of vp. */ log(LOG_NOTICE, "ktrace write failed, errno %d, tracing stopped\n", error); - vrele_count = 0; + vrele_count = 1; /* * First, clear this vnode from being used by any processes in the * system. -- 2.45.2