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Bruce Fields" To: Doug Nazar Cc: "Kraus, Sebastian" , "linux-nfs@vger.kernel.org" , Steve Dickson , Olga Kornievskaia Subject: Re: [PATCH v2] Re: Strange segmentation violations of rpc.gssd in Debian Buster Message-ID: <20200626214401.GE11850@fieldses.org> References: <5c45562c90404838944ee71a1d926c74@tu-berlin.de> <20200622223628.GC11051@fieldses.org> <406fe972135846dc8a23b60be59b0590@tu-berlin.de> <1527b158-3404-168c-8908-de4b8a709ccd@nazar.ca> <20200626194622.GB11850@fieldses.org> <3eb80b1f-e4d3-e87c-aacd-34dc28637948@nazar.ca> <20200626210243.GD11850@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Fri, Jun 26, 2020 at 05:30:15PM -0400, Doug Nazar wrote: > On 2020-06-26 17:02, J. Bruce Fields wrote: > >Unless I'm missing something--an upcall thread could still be using this > >file descriptor. > > > >If we're particularly unlucky, we could do a new open in a moment and > >reuse this file descriptor number, and then then writes in do_downcall() > >could end up going to some other random file. > > > >I think we want these closes done by gssd_free_client() in the !refcnt > >case? > > Makes sense. I was thinking more that it was an abort situation and > we shouldn't be sending any data to the kernel but re-use is > definitely a concern. > > I've split it so that we are removed from the event loop in > destroy() but the close happens in free(). Looks good to me. Steve? --b. > > Doug > > From 8ef49081e8a42bfa05bb63265cd4f951e2b23413 Mon Sep 17 00:00:00 2001 > From: Doug Nazar > Date: Fri, 26 Jun 2020 16:02:04 -0400 > Subject: [PATCH] gssd: Refcount struct clnt_info to protect multithread usage > > Struct clnt_info is shared with the various upcall threads so > we need to ensure that it stays around even if the client dir > gets removed. > > Reported-by: Sebastian Kraus > Signed-off-by: Doug Nazar > --- > utils/gssd/gssd.c | 67 ++++++++++++++++++++++++++++++++---------- > utils/gssd/gssd.h | 5 ++-- > utils/gssd/gssd_proc.c | 4 +-- > 3 files changed, 55 insertions(+), 21 deletions(-) > > diff --git a/utils/gssd/gssd.c b/utils/gssd/gssd.c > index 588da0fb..b40c3220 100644 > --- a/utils/gssd/gssd.c > +++ b/utils/gssd/gssd.c > @@ -90,9 +90,7 @@ char *ccachedir = NULL; > /* Avoid DNS reverse lookups on server names */ > static bool avoid_dns = true; > static bool use_gssproxy = false; > -int thread_started = false; > -pthread_mutex_t pmutex = PTHREAD_MUTEX_INITIALIZER; > -pthread_cond_t pcond = PTHREAD_COND_INITIALIZER; > +pthread_mutex_t clp_lock = PTHREAD_MUTEX_INITIALIZER; > > TAILQ_HEAD(topdir_list_head, topdir) topdir_list; > > @@ -359,20 +357,28 @@ out: > free(port); > } > > +/* Actually frees clp and fields that might be used from other > + * threads if was last reference. > + */ > static void > -gssd_destroy_client(struct clnt_info *clp) > +gssd_free_client(struct clnt_info *clp) > { > - if (clp->krb5_fd >= 0) { > + int refcnt; > + > + pthread_mutex_lock(&clp_lock); > + refcnt = --clp->refcount; > + pthread_mutex_unlock(&clp_lock); > + if (refcnt > 0) > + return; > + > + printerr(3, "freeing client %s\n", clp->relpath); > + > + if (clp->krb5_fd >= 0) > close(clp->krb5_fd); > - event_del(&clp->krb5_ev); > - } > > - if (clp->gssd_fd >= 0) { > + if (clp->gssd_fd >= 0) > close(clp->gssd_fd); > - event_del(&clp->gssd_ev); > - } > > - inotify_rm_watch(inotify_fd, clp->wd); > free(clp->relpath); > free(clp->servicename); > free(clp->servername); > @@ -380,6 +386,24 @@ gssd_destroy_client(struct clnt_info *clp) > free(clp); > } > > +/* Called when removing from clnt_list to tear down event handling. > + * Will then free clp if was last reference. > + */ > +static void > +gssd_destroy_client(struct clnt_info *clp) > +{ > + printerr(3, "destroying client %s\n", clp->relpath); > + > + if (clp->krb5_fd >= 0) > + event_del(&clp->krb5_ev); > + > + if (clp->gssd_fd >= 0) > + event_del(&clp->gssd_ev); > + > + inotify_rm_watch(inotify_fd, clp->wd); > + gssd_free_client(clp); > +} > + > static void gssd_scan(void); > > static int > @@ -416,11 +440,21 @@ static struct clnt_upcall_info *alloc_upcall_info(struct clnt_info *clp) > info = malloc(sizeof(struct clnt_upcall_info)); > if (info == NULL) > return NULL; > + > + pthread_mutex_lock(&clp_lock); > + clp->refcount++; > + pthread_mutex_unlock(&clp_lock); > info->clp = clp; > > return info; > } > > +void free_upcall_info(struct clnt_upcall_info *info) > +{ > + gssd_free_client(info->clp); > + free(info); > +} > + > /* For each upcall read the upcall info into the buffer, then create a > * thread in a detached state so that resources are released back into > * the system without the need for a join. > @@ -438,13 +472,13 @@ gssd_clnt_gssd_cb(int UNUSED(fd), short UNUSED(which), void *data) > info->lbuflen = read(clp->gssd_fd, info->lbuf, sizeof(info->lbuf)); > if (info->lbuflen <= 0 || info->lbuf[info->lbuflen-1] != '\n') { > printerr(0, "WARNING: %s: failed reading request\n", __func__); > - free(info); > + free_upcall_info(info); > return; > } > info->lbuf[info->lbuflen-1] = 0; > > if (start_upcall_thread(handle_gssd_upcall, info)) > - free(info); > + free_upcall_info(info); > } > > static void > @@ -461,12 +495,12 @@ gssd_clnt_krb5_cb(int UNUSED(fd), short UNUSED(which), void *data) > sizeof(info->uid)) < (ssize_t)sizeof(info->uid)) { > printerr(0, "WARNING: %s: failed reading uid from krb5 " > "upcall pipe: %s\n", __func__, strerror(errno)); > - free(info); > + free_upcall_info(info); > return; > } > > if (start_upcall_thread(handle_krb5_upcall, info)) > - free(info); > + free_upcall_info(info); > } > > static struct clnt_info * > @@ -501,6 +535,7 @@ gssd_get_clnt(struct topdir *tdi, const char *name) > clp->name = clp->relpath + strlen(tdi->name) + 1; > clp->krb5_fd = -1; > clp->gssd_fd = -1; > + clp->refcount = 1; > > TAILQ_INSERT_HEAD(&tdi->clnt_list, clp, list); > return clp; > @@ -651,7 +686,7 @@ gssd_scan_topdir(const char *name) > if (clp->scanned) > continue; > > - printerr(3, "destroying client %s\n", clp->relpath); > + printerr(3, "orphaned client %s\n", clp->relpath); > saveprev = clp->list.tqe_prev; > TAILQ_REMOVE(&tdi->clnt_list, clp, list); > gssd_destroy_client(clp); > diff --git a/utils/gssd/gssd.h b/utils/gssd/gssd.h > index f4f59754..d33e4dff 100644 > --- a/utils/gssd/gssd.h > +++ b/utils/gssd/gssd.h > @@ -63,12 +63,10 @@ extern unsigned int context_timeout; > extern unsigned int rpc_timeout; > extern char *preferred_realm; > extern pthread_mutex_t ple_lock; > -extern pthread_cond_t pcond; > -extern pthread_mutex_t pmutex; > -extern int thread_started; > > struct clnt_info { > TAILQ_ENTRY(clnt_info) list; > + int refcount; > int wd; > bool scanned; > char *name; > @@ -94,6 +92,7 @@ struct clnt_upcall_info { > > void handle_krb5_upcall(struct clnt_upcall_info *clp); > void handle_gssd_upcall(struct clnt_upcall_info *clp); > +void free_upcall_info(struct clnt_upcall_info *info); > > > #endif /* _RPC_GSSD_H_ */ > diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c > index 8fe6605b..05c1da64 100644 > --- a/utils/gssd/gssd_proc.c > +++ b/utils/gssd/gssd_proc.c > @@ -730,7 +730,7 @@ handle_krb5_upcall(struct clnt_upcall_info *info) > printerr(2, "\n%s: uid %d (%s)\n", __func__, info->uid, clp->relpath); > > process_krb5_upcall(clp, info->uid, clp->krb5_fd, NULL, NULL, NULL); > - free(info); > + free_upcall_info(info); > } > > void > @@ -830,6 +830,6 @@ handle_gssd_upcall(struct clnt_upcall_info *info) > out: > free(upcall_str); > out_nomem: > - free(info); > + free_upcall_info(info); > return; > } > -- > 2.26.2 >