Re: [nfs-utils RFC PATCH 1/2] gssd: deal with failed thread creation

[Scott Mayhew <smayhew@redhat.com>]

On Tue, 25 May 2021, Steve Dickson wrote:

> Hey!
> 
> Just a couple of nits... 
> 
> On 5/25/21 2:00 PM, Scott Mayhew wrote:
> > If we fail to create a thread to handle an upcall, we still need to do a
> > downcall to tell the kernel about the failure, otherwise the process
> > that is trying to establish gss credentials will hang.
> > 
> > This patch shifts the thread creation down a level in the call chain so
> > now the main thread does a little more work up front (reading & parsing
> > the data from the pipefs file) so it has the info it needs to be able
> > to do the error downcall.
> > 
> > Signed-off-by: Scott Mayhew <smayhew@redhat.com>
> > ---
> >  utils/gssd/gssd.c      |  83 +-----------------
> >  utils/gssd/gssd.h      |  11 ++-
> >  utils/gssd/gssd_proc.c | 190 +++++++++++++++++++++++++++++++++--------
> >  3 files changed, 166 insertions(+), 118 deletions(-)
> > 
> > diff --git a/utils/gssd/gssd.c b/utils/gssd/gssd.c
> > index 1541d371..eb440470 100644
> > --- a/utils/gssd/gssd.c
> > +++ b/utils/gssd/gssd.c
> > @@ -364,7 +364,7 @@ out:
> >  /* Actually frees clp and fields that might be used from other
> >   * threads if was last reference.
> >   */
> > -static void
> > +void
> >  gssd_free_client(struct clnt_info *clp)
> >  {
> >  	int refcnt;
> > @@ -416,55 +416,6 @@ gssd_destroy_client(struct clnt_info *clp)
> >  
> >  static void gssd_scan(void);
> >  
> > -static int
> > -start_upcall_thread(void (*func)(struct clnt_upcall_info *), void *info)
> > -{
> > -	pthread_attr_t attr;
> > -	pthread_t th;
> > -	int ret;
> > -
> > -	ret = pthread_attr_init(&attr);
> > -	if (ret != 0) {
> > -		printerr(0, "ERROR: failed to init pthread attr: ret %d: %s\n",
> > -			 ret, strerror(errno));
> > -		return ret;
> > -	}
> > -	ret = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
> > -	if (ret != 0) {
> > -		printerr(0, "ERROR: failed to create pthread attr: ret %d: "
> > -			 "%s\n", ret, strerror(errno));
> > -		return ret;
> > -	}
> > -
> > -	ret = pthread_create(&th, &attr, (void *)func, (void *)info);
> > -	if (ret != 0)
> > -		printerr(0, "ERROR: pthread_create failed: ret %d: %s\n",
> > -			 ret, strerror(errno));
> > -	return ret;
> > -}
> > -
> > -static struct clnt_upcall_info *alloc_upcall_info(struct clnt_info *clp)
> > -{
> > -	struct clnt_upcall_info *info;
> > -
> > -	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.
> > @@ -473,44 +424,16 @@ static void
> >  gssd_clnt_gssd_cb(int UNUSED(fd), short UNUSED(which), void *data)
> >  {
> >  	struct clnt_info *clp = data;
> > -	struct clnt_upcall_info *info;
> > -
> > -	info = alloc_upcall_info(clp);
> > -	if (info == NULL)
> > -		return;
> >  
> > -	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_upcall_info(info);
> > -		return;
> > -	}
> > -	info->lbuf[info->lbuflen-1] = 0;
> > -
> > -	if (start_upcall_thread(handle_gssd_upcall, info))
> > -		free_upcall_info(info);
> > +	handle_gssd_upcall(clp);
> >  }
> >  
> >  static void
> >  gssd_clnt_krb5_cb(int UNUSED(fd), short UNUSED(which), void *data)
> >  {
> >  	struct clnt_info *clp = data;
> > -	struct clnt_upcall_info *info;
> > -
> > -	info = alloc_upcall_info(clp);
> > -	if (info == NULL)
> > -		return;
> > -
> > -	if (read(clp->krb5_fd, &info->uid,
> > -			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_upcall_info(info);
> > -		return;
> > -	}
> >  
> > -	if (start_upcall_thread(handle_krb5_upcall, info))
> > -		free_upcall_info(info);
> > +	handle_krb5_upcall(clp);
> >  }
> >  
> >  static struct clnt_info *
> > diff --git a/utils/gssd/gssd.h b/utils/gssd/gssd.h
> > index 1e8c58d4..6d53647e 100644
> > --- a/utils/gssd/gssd.h
> > +++ b/utils/gssd/gssd.h
> > @@ -84,14 +84,17 @@ struct clnt_info {
> >  
> >  struct clnt_upcall_info {
> >  	struct clnt_info 	*clp;
> > -	char			lbuf[RPC_CHAN_BUF_SIZE];
> > -	int			lbuflen;
> >  	uid_t			uid;
> > +	int			fd;
> > +	char			*srchost;
> > +	char			*target;
> > +	char			*service;
> >  };
> >  
> > -void handle_krb5_upcall(struct clnt_upcall_info *clp);
> > -void handle_gssd_upcall(struct clnt_upcall_info *clp);
> > +void handle_krb5_upcall(struct clnt_info *clp);
> > +void handle_gssd_upcall(struct clnt_info *clp);
> >  void free_upcall_info(struct clnt_upcall_info *info);
> > +void gssd_free_client(struct clnt_info *clp);
> >  
> >  
> >  #endif /* _RPC_GSSD_H_ */
> > diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c
> > index e830f497..ba508b30 100644
> > --- a/utils/gssd/gssd_proc.c
> > +++ b/utils/gssd/gssd_proc.c
> > @@ -80,6 +80,8 @@
> >  #include "nfslib.h"
> >  #include "gss_names.h"
> >  
> > +extern pthread_mutex_t clp_lock;
> > +
> >  /* Encryption types supported by the kernel rpcsec_gss code */
> >  int num_krb5_enctypes = 0;
> >  krb5_enctype *krb5_enctypes = NULL;
> > @@ -723,22 +725,135 @@ out_return_error:
> >  	goto out;
> >  }
> >  
> > -void
> > -handle_krb5_upcall(struct clnt_upcall_info *info)
> > +static struct clnt_upcall_info *
> > +alloc_upcall_info(struct clnt_info *clp, uid_t uid, int fd, char *srchost,
> > +		  char *target, char *service)
> >  {
> > -	struct clnt_info *clp = info->clp;
> > +	struct clnt_upcall_info *info;
> > +
> > +	info = malloc(sizeof(struct clnt_upcall_info));
> > +	if (info == NULL)
> > +		return NULL;
> > +
> > +	memset(info, 0, sizeof(*info));
> > +	pthread_mutex_lock(&clp_lock);
> > +	clp->refcount++;
> > +	pthread_mutex_unlock(&clp_lock);
> > +	info->clp = clp;
> > +	info->uid = uid;
> > +	info->fd = fd;
> > +	if (srchost) {
> > +		info->srchost = strdup(srchost);
> > +		if (info->srchost == NULL)
> > +			goto out_info;
> > +	}
> > +	if (target) {
> > +		info->target = strdup(target);
> > +		if (info->target == NULL)
> > +			goto out_srchost;
> > +	}
> > +	if (service) {
> > +		info->service = strdup(service);
> > +		if (info->service == NULL)
> > +			goto out_target;
> > +	}
> > +
> > +out:
> > +	return info;
> > +
> > +out_target:
> > +	if (info->target)
> > +		free(info->target);
> > +out_srchost:
> > +	if (info->srchost)
> > +		free(info->srchost);
> > +out_info:
> > +	free(info);
> > +	info = NULL;
> > +	goto out;
> > +}
> >  
> > -	printerr(2, "\n%s: uid %d (%s)\n", __func__, info->uid, clp->relpath);
> > +void free_upcall_info(struct clnt_upcall_info *info)
> > +{
> > +	gssd_free_client(info->clp);
> > +	if (info->service)
> > +		free(info->service);
> > +	if (info->target)
> > +		free(info->target);
> > +	if (info->srchost)
> > +		free(info->srchost);
> > +	free(info);
> > +}
> >  
> > -	process_krb5_upcall(clp, info->uid, clp->krb5_fd, NULL, NULL, NULL);
> > +static void
> > +gssd_work_thread_fn(struct clnt_upcall_info *info)
> > +{
> > +	process_krb5_upcall(info->clp, info->uid, info->fd, info->srchost, info->target, info->service);
> >  	free_upcall_info(info);
> >  }
> >  
> > +static int
> > +start_upcall_thread(void (*func)(struct clnt_upcall_info *), void *info)
> > +{
> > +	pthread_attr_t attr;
> > +	pthread_t th;
> > +	int ret;
> > +
> > +	ret = pthread_attr_init(&attr);
> > +	if (ret != 0) {
> > +		printerr(0, "ERROR: failed to init pthread attr: ret %d: %s\n",
> > +			 ret, strerror(errno));
> > +		return ret;
> > +	}
> > +	ret = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
> > +	if (ret != 0) {
> > +		printerr(0, "ERROR: failed to create pthread attr: ret %d: "
> > +			 "%s\n", ret, strerror(errno));
> > +		return ret;
> > +	}
> > +
> > +	ret = pthread_create(&th, &attr, (void *)func, (void *)info);
> > +	if (ret != 0)
> > +		printerr(0, "ERROR: pthread_create failed: ret %d: %s\n",
> > +			 ret, strerror(errno));
> > +	else
> > +		printerr(0, "created thread id 0x%lx\n", th);
> printerr(0) are used for errors not debugging... But I'm wondering
> if this debug statement is even needed... Since we tids are not
> included in other debugging statements, how would they info be useful?

In the 2nd patch I actually changed it to printerr(1), but yeah we can get
rid of it.  I had a ton of these sprinkled all over the place and for
some reason decided to keep this one.

> 
> 
> > +	return ret;
> > +}
> > +
> > +void
> > +handle_krb5_upcall(struct clnt_info *clp)
> > +{
> > +	uid_t			uid;
> > +	struct clnt_upcall_info	*info;
> > +	int			err;
> > +
> > +	if (read(clp->krb5_fd, &uid, sizeof(uid)) < (ssize_t)sizeof(uid)) {
> > +		printerr(0, "WARNING: failed reading uid from krb5 "
> > +			    "upcall pipe: %s\n", strerror(errno));
> > +		return;
> > +	}
> > +	printerr(2, "\n%s: uid %d (%s)\n", __func__, uid, clp->relpath);
> > +
> > +	info = alloc_upcall_info(clp, uid, clp->krb5_fd, NULL, NULL, NULL);
> > +	if (info == NULL) {
> > +		printerr(0, "%s: failed to allocate clnt_upcall_info\n", __func__);
> > +		do_error_downcall(clp->krb5_fd, uid, -EACCES);
> > +		return;
> > +	}
> > +	err = start_upcall_thread(gssd_work_thread_fn, info);
> > +	if (err != 0) {
> > +		do_error_downcall(clp->krb5_fd, uid, -EACCES);
> > +		free_upcall_info(info);
> > +	}
> > +}
> Why is -EACCES being used in both failures? Shouldn't errno be used
> or at least ENOMEM for the alloc_upcall_info() failure?

I believe the code that handles the downcall in the kernel only looks
for -EACCES and -EKEYEXPIRED.  Anything else gets translated to -EACCES,
so that's why I went ahead and used -EACCES (see gss_fill_context()).

Note that means the kernel will also translate -ETIMEDOUT (from the 2nd
patch) to -EACCES as well... but I don't think it's necessary to change
that behavior really.

-Scott
> 
> Again... these are just nits.. so a repost is not necessary
> Just wanted to get your thoughts on them.
> 
> steved. 
> 
> > +
> >  void
> > -handle_gssd_upcall(struct clnt_upcall_info *info)
> > +handle_gssd_upcall(struct clnt_info *clp)
> >  {
> > -	struct clnt_info	*clp = info->clp;
> >  	uid_t			uid;
> > +	char			lbuf[RPC_CHAN_BUF_SIZE];
> > +	int			lbuflen = 0;
> >  	char			*p;
> >  	char			*mech = NULL;
> >  	char			*uidstr = NULL;
> > @@ -746,20 +861,22 @@ handle_gssd_upcall(struct clnt_upcall_info *info)
> >  	char			*service = NULL;
> >  	char			*srchost = NULL;
> >  	char			*enctypes = NULL;
> > -	char			*upcall_str;
> > -	char			*pbuf = info->lbuf;
> >  	pthread_t tid = pthread_self();
> > +	struct clnt_upcall_info	*info;
> > +	int			err;
> >  
> > -	printerr(2, "\n%s(0x%x): '%s' (%s)\n", __func__, tid, 
> > -		info->lbuf, clp->relpath);
> > -
> > -	upcall_str = strdup(info->lbuf);
> > -	if (upcall_str == NULL) {
> > -		printerr(0, "ERROR: malloc failure\n");
> > -		goto out_nomem;
> > +	lbuflen = read(clp->gssd_fd, lbuf, sizeof(lbuf));
> > +	if (lbuflen <= 0 || lbuf[lbuflen-1] != '\n') {
> > +		printerr(0, "WARNING: handle_gssd_upcall: "
> > +			    "failed reading request\n");
> > +		return;
> >  	}
> > +	lbuf[lbuflen-1] = 0;
> > +
> > +	printerr(2, "\n%s(0x%x): '%s' (%s)\n", __func__, tid,
> > +		 lbuf, clp->relpath);
> >  
> > -	while ((p = strsep(&pbuf, " "))) {
> > +	for (p = strtok(lbuf, " "); p; p = strtok(NULL, " ")) {
> >  		if (!strncmp(p, "mech=", strlen("mech=")))
> >  			mech = p + strlen("mech=");
> >  		else if (!strncmp(p, "uid=", strlen("uid=")))
> > @@ -777,8 +894,8 @@ handle_gssd_upcall(struct clnt_upcall_info *info)
> >  	if (!mech || strlen(mech) < 1) {
> >  		printerr(0, "WARNING: handle_gssd_upcall: "
> >  			    "failed to find gss mechanism name "
> > -			    "in upcall string '%s'\n", upcall_str);
> > -		goto out;
> > +			    "in upcall string '%s'\n", lbuf);
> > +		return;
> >  	}
> >  
> >  	if (uidstr) {
> > @@ -790,21 +907,21 @@ handle_gssd_upcall(struct clnt_upcall_info *info)
> >  	if (!uidstr) {
> >  		printerr(0, "WARNING: handle_gssd_upcall: "
> >  			    "failed to find uid "
> > -			    "in upcall string '%s'\n", upcall_str);
> > -		goto out;
> > +			    "in upcall string '%s'\n", lbuf);
> > +		return;
> >  	}
> >  
> >  	if (enctypes && parse_enctypes(enctypes) != 0) {
> >  		printerr(0, "WARNING: handle_gssd_upcall: "
> >  			 "parsing encryption types failed: errno %d\n", errno);
> > -		goto out;
> > +		return;
> >  	}
> >  
> >  	if (target && strlen(target) < 1) {
> >  		printerr(0, "WARNING: handle_gssd_upcall: "
> >  			 "failed to parse target name "
> > -			 "in upcall string '%s'\n", upcall_str);
> > -		goto out;
> > +			 "in upcall string '%s'\n", lbuf);
> > +		return;
> >  	}
> >  
> >  	/*
> > @@ -818,21 +935,26 @@ handle_gssd_upcall(struct clnt_upcall_info *info)
> >  	if (service && strlen(service) < 1) {
> >  		printerr(0, "WARNING: handle_gssd_upcall: "
> >  			 "failed to parse service type "
> > -			 "in upcall string '%s'\n", upcall_str);
> > -		goto out;
> > +			 "in upcall string '%s'\n", lbuf);
> > +		return;
> >  	}
> >  
> > -	if (strcmp(mech, "krb5") == 0 && clp->servername)
> > -		process_krb5_upcall(clp, uid, clp->gssd_fd, srchost, target, service);
> > -	else {
> > +	if (strcmp(mech, "krb5") == 0 && clp->servername) {
> > +		info = alloc_upcall_info(clp, uid, clp->gssd_fd, srchost, target, service);
> > +		if (info == NULL) {
> > +			printerr(0, "%s: failed to allocate clnt_upcall_info\n", __func__);
> > +			do_error_downcall(clp->gssd_fd, uid, -EACCES);
> > +			return;
> > +		}
> > +		err = start_upcall_thread(gssd_work_thread_fn, info);
> > +		if (err != 0) {
> > +			do_error_downcall(clp->gssd_fd, uid, -EACCES);
> > +			free_upcall_info(info);
> > +		}
> > +	} else {
> >  		if (clp->servername)
> >  			printerr(0, "WARNING: handle_gssd_upcall: "
> >  				 "received unknown gss mech '%s'\n", mech);
> >  		do_error_downcall(clp->gssd_fd, uid, -EACCES);
> >  	}
> > -out:
> > -	free(upcall_str);
> > -out_nomem:
> > -	free_upcall_info(info);
> > -	return;
> >  }
> > 
>