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().
Doug
From 8ef49081e8a42bfa05bb63265cd4f951e2b23413 Mon Sep 17 00:00:00 2001
From: Doug Nazar <nazard@xxxxxxxx>
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 <sebastian.kraus@xxxxxxxxxxxx>
Signed-off-by: Doug Nazar <nazard@xxxxxxxx>
---
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
