From: Stefan Hajnoczi <stefanha@redhat.com>

Date: Mon, 27 Jan 2020 19:02:20 +0000

Subject: [PATCH] virtiofsd: prevent FUSE_INIT/FUSE_DESTROY races

When running with multiple threads it can be tricky to handle

FUSE_INIT/FUSE_DESTROY in parallel with other request types or in

parallel with themselves.  Serialize FUSE_INIT and FUSE_DESTROY so that

malicious clients cannot trigger race conditions.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

(cherry picked from commit cdc497c6925be745bc895355bd4674a17a4b2a8b)

---

 tools/virtiofsd/fuse_i.h        |  1 +

 tools/virtiofsd/fuse_lowlevel.c | 18 ++++++++++++++++++

 2 files changed, 19 insertions(+)

diff --git a/tools/virtiofsd/fuse_i.h b/tools/virtiofsd/fuse_i.h

index a20854f1c4..1447d86866 100644

--- a/tools/virtiofsd/fuse_i.h

+++ b/tools/virtiofsd/fuse_i.h

@@ -61,6 +61,7 @@ struct fuse_session {

     struct fuse_req list;

     struct fuse_req interrupts;

     pthread_mutex_t lock;

+    pthread_rwlock_t init_rwlock;

     int got_destroy;

     int broken_splice_nonblock;

     uint64_t notify_ctr;

diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c

index dab6a31e08..79a4031266 100644

--- a/tools/virtiofsd/fuse_lowlevel.c

+++ b/tools/virtiofsd/fuse_lowlevel.c

@@ -2428,6 +2428,19 @@ void fuse_session_process_buf_int(struct fuse_session *se,

     req->ctx.pid = in->pid;

     req->ch = ch;

+    /*

+     * INIT and DESTROY requests are serialized, all other request types

+     * run in parallel.  This prevents races between FUSE_INIT and ordinary

+     * requests, FUSE_INIT and FUSE_INIT, FUSE_INIT and FUSE_DESTROY, and

+     * FUSE_DESTROY and FUSE_DESTROY.

+     */

+    if (in->opcode == FUSE_INIT || in->opcode == CUSE_INIT ||

+        in->opcode == FUSE_DESTROY) {

+        pthread_rwlock_wrlock(&se->init_rwlock);

+    } else {

+        pthread_rwlock_rdlock(&se->init_rwlock);

+    }

+

     err = EIO;

     if (!se->got_init) {

         enum fuse_opcode expected;

@@ -2485,10 +2498,13 @@ void fuse_session_process_buf_int(struct fuse_session *se,

     } else {

         fuse_ll_ops[in->opcode].func(req, in->nodeid, &iter);

     }

+

+    pthread_rwlock_unlock(&se->init_rwlock);

     return;

 reply_err:

     fuse_reply_err(req, err);

+    pthread_rwlock_unlock(&se->init_rwlock);

 }

 #define LL_OPTION(n, o, v)                     \

@@ -2531,6 +2547,7 @@ void fuse_session_destroy(struct fuse_session *se)

             se->op.destroy(se->userdata);

         }

     }

+    pthread_rwlock_destroy(&se->init_rwlock);

     pthread_mutex_destroy(&se->lock);

     free(se->cuse_data);

     if (se->fd != -1) {

@@ -2610,6 +2627,7 @@ struct fuse_session *fuse_session_new(struct fuse_args *args,

     list_init_req(&se->list);

     list_init_req(&se->interrupts);

     fuse_mutex_init(&se->lock);

+    pthread_rwlock_init(&se->init_rwlock, NULL);

     memcpy(&se->op, op, op_size);

     se->owner = getuid();