[Devel] [PATCH RHEL7 COMMIT] fs/fuse: fix unsafe killing fiq->pending requests

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-957.1.3.vz7.83.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.1.3.vz7.83.10
------>
commit b2ed0ef640af1073f0048e5171aa9e0fd86f1f55
Author: Pavel Butsykin <pbutsykin at virtuozzo.com>
Date:   Mon Feb 4 12:27:55 2019 +0300

    fs/fuse: fix unsafe killing fiq->pending requests
    
    There are two problems related to the lack of fiq locking in
    fuse_invalidate_files(). The first is an unsafe iteration of
    fiq->pending list in fuse_kill_requests(). The second problem
    is the race between __fuse_request_send() and fuse_invalidate_files():
    
    __fuse_request_send():                                  fuse_invalidate_files():
    spin_lock(&fiq->waitq.lock);
    test_bit(FUSE_S_FAIL_IMMEDIATELY, &ff->ff_state)
                                                            spin_lock(&fc->lock);
                                                            list_for_each_entry(ff, &fi->rw_files, rw_entry)
                                                              set_bit(FUSE_S_FAIL_IMMEDIATELY, &ff->ff_state);
                                                            spin_unlock(&fc->lock);
    
                                                            spin_lock(&fc->lock);
    
                                                            spin_lock(&fpq->lock);
                                                            fuse_kill_requests(fc, inode, &fiq->pending);
                                                            spin_unlock(&fpq->lock);
                                                            spin_unlock(&fc->lock);
    
    queue_request(fiq, req);    <-- add a new request after fuse_invalidate_files(),
    spin_unlock(&fiq->waitq.lock);  that's wrong.
    
    The patch fixes both problems.
    
    Signed-off-by: Pavel Butsykin <pbutsykin at virtuozzo.com>
    Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 fs/fuse/inode.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index cb275ff21991..80bfe45d5d46 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -437,9 +437,12 @@ int fuse_invalidate_files(struct fuse_conn *fc, u64 nodeid)
 			spin_lock(&fpq->lock);
 			for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
 				fuse_kill_requests(fc, inode, &fpq->processing[i]);
-			fuse_kill_requests(fc, inode, &fiq->pending);
 			fuse_kill_requests(fc, inode, &fpq->io);
 			spin_unlock(&fpq->lock);
+
+			spin_lock(&fiq->waitq.lock);
+			fuse_kill_requests(fc, inode, &fiq->pending);
+			spin_unlock(&fiq->waitq.lock);
 		}
 		fuse_kill_requests(fc, inode, &fc->main_iq.pending);
 		fuse_kill_requests(fc, inode, &fc->bg_queue);