fuse: avoid out-of-scope stack access

The all pointers within fuse_req must point to valid memory once
fuse_force_forget() returns.

This bug appeared in "fuse: implement NFS-like readdirplus support"
and was never in any official Linux release.

I tested the fuse_force_forget() code path by injecting to fake -ENOMEM and
verified the FORGET operation was called properly in userspace.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index cbae09e5a491..e9bdec0b16d9 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -440,9 +440,8 @@ __acquires(fc->lock)
         }
 }
 
-void fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
+static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
 {
-        req->isreply = 1;
         spin_lock(&fc->lock);
         if (!fc->connected)
                 req->out.h.error = -ENOTCONN;
@@ -459,6 +458,12 @@ void fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
         }
         spin_unlock(&fc->lock);
 }
+
+void fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
+{
+        req->isreply = 1;
+        __fuse_request_send(fc, req);
+}
 EXPORT_SYMBOL_GPL(fuse_request_send);
 
 static void fuse_request_send_nowait_locked(struct fuse_conn *fc,
@@ -541,7 +546,9 @@ void fuse_force_forget(struct file *file, u64 nodeid)
         req->in.args[0].size = sizeof(inarg);
         req->in.args[0].value = &inarg;
         req->isreply = 0;
-        fuse_request_send_nowait(fc, req);
+        __fuse_request_send(fc, req);
+        /* ignore errors */
+        fuse_put_request(fc, req);
 }
 
 /*