IB/uverbs: Fix ordering of ucontext check in ib_uverbs_write

During disassociation the ucontext will become NULL, however due to how
the SRCU locking works the ucontext must only be examined after looking
at the ib_dev, which governs the RCU control flow.

With the wrong ordering userspace will see EINVAL instead of EIO for a
disassociated uverbs FD, which breaks rdma-core.

Cc: stable@vger.kernel.org
Fixes: 491d5c6a3023 ("RDMA/uverbs: Move uncontext check before SRCU read lock")
Reported-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>

diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 3ae2339..2094d13 100644 (file)
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -736,10 +736,6 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
        if (ret)
                return ret;
 
-       if (!file->ucontext &&
-           (command != IB_USER_VERBS_CMD_GET_CONTEXT || extended))
-               return -EINVAL;
-
        if (extended) {
                if (count < (sizeof(hdr) + sizeof(ex_hdr)))
                        return -EINVAL;
@@ -759,6 +755,16 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
                goto out;
        }
 
+       /*
+        * Must be after the ib_dev check, as once the RCU clears ib_dev ==
+        * NULL means ucontext == NULL
+        */
+       if (!file->ucontext &&
+           (command != IB_USER_VERBS_CMD_GET_CONTEXT || extended)) {
+               ret = -EINVAL;
+               goto out;
+       }
+
        if (!verify_command_mask(ib_dev, command, extended)) {
                ret = -EOPNOTSUPP;
                goto out;