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>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 3ae2339dd27a..2094d136513d 100644
--- 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;