[PATCH v4 06/19] liveupdate: Don't WARN if tracking a retrieved file fails

[David Matlack <dmatlack@google.com>]

Handle a failure to add a retrieved file to luo_preserved_files instead
of triggering a WARN_ON(). Make the failure permanent, and keep the file
until the file set is finished, like any other retrieved file. Only warn
if the file is already tracked (-EBUSY), which would be a kernel bug,
since a retrieved file is always a new file.

xa_insert() can fail with -ENOMEM, and userspace can trigger that with
LIVEUPDATE_SESSION_RETRIEVE_FD, so warning about it lets userspace crash
systems with panic_on_warn.

The handler has already consumed the preserved state when this happens,
so the retrieve can't be retried. Keeping the file ensures that its
resources are not released before the file set is finished. Finishing
the file set then erases the file from luo_preserved_files, which does
nothing for a file that was never added.

Fixes: 00d0b372374f ("liveupdate: prevent double management of files")
Signed-off-by: David Matlack <dmatlack@google.com>
Acked-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 kernel/liveupdate/luo_file.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 0c9a3b6921d1..e5d333649f76 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -668,14 +668,28 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token,
 		return err;
 	}
 
+	err = xa_insert(&luo_preserved_files,
+			luo_get_id(luo_file->fh, args.file), args.file,
+			GFP_KERNEL);
+	if (err) {
+		/* A retrieved file is new, so it can't be tracked already. */
+		WARN_ON_ONCE(err == -EBUSY);
+
+		/*
+		 * The handler has consumed the preserved state, so the retrieve
+		 * can't be retried. Keep the file until the file set is
+		 * finished, so that its resources are released at the same
+		 * time as those of other retrieved files.
+		 */
+		luo_file->file = args.file;
+		luo_file->retrieve_status = err;
+		return err;
+	}
+
 	luo_file->file = args.file;
 	/* Get reference so we can keep this file in LUO until finish */
 	get_file(luo_file->file);
 
-	WARN_ON(xa_insert(&luo_preserved_files,
-			  luo_get_id(luo_file->fh, luo_file->file),
-			  luo_file->file, GFP_KERNEL));
-
 	*filep = luo_file->file;
 	luo_file->retrieve_status = 1;
 
-- 
2.56.0.542.g3ef89b7020-goog