linux-kernel - [PATCH] eventfs: Don't return NULL in eventfs_create

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Message-ID: <20240723122522.2724-1-minipli@grsecurity.net>
Date: Tue, 23 Jul 2024 14:25:21 +0200
From: Mathias Krause <minipli@...ecurity.net>
To: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathias Krause <minipli@...ecurity.net>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-trace-kernel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Ajay Kaher <ajay.kaher@...adcom.com>
Subject: [PATCH] eventfs: Don't return NULL in eventfs_create_dir()

Commit 77a06c33a22d ("eventfs: Test for ei->is_freed when accessing
ei->dentry") added another check, testing if the parent was freed after
we released the mutex. If so, the function returns NULL. However, all
callers expect it to either return a valid pointer or an error pointer,
at least since commit 5264a2f4bb3b ("tracing: Fix a NULL vs IS_ERR() bug
in event_subsystem_dir()"). Returning NULL will therefore fail the error
condition check in the caller.

Fix this by substituting the NULL return value with a fitting error
pointer.

Fixes: 77a06c33a22d ("eventfs: Test for ei->is_freed when accessing ei->dentry")
Reviewed-by: Dan Carpenter <dan.carpenter@...aro.org>
Reviewed-by: Ajay Kaher <ajay.kaher@...adcom.com>
Signed-off-by: Mathias Krause <minipli@...ecurity.net>
---
v2: send as a separate patch, picking up review tags from Dan and Ajay

 fs/tracefs/event_inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 5d88c184f0fc..a9c28a1d5dc8 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -736,7 +736,7 @@ struct eventfs_inode *eventfs_create_dir(const char *name, struct eventfs_inode
 	/* Was the parent freed? */
 	if (list_empty(&ei->list)) {
 		cleanup_ei(ei);
-		ei = NULL;
+		ei = ERR_PTR(-EBUSY);
 	}
 	return ei;
 }
-- 
2.43.0