linux-kernel - [PATCH] afs: Fix afs_atcell_get_link() to check if ws

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Message-ID: <2481796.1742296819@warthog.procyon.org.uk>
Date: Tue, 18 Mar 2025 11:20:19 +0000
From: David Howells <dhowells@...hat.com>
To: Christian Brauner <brauner@...nel.org>
cc: dhowells@...hat.com, Marc Dionne <marc.dionne@...istor.com>,
    syzbot+76a6f18e3af82e84f264@...kaller.appspotmail.com,
    linux-afs@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
    linux-kernel@...r.kernel.org
Subject: [PATCH] afs: Fix afs_atcell_get_link() to check if ws_cell is unset first

Fix afs_atcell_get_link() to check if the workstation cell is unset before
doing the RCU pathwalk bit where we dereference that.

Fixes: 823869e1e616 ("afs: Fix afs_atcell_get_link() to handle RCU pathwalk")
Reported-by: syzbot+76a6f18e3af82e84f264@...kaller.appspotmail.com
Signed-off-by: David Howells <dhowells@...hat.com>
Tested-by: syzbot+76a6f18e3af82e84f264@...kaller.appspotmail.com
cc: Marc Dionne <marc.dionne@...istor.com>
cc: linux-afs@...ts.infradead.org
cc: linux-fsdevel@...r.kernel.org
---
 fs/afs/dynroot.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c
index 9732a1e17db3..691e0ae607a1 100644
--- a/fs/afs/dynroot.c
+++ b/fs/afs/dynroot.c
@@ -210,6 +210,9 @@ static const char *afs_atcell_get_link(struct dentry *dentry, struct inode *inod
 	const char *name;
 	bool dotted = vnode->fid.vnode == 3;
 
+	if (!rcu_access_pointer(net->ws_cell))
+		return ERR_PTR(-ENOENT);
+
 	if (!dentry) {
 		/* We're in RCU-pathwalk. */
 		cell = rcu_dereference(net->ws_cell);
@@ -221,9 +224,6 @@ static const char *afs_atcell_get_link(struct dentry *dentry, struct inode *inod
 		return name;
 	}
 
-	if (!rcu_access_pointer(net->ws_cell))
-		return ERR_PTR(-ENOENT);
-
 	down_read(&net->cells_lock);
 
 	cell = rcu_dereference_protected(net->ws_cell, lockdep_is_held(&net->cells_lock));