[PATCH] afs: Fix afs_atcell_get_link() to check if ws_cell is unset first

[PATCH] afs: Fix afs_atcell_get_link() to check if ws_cell is unset first

[David Howells]

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@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: syzbot+76a6f18e3af82e84f264@syzkaller.appspotmail.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-fsdevel@vger.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));

Re: [PATCH] afs: Fix afs_atcell_get_link() to check if ws_cell is unset first

[Edward Adam Davis]

On Tue, 18 Mar 2025 11:20:19 +0000, David Howells wrote:
> 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@syzkaller.appspotmail.com
> Signed-off-by: David Howells <dhowells@redhat.com>
> Tested-by: syzbot+76a6f18e3af82e84f264@syzkaller.appspotmail.com
> cc: Marc Dionne <marc.dionne@auristor.com>
> cc: linux-afs@lists.infradead.org
> cc: linux-fsdevel@vger.kernel.org
My fix already sent, it is much earlier than your patch.
https://lore.kernel.org/all/tencent_8CA5671E3C533638973237484A0874917609@qq.com/

BR,
Edward

Re: [PATCH] afs: Fix afs_atcell_get_link() to check if ws_cell is unset first

[Christian Brauner]

On Tue, 18 Mar 2025 11:20:19 +0000, David Howells wrote:
> Fix afs_atcell_get_link() to check if the workstation cell is unset before
> doing the RCU pathwalk bit where we dereference that.
> 
> 

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] afs: Fix afs_atcell_get_link() to check if ws_cell is unset first
      https://git.kernel.org/vfs/vfs/c/0307d16f3610