afs_dynroot_readdir() uses the RCU read lock to walk the cell list whilst
emitting cell automount entries - but dir_emit() may write to a userspace
buffer, thereby causing a fault to occur and waits to happen.
Fix afs_dynroot_readdir() to get a shared lock on net->cells_lock instead.
This can be triggered by enabling lockdep, preconfiguring a number of
cells, doing "mount -t afs none /afs -o dyn" (or using the kafs-client
package with afs.mount systemd unit enabled) and then doing "ls /afs".
Fixes: 1d0b929fc070 ("afs: Change dynroot to create contents on demand")
Reported-by: syzbot+3b6c5c6a1d0119b687a1@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+8245611446194a52150d@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+1aa62e6852a6ad1c7944@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+54e6c2176ba76c56217e@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
fs/afs/dynroot.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c
index 691e0ae607a1..8c6130789fde 100644
--- a/fs/afs/dynroot.c
+++ b/fs/afs/dynroot.c
@@ -348,9 +348,9 @@ static int afs_dynroot_readdir(struct file *file, struct dir_context *ctx)
}
if ((unsigned long long)ctx->pos <= AFS_MAX_DYNROOT_CELL_INO) {
- rcu_read_lock();
+ down_read(&net->cells_lock);
ret = afs_dynroot_readdir_cells(net, ctx);
- rcu_read_unlock();
+ up_read(&net->cells_lock);
}
return ret;
}
