[PATCH] orangefs: fix double-free of trailer_buf on readdir copy failure

[Yifei Gao <gyf161023@gmail.com>]

On a readdir downcall, orangefs_devreq_write_iter() frees
op->downcall.trailer_buf with vfree() when copy_from_iter_full() fails,
but does not clear the pointer before goto Efault. The waiter in
do_readdir() is then woken with a negative status and frees the same
pointer again on its r < 0 path, causing a deterministic double-free.
A client holding /dev/pvfs2-req triggers it by sending a readdir
downcall whose declared trailer_size exceeds the bytes it supplies.

Clear the pointer after freeing so the readdir-side vfree() becomes a
no-op.

Fixes: 382f4581e67f ("orangefs: rewrite readdir to fix several bugs")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Yifei Gao <gyf161023@gmail.com>
---
 fs/orangefs/devorangefs-req.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/orangefs/devorangefs-req.c b/fs/orangefs/devorangefs-req.c
index 33ee8cb32f83..e5c60da7e677 100644
--- a/fs/orangefs/devorangefs-req.c
+++ b/fs/orangefs/devorangefs-req.c
@@ -474,6 +474,7 @@ static ssize_t orangefs_devreq_write_iter(struct kiocb *iocb,
 			         op->downcall.trailer_size, iter)) {
 		gossip_err("%s: failed to copy trailer.\n", __func__);
 		vfree(op->downcall.trailer_buf);
+		op->downcall.trailer_buf = NULL;
 		goto Efault;
 	}
 
-- 
2.43.0