[PATCH] pNFS: Fix use-after-free in pnfs_update_layout()

[Wentao Liang]

When hitting the NFS_LAYOUT_RETURN branch in pnfs_update_layout(),
the code calls pnfs_prepare_to_retry_layoutget(lo). If it succeeds,
pnfs_put_layout_hdr(lo) is called before trace_pnfs_update_layout(),
which still references 'lo'. This results in a use-after-free when the
tracepoint accesses lo's fields.

Fix this by moving the tracepoint call before pnfs_put_layout_hdr(lo).

Fixes: 2c8d5fc37fe2 ("pNFS: Stricter ordering of layoutget and layoutreturn")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Wentao Liang <vulab@xxxxxxxxxxx>
---
 fs/nfs/pnfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index a3135b5af7ee..42e5f8ec31d4 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -2191,11 +2191,11 @@ pnfs_update_layout(struct inode *ino,
 		dprintk("%s wait for layoutreturn\n", __func__);
 		lseg = ERR_PTR(pnfs_prepare_to_retry_layoutget(lo));
 		if (!IS_ERR(lseg)) {
-			pnfs_put_layout_hdr(lo);
 			dprintk("%s retrying\n", __func__);
 			trace_pnfs_update_layout(ino, pos, count, iomode, lo,
 						 lseg,
 						 PNFS_UPDATE_LAYOUT_RETRY);
+			pnfs_put_layout_hdr(lo);
 			goto lookup_again;
 		}
 		trace_pnfs_update_layout(ino, pos, count, iomode, lo, lseg,
-- 
2.34.1