NFSD: Fix potential use-after-free in nfsd_file_put()

nfsd_file_put_noref() can free @nf, so don't dereference @nf
immediately upon return from nfsd_file_put_noref().

Suggested-by: Trond Myklebust <trondmy@hammerspace.com>
Fixes: 999397926ab3 ("nfsd: Clean up nfsd_file_put()")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index d32fcd8..148b25a 100644 (file)
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -308,11 +308,12 @@ nfsd_file_put(struct nfsd_file *nf)
        if (test_bit(NFSD_FILE_HASHED, &nf->nf_flags) == 0) {
                nfsd_file_flush(nf);
                nfsd_file_put_noref(nf);
-       } else {
+       } else if (nf->nf_file) {
                nfsd_file_put_noref(nf);
-               if (nf->nf_file)
-                       nfsd_file_schedule_laundrette();
-       }
+               nfsd_file_schedule_laundrette();
+       } else
+               nfsd_file_put_noref(nf);
+
        if (atomic_long_read(&nfsd_filecache_count) >= NFSD_FILE_LRU_LIMIT)
                nfsd_file_gc();
 }