From 75893c058b21d87d1ec66bbd4e8bf84e1fd616d1 Mon Sep 17 00:00:00 2001 From: Christian Schoenebeck Date: Tue, 16 Jun 2026 17:00:11 +0200 Subject: [PATCH] hw/9pfs/local: harden local_fid_fd() on FID types local_fid_fd() returns fs->fd for any FID type that is not P9_FID_DIR. Since P9_FID_XATTR and P9_FID_NONE share union V9fsFidOpenState, calling local_fid_fd() on these types misinterprets xattr state as a file descriptor, potentially leading to undefined behaviour or information disclosure. Even though we are catching these FID type mismatches on protocol level in 9p.c already, previous patches proofed this to be error prone. So let's add another safety layer in local_fid_fd() that would return -1 if the FID type would not possess a valid file descriptor, to prevent wrong file descriptors from reaching fs backend calls. Link: https://lore.kernel.org/qemu-devel/531f6b81bc1bf1a48c3d4afaa60a65db10511041.1781621428.git.qemu_oss@crudebyte.com Signed-off-by: Christian Schoenebeck --- hw/9pfs/9p-local.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c index 4708e170a4..ee592b62f8 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -775,8 +775,11 @@ static int local_fid_fd(int fid_type, V9fsFidOpenState *fs) { if (fid_type == P9_FID_DIR) { return dirfd(fs->dir.stream); - } else { + } else if (fid_type == P9_FID_FILE) { return fs->fd; + } else { + errno = EBADF; + return -1; } }