@samitouri / QOSamiQemu / commits / 75893c058b

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 <qemu_oss@crudebyte.com>

Christian Schoenebeck committed Jun 16, 2026 at 17:00 UTC 75893c058b21d87d1ec66bbd4e8bf84e1fd616d1

1 file changed +4 -1

hw/9pfs/9p-local.c

+4 -1

@@ -775,8 +775,11 @@ static int local_fid_fd(int fid_type, V9fsFidOpenState *fs)

775 {

776 if (fid_type == P9_FID_DIR) {

777 return dirfd(fs->dir.stream);

778 - } else {

778 + } else if (fid_type == P9_FID_FILE) {

779 return fs->fd;

780 + } else {

781 + errno = EBADF;

782 + return -1;

783 }

784 }

785