From 02e117b8ca58928f193e5b4df48d6763232f5e91 Mon Sep 17 00:00:00 2001 From: "Pratyush Yadav (Google)" Date: Thu, 22 Jan 2026 16:18:40 +0100 Subject: [PATCH] mm: memfd_luo: use memfd_alloc_file() instead of shmem_file_setup() When restoring a memfd, the file is created using shmem_file_setup(). While memfd creation also calls this function to get the file, it also does other things: 1. The O_LARGEFILE flag is set on the file. If this is not done, writes on the memfd exceeding 2 GiB fail. 2. FMODE_LSEEK, FMODE_PREAD, and FMODE_PWRITE are set on the file. This makes sure the file is seekable and can be used with pread() and pwrite(). 3. Initializes the security field for the inode and makes sure that inode creation is permitted by the security module. Currently, none of those things are done. This means writes above 2 GiB fail, pread(), and pwrite() fail, and so on. lseek() happens to work because file_init_path() sets it because shmem defines fop->llseek. Fix this by using memfd_alloc_file() to get the file to make sure the initialization sequence for normal and preserved memfd is the same. Link: https://lkml.kernel.org/r/20260122151842.4069702-3-pratyush@kernel.org Fixes: b3749f174d68 ("mm: memfd_luo: allow preserving memfd") Signed-off-by: Pratyush Yadav (Google) Reviewed-by: Mike Rapoport (Microsoft) Reviewed-by: Pasha Tatashin Cc: Baolin Wang Cc: Hugh Dickins Signed-off-by: Andrew Morton --- mm/memfd_luo.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c index 4f6ba63b43105..01a72e4d3ef69 100644 --- a/mm/memfd_luo.c +++ b/mm/memfd_luo.c @@ -78,6 +78,7 @@ #include #include #include +#include #include "internal.h" static int memfd_luo_preserve_folios(struct file *file, @@ -443,8 +444,7 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args) if (!ser) return -EINVAL; - file = shmem_file_setup("", 0, VM_NORESERVE); - + file = memfd_alloc_file("", 0); if (IS_ERR(file)) { pr_err("failed to setup file: %pe\n", file); return PTR_ERR(file); -- 2.47.3