From 32c9625638c2fda23b9301be5184b8abf84c92a7 Mon Sep 17 00:00:00 2001 From: Daniel Palmer Date: Sat, 23 May 2026 22:04:45 +0900 Subject: [PATCH] tmpfs/ramfs: let memfd_create() work on nommu Currently trying to use memfd_create() on nommu returns an error with errno set to EFBIG. The manpage memfd_create() doesn't have EFBIG as a possible error value. Doing some digging this is coming from 0 getting passed as newsize to ramfs_nommu_expand_for_mapping() and that getting into get_order() and there "The result is undefined if the size is 0". Whatever comes out of get_order() is then used in the following logic and that results in the EFBIG that causes the syscall to fail and the errno in userspace. If newsize is 0 there is nothing to do so just return. Roughly tested on m68k nommu by creating a process, creating an memfd, forking another process, mmap()ing the memfd in the child, writing into the mapping, then mmap()ing in the parent and checking that the right data is there. Link: https://lore.kernel.org/20260523130445.1101818-1-daniel@thingy.jp Signed-off-by: Daniel Palmer Acked-by: Lorenzo Stoakes Cc: "Liam R. Howlett" Cc: Al Viro Cc: Christian Brauner Signed-off-by: Andrew Morton --- fs/ramfs/file-nommu.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c index 2f79bcb89d2e..fb471bf88ab7 100644 --- a/fs/ramfs/file-nommu.c +++ b/fs/ramfs/file-nommu.c @@ -69,6 +69,9 @@ int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize) gfp_t gfp = mapping_gfp_mask(inode->i_mapping); /* make various checks */ + if (!newsize) + return 0; + order = get_order(newsize); if (unlikely(order > MAX_PAGE_ORDER)) return -EFBIG;