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32c9625638
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 <daniel@thingy.jp> Acked-by: Lorenzo Stoakes <ljs@kernel.org> Cc: "Liam R. Howlett" <liam@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>