From: "Matthew Wilcox (Oracle)" willy@infradead.org Subject: vfs: check fd has read access in kernel_read_file_from_fd()

If we open a file without read access and then pass the fd to a syscall whose implementation calls kernel_read_file_from_fd(), we get a warning from __kernel_read():

if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ)))

This currently affects both finit_module() and kexec_file_load(), but it could affect other syscalls in the future.

Link: https://lkml.kernel.org/r/20211007220110.600005-1-willy@infradead.org Fixes: b844f0ecbc56 ("vfs: define kernel_copy_file_from_fd()") Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Reported-by: Hao Sun sunhao.th@gmail.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Christian Brauner christian.brauner@ubuntu.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Mimi Zohar zohar@linux.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/kernel_read_file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/kernel_read_file.c~vfs-check-fd-has-read-access-in-kernel_read_file_from_fd +++ a/fs/kernel_read_file.c @@ -178,7 +178,7 @@ int kernel_read_file_from_fd(int fd, lof struct fd f = fdget(fd); int ret = -EBADF;

- if (!f.file) + if (!f.file || !(f.file->f_mode & FMODE_READ)) goto out;

ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id); _