On Wed, Oct 06, 2021 at 05:33:47PM +0800, Hao Sun wrote: > C reproducer: https://drive.google.com/file/d/1RzAsyIZzw5X_m340nY9fu4KWjGdG98pv/view?usp=sharing It's easier than this reproducer makes it look. res = syscall(__NR_openat, -1, 0x20000080ul, 0x4c003ul, 0x10ul); syscall(__NR_finit_module, r[0], 0ul, 3ul); should be enough. Basically, userspace opens an fd without FMODE_READ and passes it to finit_module(). > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 28082 at fs/read_write.c:429 > __kernel_read+0x3bb/0x410 fs/read_write.c:429 > Modules linked in: > CPU: 1 PID: 28082 Comm: syz-executor Not tainted 5.15.0-rc3+ #21 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 > RIP: 0010:__kernel_read+0x3bb/0x410 fs/read_write.c:429 > Call Trace: > kernel_read+0x47/0x60 fs/read_write.c:461 > kernel_read_file+0x20a/0x370 fs/kernel_read_file.c:93 > kernel_read_file_from_fd+0x55/0x90 fs/kernel_read_file.c:184 > __do_sys_finit_module+0x89/0x110 kernel/module.c:4180 finit_module() is not the only caller of kernel_read_file_from_fd() which passes it a fd that userspace passed in, for example kexec_file_load() doesn't validate the fd either. We could validate the fd in individual syscalls, in kernel_read_file_from_fd() or just do what vfs_read() does and return -EBADF without warning. So, one of these two patches. Christoph, Al, what's your preference? diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c index 87aac4c72c37..1f28b693d1db 100644 --- a/fs/kernel_read_file.c +++ b/fs/kernel_read_file.c @@ -178,7 +178,7 @@ int kernel_read_file_from_fd(int fd, loff_t offset, void **buf, struct fd f = fdget(fd); int ret = -EBADF; - if (!f.file) + if (!f.file || !(file->f_mode & FMODE_READ)) goto out; ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id); diff --git a/fs/read_write.c b/fs/read_write.c index af057c57bdc6..bab43b8532d1 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -426,8 +426,8 @@ ssize_t __kernel_read(struct file *file, void *buf, size_t count, loff_t *pos) struct iov_iter iter; ssize_t ret; - if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ))) - return -EINVAL; + if (!(file->f_mode & FMODE_READ)) + return -EBADF; if (!(file->f_mode & FMODE_CAN_READ)) return -EINVAL; /*
