On Wed, Oct 06, 2021 at 01:17:32PM +0100, Matthew Wilcox wrote: > 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? I think the warning was something Linux wanted. So the first one seems like the way to go.
