On Mon, Feb 06, 2023 at 10:58:05PM +0800, Zhong Jinghua wrote: > We tested and found an alarm caused by nbd_ioctl arg without verification. > The UBSAN warning calltrace like below: > > UBSAN: Undefined behaviour in fs/buffer.c:1709:35 > signed integer overflow: > -9223372036854775808 - 1 cannot be represented in type 'long long int' > CPU: 3 PID: 2523 Comm: syz-executor.0 Not tainted 4.19.90 #1 > Hardware name: linux,dummy-virt (DT) > Call trace: > dump_backtrace+0x0/0x3f0 arch/arm64/kernel/time.c:78 > show_stack+0x28/0x38 arch/arm64/kernel/traps.c:158 > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x170/0x1dc lib/dump_stack.c:118 > ubsan_epilogue+0x18/0xb4 lib/ubsan.c:161 > handle_overflow+0x188/0x1dc lib/ubsan.c:192 > __ubsan_handle_sub_overflow+0x34/0x44 lib/ubsan.c:206 > __block_write_full_page+0x94c/0xa20 fs/buffer.c:1709 > block_write_full_page+0x1f0/0x280 fs/buffer.c:2934 > blkdev_writepage+0x34/0x40 fs/block_dev.c:607 > __writepage+0x68/0xe8 mm/page-writeback.c:2305 > write_cache_pages+0x44c/0xc70 mm/page-writeback.c:2240 > generic_writepages+0xdc/0x148 mm/page-writeback.c:2329 > blkdev_writepages+0x2c/0x38 fs/block_dev.c:2114 > do_writepages+0xd4/0x250 mm/page-writeback.c:2344 > > The reason for triggering this warning is __block_write_full_page() > -> i_size_read(inode) - 1 overflow. > inode->i_size is assigned in __nbd_ioctl() -> nbd_set_size() -> bytesize. > We think it is necessary to limit the size of arg to prevent errors. > > Moreover, __nbd_ioctl() -> nbd_add_socket(), arg will be cast to int. > Assuming the value of arg is 0x80000000000000001) (on a 64-bit machine), > it will become 1 after the coercion, which will return unexpected results. > > Fix it by adding checks to prevent passing in too large numbers. > > Signed-off-by: Zhong Jinghua <zhongjinghua@xxxxxxxxxx> Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx> Thanks, Josef
