On Wed, Apr 01, 2020 at 12:24:01PM +0200, Marco Elver wrote: > On Wed, 1 Apr 2020 at 09:04, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > > > On Tue, Mar 31, 2020 at 10:27 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > > > > > On Tue, Mar 31, 2020 at 12:35:13PM -0700, syzbot wrote: > > > > Hello, > > > > > > > > syzbot found the following crash on: > > > > > > > > HEAD commit: b12d66a6 mm, kcsan: Instrument SLAB free with ASSERT_EXCLU.. > > > > git tree: https://github.com/google/ktsan.git kcsan > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=111f0865e00000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=10bc0131c4924ba9 > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=6a6bca8169ffda8ce77b > > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > > > > > Unfortunately, I don't have any reproducer for this crash yet. > > > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > > Reported-by: syzbot+6a6bca8169ffda8ce77b@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > ================================================================== > > > > BUG: KCSAN: data-race in glue_cbc_decrypt_req_128bit / glue_cbc_decrypt_req_128bit > > > > > > > > write to 0xffff88809966e128 of 8 bytes by task 24119 on cpu 0: > > > > u128_xor include/crypto/b128ops.h:67 [inline] > > > > glue_cbc_decrypt_req_128bit+0x396/0x460 arch/x86/crypto/glue_helper.c:144 > > > > cbc_decrypt+0x26/0x40 arch/x86/crypto/serpent_avx2_glue.c:152 > > > > crypto_skcipher_decrypt+0x65/0x90 crypto/skcipher.c:652 > > > > _skcipher_recvmsg crypto/algif_skcipher.c:142 [inline] > > > > skcipher_recvmsg+0x7fa/0x8c0 crypto/algif_skcipher.c:161 > > > > skcipher_recvmsg_nokey+0x5e/0x80 crypto/algif_skcipher.c:279 > > > > sock_recvmsg_nosec net/socket.c:886 [inline] > > > > sock_recvmsg net/socket.c:904 [inline] > > > > sock_recvmsg+0x92/0xb0 net/socket.c:900 > > > > ____sys_recvmsg+0x167/0x3a0 net/socket.c:2566 > > > > ___sys_recvmsg+0xb2/0x100 net/socket.c:2608 > > > > __sys_recvmsg+0x9d/0x160 net/socket.c:2642 > > > > __do_sys_recvmsg net/socket.c:2652 [inline] > > > > __se_sys_recvmsg net/socket.c:2649 [inline] > > > > __x64_sys_recvmsg+0x51/0x70 net/socket.c:2649 > > > > do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294 > > > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > > > > > read to 0xffff88809966e128 of 8 bytes by task 24118 on cpu 1: > > > > u128_xor include/crypto/b128ops.h:67 [inline] > > > > glue_cbc_decrypt_req_128bit+0x37c/0x460 arch/x86/crypto/glue_helper.c:144 > > > > cbc_decrypt+0x26/0x40 arch/x86/crypto/serpent_avx2_glue.c:152 > > > > crypto_skcipher_decrypt+0x65/0x90 crypto/skcipher.c:652 > > > > _skcipher_recvmsg crypto/algif_skcipher.c:142 [inline] > > > > skcipher_recvmsg+0x7fa/0x8c0 crypto/algif_skcipher.c:161 > > > > skcipher_recvmsg_nokey+0x5e/0x80 crypto/algif_skcipher.c:279 > > > > sock_recvmsg_nosec net/socket.c:886 [inline] > > > > sock_recvmsg net/socket.c:904 [inline] > > > > sock_recvmsg+0x92/0xb0 net/socket.c:900 > > > > ____sys_recvmsg+0x167/0x3a0 net/socket.c:2566 > > > > ___sys_recvmsg+0xb2/0x100 net/socket.c:2608 > > > > __sys_recvmsg+0x9d/0x160 net/socket.c:2642 > > > > __do_sys_recvmsg net/socket.c:2652 [inline] > > > > __se_sys_recvmsg net/socket.c:2649 [inline] > > > > __x64_sys_recvmsg+0x51/0x70 net/socket.c:2649 > > > > do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294 > > > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > > > > > Reported by Kernel Concurrency Sanitizer on: > > > > CPU: 1 PID: 24118 Comm: syz-executor.1 Not tainted 5.6.0-rc1-syzkaller #0 > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > > ================================================================== > > > > > > > > > > I think this is a problem for almost all the crypto code. Due to AF_ALG, both > > > the source and destination buffers can be userspace pages that were gotten with > > > get_user_pages(). Such pages can be concurrently modified, not just by the > > > kernel but also by userspace. > > > > > > I'm not sure what can be done about this. > > > > Oh, I thought it's something more serious like a shared crypto object. > > Thanks for debugging. > > I think I've seen this before in another context (b/149818448): > > > > BUG: KCSAN: data-race in copyin / copyin > > > > write to 0xffff888103c8b000 of 4096 bytes by task 20917 on cpu 0: > > instrument_copy_from_user include/linux/instrumented.h:106 [inline] > > copyin+0xab/0xc0 lib/iov_iter.c:151 > > copy_page_from_iter_iovec lib/iov_iter.c:296 [inline] > > copy_page_from_iter+0x23f/0x5f0 lib/iov_iter.c:942 > > process_vm_rw_pages mm/process_vm_access.c:46 [inline] > > process_vm_rw_single_vec mm/process_vm_access.c:120 [inline] > > process_vm_rw_core.isra.0+0x448/0x820 mm/process_vm_access.c:218 > > process_vm_rw+0x1c4/0x1e0 mm/process_vm_access.c:286 > > __do_sys_process_vm_writev mm/process_vm_access.c:308 [inline] > > __se_sys_process_vm_writev mm/process_vm_access.c:303 [inline] > > __x64_sys_process_vm_writev+0x8b/0xb0 mm/process_vm_access.c:303 > > do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294 > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > write to 0xffff888103c8b000 of 4096 bytes by task 20918 on cpu 1: > > instrument_copy_from_user include/linux/instrumented.h:106 [inline] > > copyin+0xab/0xc0 lib/iov_iter.c:151 > > copy_page_from_iter_iovec lib/iov_iter.c:296 [inline] > > copy_page_from_iter+0x23f/0x5f0 lib/iov_iter.c:942 > > process_vm_rw_pages mm/process_vm_access.c:46 [inline] > > process_vm_rw_single_vec mm/process_vm_access.c:120 [inline] > > process_vm_rw_core.isra.0+0x448/0x820 mm/process_vm_access.c:218 > > process_vm_rw+0x1c4/0x1e0 mm/process_vm_access.c:286 > > __do_sys_process_vm_writev mm/process_vm_access.c:308 [inline] > > __se_sys_process_vm_writev mm/process_vm_access.c:303 [inline] > > __x64_sys_process_vm_writev+0x8b/0xb0 mm/process_vm_access.c:303 > > do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294 > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > > > Marco, I think we need to ignore all memory that comes from > > get_user_pages() somehow. Either not set watchpoints at all, or > > perhaps filter them out later if the check is not totally free. > > Makes sense. We already have similar checks, and they're in the > slow-path, so it shouldn't be a problem. Let me investigate. > I'm wondering whether you really should move so soon to ignoring these races? They are still races; the crypto code is doing standard unannotated reads/writes of memory that can be concurrently modified. The issue is that fixing it would require adding READ_ONCE() / WRITE_ONCE() in hundreds of different places, affecting most crypto-related .c files. Generally, since encryption and hash algorithms are designed to handle arbitrary data anyway, getting different values on each read won't crash the code. So hopefully this isn't a "real" problem. But it's still undefined behavior. - Eric
