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. - Eric
