Hello, The following program triggers use-after-free in sock_wake_async:
// autogenerated by syzkaller (http://github.com/google/syzkaller) #include <syscall.h> #include <string.h> #include <stdint.h> #include <pthread.h> long r2 = -1; long r3 = -1; long r7 = -1; void *thr0(void *arg) { syscall(SYS_splice, r2, 0x0ul, r7, 0x0ul, 0x4ul, 0x8ul); return 0; } void *thr1(void *arg) { syscall(SYS_close, r2, 0, 0, 0, 0, 0); return 0; } void *thr2(void *arg) { syscall(SYS_write, r3, 0x20003000ul, 0xe7ul, 0, 0, 0); return 0; } int main() { long r0 = syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x3ul, 0x32ul, 0xfffffffffffffffful, 0x0ul); long r1 = syscall(SYS_socketpair, 0x1ul, 0x1ul, 0x0ul, 0x20000000ul, 0, 0); r2 = *(uint32_t*)0x20000000; r3 = *(uint32_t*)0x20000004; *(uint64_t*)0x20001000 = 0x4; long r5 = syscall(SYS_ioctl, r2, 0x5452ul, 0x20001000ul, 0, 0, 0); long r6 = syscall(SYS_pipe2, 0x20002000ul, 0x80800ul, 0, 0, 0, 0); r7 = *(uint32_t*)0x20002004; pthread_t th[3]; pthread_create(&th[0], 0, thr0, 0); pthread_create(&th[1], 0, thr1, 0); pthread_create(&th[2], 0, thr2, 0); pthread_join(th[0], 0); pthread_join(th[1], 0); pthread_join(th[2], 0); return 0; } The use-after-free fires after a minute of running it in a tight parallel loop. I use the stress utility for this: $ go get golang.org/x/tools/cmd/stress $ stress -p 128 -failure "ignore" ./a.out ================================================================== BUG: KASAN: use-after-free in sock_wake_async+0x325/0x340 at addr ffff880061d1ad10 Read of size 8 by task a.out/23178 ============================================================================= BUG sock_inode_cache (Not tainted): kasan: bad access detected ----------------------------------------------------------------------------- Disabling lock debugging due to kernel taint INFO: Allocated in sock_alloc_inode+0x1d/0x220 age=0 cpu=2 pid=23183 [< none >] kmem_cache_alloc+0x1a6/0x1f0 mm/slub.c:2514 [< none >] sock_alloc_inode+0x1d/0x220 net/socket.c:250 [< none >] alloc_inode+0x61/0x180 fs/inode.c:198 [< none >] new_inode_pseudo+0x17/0xe0 fs/inode.c:878 [< none >] sock_alloc+0x3d/0x260 net/socket.c:540 [< none >] __sock_create+0xa7/0x620 net/socket.c:1133 [< inline >] sock_create net/socket.c:1209 [< inline >] SYSC_socketpair net/socket.c:1281 [< none >] SyS_socketpair+0x112/0x4e0 net/socket.c:1260 [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185 INFO: Freed in sock_destroy_inode+0x56/0x70 age=0 cpu=2 pid=23185 [< none >] kmem_cache_free+0x24e/0x260 mm/slub.c:2742 [< none >] sock_destroy_inode+0x56/0x70 net/socket.c:279 [< none >] destroy_inode+0xc4/0x120 fs/inode.c:255 [< none >] evict+0x36b/0x580 fs/inode.c:559 [< inline >] iput_final fs/inode.c:1477 [< none >] iput+0x4a0/0x790 fs/inode.c:1504 [< inline >] dentry_iput fs/dcache.c:358 [< none >] __dentry_kill+0x4fe/0x700 fs/dcache.c:543 [< inline >] dentry_kill fs/dcache.c:587 [< none >] dput+0x6ab/0x7a0 fs/dcache.c:796 [< none >] __fput+0x3fb/0x6e0 fs/file_table.c:226 [< none >] ____fput+0x15/0x20 fs/file_table.c:244 [< none >] task_work_run+0x163/0x1f0 kernel/task_work.c:115 (discriminator 1) [< inline >] tracehook_notify_resume include/linux/tracehook.h:191 [< none >] exit_to_usermode_loop+0x180/0x1a0 arch/x86/entry/common.c:251 [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:282 [< none >] syscall_return_slowpath+0x19f/0x210 arch/x86/entry/common.c:344 [< none >] int_ret_from_sys_call+0x25/0x9f arch/x86/entry/entry_64.S:281 INFO: Slab 0xffffea0001874600 objects=25 used=2 fp=0xffff880061d1c100 flags=0x500000000004080 INFO: Object 0xffff880061d1ad00 @offset=11520 fp=0xffff880061d1a300 CPU: 3 PID: 23178 Comm: a.out Tainted: G B 4.4.0-rc1+ #84 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 00000000ffffffff ffff880061baf8f0 ffffffff825d3336 ffff88003e0dc280 ffff880061d1ad00 ffff880061d18000 ffff880061baf920 ffffffff81618784 ffff88003e0dc280 ffffea0001874600 ffff880061d1ad00 00000000000000e7 Call Trace: [<ffffffff8162135e>] __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:280 [< inline >] __read_once_size include/linux/compiler.h:218 [<ffffffff83dcda05>] sock_wake_async+0x325/0x340 net/socket.c:1068 [< inline >] sk_wake_async include/net/sock.h:2011 [<ffffffff83ddb414>] sock_def_readable+0x1e4/0x290 net/core/sock.c:2312 [<ffffffff84188bdb>] unix_stream_sendmsg+0x4db/0x930 net/unix/af_unix.c:1864 [< inline >] sock_sendmsg_nosec net/socket.c:610 [<ffffffff83dcb1fa>] sock_sendmsg+0xca/0x110 net/socket.c:620 [<ffffffff83dcb456>] sock_write_iter+0x216/0x3a0 net/socket.c:819 [< inline >] new_sync_write fs/read_write.c:478 [<ffffffff8165d310>] __vfs_write+0x300/0x470 fs/read_write.c:491 [<ffffffff8165e4fe>] vfs_write+0x16e/0x490 fs/read_write.c:538 [< inline >] SYSC_write fs/read_write.c:585 [<ffffffff81661141>] SyS_write+0x111/0x220 fs/read_write.c:577 [<ffffffff84bf0c36>] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185 ================================================================== I am on commit 8005c49d9aea74d382f474ce11afbbc7d7130bec (Nov 15) but also merged in 7d267278a9ece963d77eefec61630223fce08c6c (unix: avoid use-after-free in ep_remove_wait_queue) from net repo. 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