Hide Forgot
There is a race condition problem ok poll_refs which could result in a NULL pointer dereference. The crash trace is like: ********* KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 0 PID: 30781 Comm: syz-executor.2 Not tainted 6.0.0-g493ffd6605b2 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 RIP: 0010:io_poll_remove_entry io_uring/poll.c:154 [inline] RIP: 0010:io_poll_remove_entries+0x171/0x5b4 io_uring/poll.c:190 Code: ... RSP: 0018:ffff88810dfefba0 EFLAGS: 00010202 RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000040000 RDX: ffffc900030c4000 RSI: 000000000003ffff RDI: 0000000000040000 RBP: 0000000000000008 R08: ffffffff9764d3dd R09: fffffbfff3836781 R10: fffffbfff3836781 R11: 0000000000000000 R12: 1ffff11003422d60 R13: ffff88801a116b04 R14: ffff88801a116ac0 R15: dffffc0000000000 FS: 00007f9c07497700(0000) GS:ffff88811a600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ffb5c00ea98 CR3: 0000000105680005 CR4: 0000000000770ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> io_apoll_task_func+0x3f/0xa0 io_uring/poll.c:299 handle_tw_list io_uring/io_uring.c:1037 [inline] tctx_task_work+0x37e/0x4f0 io_uring/io_uring.c:1090 task_work_run+0x13a/0x1b0 kernel/task_work.c:177 get_signal+0x2402/0x25a0 kernel/signal.c:2635 arch_do_signal_or_restart+0x3b/0x660 arch/x86/kernel/signal.c:869 exit_to_user_mode_loop kernel/entry/common.c:166 [inline] exit_to_user_mode_prepare+0xc2/0x160 kernel/entry/common.c:201 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline] syscall_exit_to_user_mode+0x58/0x160 kernel/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x63/0xcd ********** Reference: https://github.com/torvalds/linux/commit/12ad3d2d6c5b0131a6052de91360849e3e154846 https://github.com/torvalds/linux/commit/a26a35e9019fd70bf3cf647dcfdae87abc7bacea
The root cause for this is a tiny overlooking in io_poll_check_events() when cocurrently run with poll cancel routine io_poll_cancel_req(). The interleaving to trigger use-after-free: CPU0 | CPU1 | io_apoll_task_func() | io_poll_cancel_req() io_poll_check_events() | // do while first loop | v = atomic_read(...) | // v = poll_refs = 1 | ... | io_poll_mark_cancelled() | atomic_or() | // poll_refs = IO_POLL_CANCEL_FLAG | 1 | atomic_sub_return(...) | // poll_refs = IO_POLL_CANCEL_FLAG | // loop continue | | | io_poll_execute() | io_poll_get_ownership() | // poll_refs = IO_POLL_CANCEL_FLAG | 1 | // gets the ownership v = atomic_read(...) | // poll_refs not change | | if (v & IO_POLL_CANCEL_FLAG) | return -ECANCELED; | // io_poll_check_events return | // will go into | // io_req_complete_failed() free req | | | io_apoll_task_func() | // also go into io_req_complete_failed() And the interleaving to trigger the kernel WARNING: CPU0 | CPU1 | io_apoll_task_func() | io_poll_cancel_req() io_poll_check_events() | // do while first loop | v = atomic_read(...) | // v = poll_refs = 1 | ... | io_poll_mark_cancelled() | atomic_or() | // poll_refs = IO_POLL_CANCEL_FLAG | 1 | atomic_sub_return(...) | // poll_refs = IO_POLL_CANCEL_FLAG | // loop continue | | v = atomic_read(...) | // v = IO_POLL_CANCEL_FLAG | | io_poll_execute() | io_poll_get_ownership() | // poll_refs = IO_POLL_CANCEL_FLAG | 1 | // gets the ownership | WARN_ON_ONCE(!(v & IO_POLL_REF_MASK))) | // v & IO_POLL_REF_MASK = 0 WARN | | | io_apoll_task_func() | // also go into io_req_complete_failed()
There was no shipped kernel version were seen affected with this problem. These files are not built in our source code.
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s): https://access.redhat.com/security/cve/cve-2023-0468