** Tags removed: verification-needed-xenial ** Tags added: verification-done-xenial
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1775326 Title: The kernel NULL pointer dereference happens when accessing the task_struct by task_cpu() in function cpuacct_charge() Status in linux package in Ubuntu: Incomplete Status in linux source package in Xenial: Fix Committed Bug description: [Impact] In function cpuacct_charge(), the NULL pointer dereference happens with the stack pointer being zero inside the task_struct when the task_cpu() is trying to access the member CPU of the struct thread_info inside the stack. It's a use-after-free corruption happening in the situation that the task_struct is released almost concurrently before accessing the task_struct->stack. void cpuacct_charge(struct task_struct *tsk, u64 cputime) { struct cpuacct *ca; int cpu; cpu = task_cpu(tsk); rcu_read_lock(); ca = task_ca(tsk); while (true) { u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu); *cpuusage += cputime; ca = parent_ca(ca); if (!ca) break; } rcu_read_unlock(); } BUG: unable to handle kernel NULL pointer dereference at 0000000000000010 IP: [<ffffffff810c3ff4>] cpuacct_charge+0x14/0x40 PGD 0 Oops: 0000 [#1] SMP CPU: 10 PID: 148614 Comm: qemu-system-x86 Tainted: P W OE 4.4.0-45-generic #66~14.04.1-Ubuntu Hardware name: Dell Inc. PowerEdge R630/02C2CP, BIOS 2.1.7 06/16/2016 task: ffff881ff0f01b80 ti: ffff88018fd70000 task.ti: ffff88018fd70000 RIP: 0010:[<ffffffff810c3ff4>] [<ffffffff810c3ff4>] cpuacct_charge+0x14/0x40 RSP: 0018:ffff88018fd73d10 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff8801931e8000 RCX: ffff88010caff200 RDX: ffff880124508000 RSI: 0066f757398831d6 RDI: ffff8801931e7fa0 RBP: ffff88018fd73d10 R08: ffffffffc04b8320 R09: 0000000000000001 R10: 0000000000000001 R11: 0000000000000000 R12: 0066f757398831d6 R13: 0066f757398b8997 R14: ffff8801931e7fa0 R15: 0000000000000001 FS: 00007f162aaf7700(0000) GS:ffff881ffe740000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000010 CR3: 000000011d86e000 CR4: 00000000003426e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: ffff88018fd73d28 ffffffff810b1a9f ffff8801931e8000 ffff88018fd73d40 ffffffffc069df72 ffff8801931e8000 ffff88018fd73da8 ffffffffc069f121 ffff881ff0f01b80 0000000000000000 ffff881ff0f01b80 ffffffff810bddc0 Call Trace: [<ffffffff810b1a9f>] update_curr+0xdf/0x170 [<ffffffffc069df72>] kvm_vcpu_check_block+0x12/0x60 [kvm] [<ffffffffc069f121>] kvm_vcpu_block+0x191/0x2d0 [kvm] [<ffffffff810bddc0>] ? prepare_to_wait_event+0xf0/0xf0 [<ffffffffc06bb9ee>] kvm_arch_vcpu_ioctl_run+0x17e/0x3d0 [kvm] [<ffffffffc06a1f8b>] kvm_vcpu_ioctl+0x2ab/0x640 [kvm] [<ffffffff81174517>] ? perf_event_context_sched_in+0x87/0xa0 [<ffffffff81210d6d>] do_vfs_ioctl+0x2dd/0x4c0 [<ffffffff8111fa1f>] ? __audit_syscall_entry+0xaf/0x100 [<ffffffff81003176>] ? do_audit_syscall_entry+0x66/0x70 [<ffffffff81210fc9>] SyS_ioctl+0x79/0x90 [<ffffffff817fa4f6>] entry_SYSCALL_64_fastpath+0x16/0x75 Code: 9a 11 00 5b 48 c7 c0 f4 ff ff ff 5d eb df 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 8b 47 08 48 8b 97 78 07 00 00 48 89 e5 <48> 63 48 10 48 8b 52 60 48 8b 82 b8 00 00 00 48 03 04 cd c0 7a RIP [<ffffffff810c3ff4>] cpuacct_charge+0x14/0x40 RSP <ffff88018fd73d10> CR2: 0000000000000010 ---[ end trace 419a30375d0e4622 ]--- [Fix] The patch uses this_cpu_ptr() instead of getting the CPU number by task_cpu() and proceeds to get the cpu_usage by per_cpu_ptr(). And that can avoid accessing the thread_info inside the stack. commit 73e6aafd9ea81498d31361f01db84a0118da2d1c Author: Zhao Lei <zhao...@cn.fujitsu.com> Date: Thu Mar 17 12:19:43 2016 +0800 sched/cpuacct: Simplify the cpuacct code - Use for() instead of while() loop in some functions to make the code simpler. - Use this_cpu_ptr() instead of per_cpu_ptr() to make the code cleaner and a bit faster. Suggested-by: Peter Zijlstra <pet...@infradead.org> Signed-off-by: Zhao Lei <zhao...@cn.fujitsu.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Tejun Heo <hte...@gmail.com> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/d8a7ef9592f55224630cb26dea239f05b6398a4e.1458187654.git.zhao...@cn.fujitsu.com Signed-off-by: Ingo Molnar <mi...@kernel.org> [Test] The test kernel has been tested by the Qemu and cannot be reproduced. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1775326/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
