#include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * We don't expose the real in-memory order of objects for security reasons. * But still the comparison results should be suitable for sorting. So we * obfuscate kernel pointers values and compare the production instead. * * The obfuscation is done in two steps. First we xor the kernel pointer with * a random value, which puts pointer into a new position in a reordered space. * Secondly we multiply the xor production with a large odd random number to * permute its bits even more (the odd multiplier guarantees that the product * is unique ever after the high bits are truncated, since any odd number is * relative prime to 2^n). * * Note also that the obfuscation itself is invisible to userspace and if needed * it can be changed to an alternate scheme. */ static unsigned long cookies[KCMP_TYPES][2] __read_mostly; static long kptr_obfuscate(long v, int type) { return (v ^ cookies[type][0]) * cookies[type][1]; } /* * 0 - equal, i.e. v1 = v2 * 1 - less than, i.e. v1 < v2 * 2 - greater than, i.e. v1 > v2 * 3 - not equal but ordering unavailable (reserved for future) */ static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type) { long t1, t2; t1 = kptr_obfuscate((long)v1, type); t2 = kptr_obfuscate((long)v2, type); return (t1 < t2) | ((t1 > t2) << 1); } /* The caller must have pinned the task */ static struct file * get_file_raw_ptr(struct task_struct *task, unsigned int idx) { struct file *file = NULL; task_lock(task); rcu_read_lock(); if (task->files) file = fcheck_files(task->files, idx); rcu_read_unlock(); task_unlock(task); return file; } static void kcmp_unlock(struct mutex *m1, struct mutex *m2) { if (likely(m2 != m1)) mutex_unlock(m2); mutex_unlock(m1); } static int kcmp_lock(struct mutex *m1, struct mutex *m2) { int err; if (m2 > m1) swap(m1, m2); err = mutex_lock_killable(m1); if (!err && likely(m1 != m2)) { err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING); if (err) mutex_unlock(m1); } return err; } SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, unsigned long, idx1, unsigned long, idx2) { struct task_struct *task1, *task2; int ret; rcu_read_lock(); /* * Tasks are looked up in caller's PID namespace only. */ task1 = find_task_by_vpid(pid1); task2 = find_task_by_vpid(pid2); if (!task1 || !task2) goto err_no_task; get_task_struct(task1); get_task_struct(task2); rcu_read_unlock(); /* * One should have enough rights to inspect task details. */ ret = kcmp_lock(&task1->signal->cred_guard_mutex, &task2->signal->cred_guard_mutex); if (ret) goto err; if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) || !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) { ret = -EPERM; goto err_unlock; } switch (type) { case KCMP_FILE: { struct file *filp1, *filp2; filp1 = get_file_raw_ptr(task1, idx1); filp2 = get_file_raw_ptr(task2, idx2); if (filp1 && filp2) ret = kcmp_ptr(filp1, filp2, KCMP_FILE); else ret = -EBADF; break; } case KCMP_VM: ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM); break; case KCMP_FILES: ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES); break; case KCMP_FS: ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS); break; case KCMP_SIGHAND: ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND); break; case KCMP_IO: ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO); break; case KCMP_SYSVSEM: #ifdef CONFIG_SYSVIPC ret = kcmp_ptr(task1->sysvsem.undo_list, task2->sysvsem.undo_list, KCMP_SYSVSEM); #else ret = -EOPNOTSUPP; #endif break; default: ret = -EINVAL; break; } err_unlock: kcmp_unlock(&task1->signal->cred_guard_mutex, &task2->signal->cred_guard_mutex); err: put_task_struct(task1); put_task_struct(task2); return ret; err_no_task: rcu_read_unlock(); return -ESRCH; } static __init int kcmp_cookies_init(void) { int i; get_random_bytes(cookies, sizeof(cookies)); for (i = 0; i < KCMP_TYPES; i++) cookies[i][1] |= (~(~0UL >> 1) | 1); return 0; } arch_initcall(kcmp_cookies_init);
authorBob Liu <bob.liu@oracle.com>2016-06-07 10:43:15 -0400
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2016-06-08 13:54:39 -0400
commitefd1535270c1deb0487527bf0c3c827301a69c93 (patch)
treee0afb0ad9d8e7db1ed1d52ba4c07e2278ff2b7c4 /Documentation/debugging-via-ohci1394.txt
parent116f7d4a21fe450efc652c4850eb27cda36c9db0 (diff)
xen-blkfront: don't call talk_to_blkback when already connected to blkback
Sometimes blkfront may twice receive blkback_changed() notification (XenbusStateConnected) after migration, which will cause talk_to_blkback() to be called twice too and confuse xen-blkback. The flow is as follow: blkfront blkback blkfront_resume() > talk_to_blkback() > Set blkfront to XenbusStateInitialised front changed() > Connect() > Set blkback to XenbusStateConnected blkback_changed() > Skip talk_to_blkback() because frontstate == XenbusStateInitialised > blkfront_connect() > Set blkfront to XenbusStateConnected ----- And here we get another XenbusStateConnected notification leading to: ----- blkback_changed() > because now frontstate != XenbusStateInitialised talk_to_blkback() is also called again > blkfront state changed from XenbusStateConnected to XenbusStateInitialised (Which is not correct!) front_changed(): > Do nothing because blkback already in XenbusStateConnected Now blkback is in XenbusStateConnected but blkfront is still in XenbusStateInitialised - leading to no disks. Poking of the XenbusStateConnected state is allowed (to deal with block disk change) and has to be dealt with. The most likely cause of this bug are custom udev scripts hooking up the disks and then validating the size. Signed-off-by: Bob Liu <bob.liu@oracle.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Diffstat (limited to 'Documentation/debugging-via-ohci1394.txt')