1 #include <linux/kernel.h> 2 #include <linux/syscalls.h> 3 #include <linux/fdtable.h> 4 #include <linux/string.h> 5 #include <linux/random.h> 6 #include <linux/module.h> 7 #include <linux/ptrace.h> 8 #include <linux/init.h> 9 #include <linux/errno.h> 10 #include <linux/cache.h> 11 #include <linux/bug.h> 12 #include <linux/err.h> 13 #include <linux/kcmp.h> 14 15 #include <asm/unistd.h> 16 17 /* 18 * We don't expose the real in-memory order of objects for security reasons. 19 * But still the comparison results should be suitable for sorting. So we 20 * obfuscate kernel pointers values and compare the production instead. 21 * 22 * The obfuscation is done in two steps. First we xor the kernel pointer with 23 * a random value, which puts pointer into a new position in a reordered space. 24 * Secondly we multiply the xor production with a large odd random number to 25 * permute its bits even more (the odd multiplier guarantees that the product 26 * is unique ever after the high bits are truncated, since any odd number is 27 * relative prime to 2^n). 28 * 29 * Note also that the obfuscation itself is invisible to userspace and if needed 30 * it can be changed to an alternate scheme. 31 */ 32 static unsigned long cookies[KCMP_TYPES][2] __read_mostly; 33 34 static long kptr_obfuscate(long v, int type) 35 { 36 return (v ^ cookies[type][0]) * cookies[type][1]; 37 } 38 39 /* 40 * 0 - equal, i.e. v1 = v2 41 * 1 - less than, i.e. v1 < v2 42 * 2 - greater than, i.e. v1 > v2 43 * 3 - not equal but ordering unavailable (reserved for future) 44 */ 45 static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type) 46 { 47 long ret; 48 49 ret = kptr_obfuscate((long)v1, type) - kptr_obfuscate((long)v2, type); 50 51 return (ret < 0) | ((ret > 0) << 1); 52 } 53 54 /* The caller must have pinned the task */ 55 static struct file * 56 get_file_raw_ptr(struct task_struct *task, unsigned int idx) 57 { 58 struct file *file = NULL; 59 60 task_lock(task); 61 rcu_read_lock(); 62 63 if (task->files) 64 file = fcheck_files(task->files, idx); 65 66 rcu_read_unlock(); 67 task_unlock(task); 68 69 return file; 70 } 71 72 static void kcmp_unlock(struct mutex *m1, struct mutex *m2) 73 { 74 if (likely(m2 != m1)) 75 mutex_unlock(m2); 76 mutex_unlock(m1); 77 } 78 79 static int kcmp_lock(struct mutex *m1, struct mutex *m2) 80 { 81 int err; 82 83 if (m2 > m1) 84 swap(m1, m2); 85 86 err = mutex_lock_killable(m1); 87 if (!err && likely(m1 != m2)) { 88 err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING); 89 if (err) 90 mutex_unlock(m1); 91 } 92 93 return err; 94 } 95 96 SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, 97 unsigned long, idx1, unsigned long, idx2) 98 { 99 struct task_struct *task1, *task2; 100 int ret; 101 102 rcu_read_lock(); 103 104 /* 105 * Tasks are looked up in caller's PID namespace only. 106 */ 107 task1 = find_task_by_vpid(pid1); 108 task2 = find_task_by_vpid(pid2); 109 if (!task1 || !task2) 110 goto err_no_task; 111 112 get_task_struct(task1); 113 get_task_struct(task2); 114 115 rcu_read_unlock(); 116 117 /* 118 * One should have enough rights to inspect task details. 119 */ 120 ret = kcmp_lock(&task1->signal->cred_guard_mutex, 121 &task2->signal->cred_guard_mutex); 122 if (ret) 123 goto err; 124 if (!ptrace_may_access(task1, PTRACE_MODE_READ) || 125 !ptrace_may_access(task2, PTRACE_MODE_READ)) { 126 ret = -EPERM; 127 goto err_unlock; 128 } 129 130 switch (type) { 131 case KCMP_FILE: { 132 struct file *filp1, *filp2; 133 134 filp1 = get_file_raw_ptr(task1, idx1); 135 filp2 = get_file_raw_ptr(task2, idx2); 136 137 if (filp1 && filp2) 138 ret = kcmp_ptr(filp1, filp2, KCMP_FILE); 139 else 140 ret = -EBADF; 141 break; 142 } 143 case KCMP_VM: 144 ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM); 145 break; 146 case KCMP_FILES: 147 ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES); 148 break; 149 case KCMP_FS: 150 ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS); 151 break; 152 case KCMP_SIGHAND: 153 ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND); 154 break; 155 case KCMP_IO: 156 ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO); 157 break; 158 case KCMP_SYSVSEM: 159 #ifdef CONFIG_SYSVIPC 160 ret = kcmp_ptr(task1->sysvsem.undo_list, 161 task2->sysvsem.undo_list, 162 KCMP_SYSVSEM); 163 #else 164 ret = -EOPNOTSUPP; 165 #endif 166 break; 167 default: 168 ret = -EINVAL; 169 break; 170 } 171 172 err_unlock: 173 kcmp_unlock(&task1->signal->cred_guard_mutex, 174 &task2->signal->cred_guard_mutex); 175 err: 176 put_task_struct(task1); 177 put_task_struct(task2); 178 179 return ret; 180 181 err_no_task: 182 rcu_read_unlock(); 183 return -ESRCH; 184 } 185 186 static __init int kcmp_cookies_init(void) 187 { 188 int i; 189 190 get_random_bytes(cookies, sizeof(cookies)); 191 192 for (i = 0; i < KCMP_TYPES; i++) 193 cookies[i][1] |= (~(~0UL >> 1) | 1); 194 195 return 0; 196 } 197 arch_initcall(kcmp_cookies_init); 198