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 t1, t2; 48 49 t1 = kptr_obfuscate((long)v1, type); 50 t2 = kptr_obfuscate((long)v2, type); 51 52 return (t1 < t2) | ((t1 > t2) << 1); 53 } 54 55 /* The caller must have pinned the task */ 56 static struct file * 57 get_file_raw_ptr(struct task_struct *task, unsigned int idx) 58 { 59 struct file *file = NULL; 60 61 task_lock(task); 62 rcu_read_lock(); 63 64 if (task->files) 65 file = fcheck_files(task->files, idx); 66 67 rcu_read_unlock(); 68 task_unlock(task); 69 70 return file; 71 } 72 73 static void kcmp_unlock(struct mutex *m1, struct mutex *m2) 74 { 75 if (likely(m2 != m1)) 76 mutex_unlock(m2); 77 mutex_unlock(m1); 78 } 79 80 static int kcmp_lock(struct mutex *m1, struct mutex *m2) 81 { 82 int err; 83 84 if (m2 > m1) 85 swap(m1, m2); 86 87 err = mutex_lock_killable(m1); 88 if (!err && likely(m1 != m2)) { 89 err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING); 90 if (err) 91 mutex_unlock(m1); 92 } 93 94 return err; 95 } 96 97 SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, 98 unsigned long, idx1, unsigned long, idx2) 99 { 100 struct task_struct *task1, *task2; 101 int ret; 102 103 rcu_read_lock(); 104 105 /* 106 * Tasks are looked up in caller's PID namespace only. 107 */ 108 task1 = find_task_by_vpid(pid1); 109 task2 = find_task_by_vpid(pid2); 110 if (!task1 || !task2) 111 goto err_no_task; 112 113 get_task_struct(task1); 114 get_task_struct(task2); 115 116 rcu_read_unlock(); 117 118 /* 119 * One should have enough rights to inspect task details. 120 */ 121 ret = kcmp_lock(&task1->signal->cred_guard_mutex, 122 &task2->signal->cred_guard_mutex); 123 if (ret) 124 goto err; 125 if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) || 126 !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) { 127 ret = -EPERM; 128 goto err_unlock; 129 } 130 131 switch (type) { 132 case KCMP_FILE: { 133 struct file *filp1, *filp2; 134 135 filp1 = get_file_raw_ptr(task1, idx1); 136 filp2 = get_file_raw_ptr(task2, idx2); 137 138 if (filp1 && filp2) 139 ret = kcmp_ptr(filp1, filp2, KCMP_FILE); 140 else 141 ret = -EBADF; 142 break; 143 } 144 case KCMP_VM: 145 ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM); 146 break; 147 case KCMP_FILES: 148 ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES); 149 break; 150 case KCMP_FS: 151 ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS); 152 break; 153 case KCMP_SIGHAND: 154 ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND); 155 break; 156 case KCMP_IO: 157 ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO); 158 break; 159 case KCMP_SYSVSEM: 160 #ifdef CONFIG_SYSVIPC 161 ret = kcmp_ptr(task1->sysvsem.undo_list, 162 task2->sysvsem.undo_list, 163 KCMP_SYSVSEM); 164 #else 165 ret = -EOPNOTSUPP; 166 #endif 167 break; 168 default: 169 ret = -EINVAL; 170 break; 171 } 172 173 err_unlock: 174 kcmp_unlock(&task1->signal->cred_guard_mutex, 175 &task2->signal->cred_guard_mutex); 176 err: 177 put_task_struct(task1); 178 put_task_struct(task2); 179 180 return ret; 181 182 err_no_task: 183 rcu_read_unlock(); 184 return -ESRCH; 185 } 186 187 static __init int kcmp_cookies_init(void) 188 { 189 int i; 190 191 get_random_bytes(cookies, sizeof(cookies)); 192 193 for (i = 0; i < KCMP_TYPES; i++) 194 cookies[i][1] |= (~(~0UL >> 1) | 1); 195 196 return 0; 197 } 198 arch_initcall(kcmp_cookies_init); 199