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