1 page.title=Permissions 2 @jd:body 3 4 <div id="qv-wrapper"> 5 <div id="qv"> 6 7 <h2>In this document</h2> 8 <ol> 9 <li><a href="#arch">Security Architecture</a></li> 10 <li><a href="#signing">Application Signing</a></li> 11 <li><a href="#userid">User IDs and File Access</a></li> 12 <li><a href="#permissions">Using Permissions</a></li> 13 <li><a href="#declaring">Declaring and Enforcing Permissions</a> 14 <ol> 15 <li><a href="#manifest">...in AndroidManifest.xml</a></li> 16 <li><a href="#broadcasts">...when Sending Broadcasts</a></li> 17 <li><a href="#enforcement">Other Permission Enforcement</a></li> 18 </ol></li> 19 <li><a href="#uri">URI Permissions</a></li> 20 </ol> 21 </div> 22 </div> 23 <p>This document describes how application developers can use the 24 security features provided by Android. A more general <a 25 href="http://source.android.com/tech/security/index.html"> Android Security 26 Overview</a> is provided in the Android Open Source Project.</p> 27 28 <p>Android is a privilege-separated operating system, in which each 29 application runs with a distinct system identity (Linux user ID and group 30 ID). Parts of the system are also separated into distinct identities. 31 Linux thereby isolates applications from each other and from the system.</p> 32 33 <p>Additional finer-grained security features are provided through a 34 "permission" mechanism that enforces restrictions on the specific operations 35 that a particular process can perform, and per-URI permissions for granting 36 ad-hoc access to specific pieces of data.</p> 37 38 <a name="arch"></a> 39 <h2>Security Architecture</h2> 40 41 <p>A central design point of the Android security architecture is that no 42 application, by default, has permission to perform any operations that would 43 adversely impact other applications, the operating system, or the user. This 44 includes reading or writing the user's private data (such as contacts or 45 e-mails), reading or writing another application's files, performing 46 network access, keeping the device awake, etc.</p> 47 48 <p>Because Android sandboxes applications from each other, applications 49 must explicitly share resources and data. They do this by declaring the 50 <em>permissions</em> they need for additional capabilities not provided by 51 the basic sandbox. Applications statically declare the permissions they 52 require, and the Android system prompts the user for consent at the time the 53 application is installed. Android has no mechanism for granting permissions 54 dynamically (at run-time) because it complicates the user experience to the 55 detriment of security.</p> 56 57 <p>The application sandbox does not depend on the technology used to build 58 an application. In particular the Dalvik VM is not a security boundary, and 59 any app can run native code (see <a href="/sdk/ndk/index.html">the Android 60 NDK</a>). All types of applications — Java, native, and hybrid — 61 are sandboxed in the same way and have the same degree of security from each 62 other.</p> 63 64 65 <a name="signing"></a> 66 <h2>Application Signing</h2> 67 68 <p>All Android applications (.apk files) must be signed with a certificate 69 whose private key is held by their developer. This certificate identifies 70 the author of the application. The certificate does <em>not</em> need to be 71 signed by a certificate authority: it is perfectly allowable, and typical, 72 for Android applications to use self-signed certificates. The purpose of 73 certificates in Android is to distinguish application authors. This allows 74 the system to grant or deny applications access to <a 75 href="/guide/topics/manifest/permission-element.html#plevel">signature-level 76 permissions</a> and to grant or deny an application's <a 77 href="/guide/topics/manifest/manifest-element.html#uid">request to be given 78 the same Linux identity</a> as another application.</p> 79 80 <a name="userid"></a> 81 <h2>User IDs and File Access</h2> 82 83 <p>At install time, Android gives each package a distinct Linux user ID. The 84 identity remains constant for the duration of the package's life on that 85 device. On a different device, the same package may have a different UID; 86 what matters is that each package has a distinct UID on a given device.</p> 87 88 <p>Because security enforcement happens at the 89 process level, the code of any two packages can not normally 90 run in the same process, since they need to run as different Linux users. 91 You can use the {@link android.R.attr#sharedUserId} attribute in the 92 <code>AndroidManifest.xml</code>'s 93 {@link android.R.styleable#AndroidManifest manifest} tag of each package to 94 have them assigned the same user ID. By doing this, for purposes of security 95 the two packages are then treated as being the same application, with the same 96 user ID and file permissions. Note that in order to retain security, only two applications 97 signed with the same signature (and requesting the same sharedUserId) will 98 be given the same user ID.</p> 99 100 <p>Any data stored by an application will be assigned that application's user 101 ID, and not normally accessible to other packages. When creating a new file 102 with {@link android.content.Context#getSharedPreferences}, 103 {@link android.content.Context#openFileOutput}, or 104 {@link android.content.Context#openOrCreateDatabase}, 105 you can use the 106 {@link android.content.Context#MODE_WORLD_READABLE} and/or 107 {@link android.content.Context#MODE_WORLD_WRITEABLE} flags to allow any other 108 package to read/write the file. When setting these flags, the file is still 109 owned by your application, but its global read and/or write permissions have 110 been set appropriately so any other application can see it.</p> 111 112 113 <a name="permissions"></a> 114 <h2>Using Permissions</h2> 115 116 <p>A basic Android application has no permissions associated with it by default, 117 meaning it can not do anything that would adversely impact the user experience 118 or any data on the device. To make use of protected features of the device, 119 you must include in your <code>AndroidManifest.xml</code> one or more 120 <code>{@link android.R.styleable#AndroidManifestUsesPermission <uses-permission>}</code> 121 tags declaring the permissions that your application needs.</p> 122 123 <p>For example, an application that needs to monitor incoming SMS messages would 124 specify:</p> 125 126 <pre><manifest xmlns:android="http://schemas.android.com/apk/res/android"; 127 package="com.android.app.myapp" > 128 <uses-permission android:name="android.permission.RECEIVE_SMS" /> 129 ... 130 </manifest></pre> 131 132 <p>At application install time, permissions requested by the application are 133 granted to it by the package installer, based on checks against the 134 signatures of the applications declaring those permissions and/or interaction 135 with the user. <em>No</em> checks with the user 136 are done while an application is running: it either was granted a particular 137 permission when installed, and can use that feature as desired, or the 138 permission was not granted and any attempt to use the feature will fail 139 without prompting the user.</p> 140 141 <p>Often times a permission failure will result in a {@link 142 java.lang.SecurityException} being thrown back to the application. However, 143 this is not guaranteed to occur everywhere. For example, the {@link 144 android.content.Context#sendBroadcast} method checks permissions as data is 145 being delivered to each receiver, after the method call has returned, so you 146 will not receive an exception if there are permission failures. In almost all 147 cases, however, a permission failure will be printed to the system log.</p> 148 149 <p>The permissions provided by the Android system can be found at {@link 150 android.Manifest.permission}. Any application may also define and enforce its 151 own permissions, so this is not a comprehensive list of all possible 152 permissions.</p> 153 154 <p>A particular permission may be enforced at a number of places during your 155 program's operation:</p> 156 157 <ul> 158 <li>At the time of a call into the system, to prevent an application from 159 executing certain functions.</li> 160 <li>When starting an activity, to prevent applications from launching 161 activities of other applications.</li> 162 <li>Both sending and receiving broadcasts, to control who can receive 163 your broadcast or who can send a broadcast to you.</li> 164 <li>When accessing and operating on a content provider.</li> 165 <li>Binding to or starting a service.</li> 166 </ul> 167 168 169 170 <div class="caution"> 171 <p><strong>Caution:</strong> Over time, 172 new restrictions may be added to the platform such that, in order 173 to use certain APIs, your app must request a permission that it previously did not need. 174 Because existing apps assume access to those APIs is freely available, 175 Android may apply the new permission request to the app's manifest to avoid 176 breaking the app on the new platform version. 177 Android makes the decision as to whether an app might need the permission based on 178 the value provided for the <a 179 href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code targetSdkVersion}</a> 180 attribute. If the value is lower than the version in which the permission was added, then 181 Android adds the permission.</p> 182 <p>For example, the {@link android.Manifest.permission#WRITE_EXTERNAL_STORAGE} permission was 183 added in API level 4 to restrict access to the shared storage space. If your <a 184 href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code targetSdkVersion}</a> 185 is 3 or lower, this permission is added to your app on newer versions of Android.</p> 186 <p>Beware that if this happens to your app, your app listing on Google Play will show these 187 required permissions even though your app might not actually require them.</p> 188 <p>To avoid this and remove the default permissions you don't need, always update your <a 189 href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code targetSdkVersion}</a> 190 to be as high as possible. You can see which permissions were added with each release in the 191 {@link android.os.Build.VERSION_CODES} documentation.</p> 192 </div> 193 194 195 196 <a name="declaring"></a> 197 <h2>Declaring and Enforcing Permissions</h2> 198 199 <p>To enforce your own permissions, you must first declare them in your 200 <code>AndroidManifest.xml</code> using one or more 201 <code>{@link android.R.styleable#AndroidManifestPermission <permission>}</code> 202 tags.</p> 203 204 <p>For example, an application that wants to control who can start one 205 of its activities could declare a permission for this operation as follows:</p> 206 207 <pre><manifest xmlns:android="http://schemas.android.com/apk/res/android"; 208 package="com.me.app.myapp" > 209 <permission android:name="com.me.app.myapp.permission.DEADLY_ACTIVITY" 210 android:label="@string/permlab_deadlyActivity" 211 android:description="@string/permdesc_deadlyActivity" 212 android:permissionGroup="android.permission-group.COST_MONEY" 213 android:protectionLevel="dangerous" /> 214 ... 215 </manifest></pre> 216 217 <p>The {@link android.R.styleable#AndroidManifestPermission_protectionLevel 218 <protectionLevel>} attribute is required, telling the system how the 219 user is to be informed of applications requiring the permission, or who is 220 allowed to hold that permission, as described in the linked documentation.</p> 221 222 <p>The {@link android.R.styleable#AndroidManifestPermission_permissionGroup 223 <permissionGroup>} attribute is optional, and only used to help the system display 224 permissions to the user. You will usually want to set this to either a standard 225 system group (listed in {@link android.Manifest.permission_group 226 android.Manifest.permission_group}) or in more rare cases to one defined by 227 yourself. It is preferred to use an existing group, as this simplifies the 228 permission UI shown to the user.</p> 229 230 <p>Note that both a label and description should be supplied for the 231 permission. These are string resources that can be displayed to the user when 232 they are viewing a list of permissions 233 (<code>{@link android.R.styleable#AndroidManifestPermission_label android:label}</code>) 234 or details on a single permission ( 235 <code>{@link android.R.styleable#AndroidManifestPermission_description android:description}</code>). 236 The label should be short, a few words 237 describing the key piece of functionality the permission is protecting. The 238 description should be a couple sentences describing what the permission allows 239 a holder to do. Our convention for the description is two sentences, the first 240 describing the permission, the second warning the user of what bad things 241 can happen if an application is granted the permission.</p> 242 243 <p>Here is an example of a label and description for the CALL_PHONE 244 permission:</p> 245 246 <pre> 247 <string name="permlab_callPhone">directly call phone numbers</string> 248 <string name="permdesc_callPhone">Allows the application to call 249 phone numbers without your intervention. Malicious applications may 250 cause unexpected calls on your phone bill. Note that this does not 251 allow the application to call emergency numbers.</string> 252 </pre> 253 254 <p>You can look at the permissions currently defined in the system with the 255 Settings app and the shell command <code>adb shell pm list permissions</code>. 256 To use the Settings app, go to Settings > Applications. Pick an app and 257 scroll down to see the permissions that the app uses. For developers, the adb '-s' 258 option displays the permissions in a form similar to how the user will see them:</p> 259 260 <pre> 261 $ adb shell pm list permissions -s 262 All Permissions: 263 264 Network communication: view Wi-Fi state, create Bluetooth connections, full 265 Internet access, view network state 266 267 Your location: access extra location provider commands, fine (GPS) location, 268 mock location sources for testing, coarse (network-based) location 269 270 Services that cost you money: send SMS messages, directly call phone numbers 271 272 ...</pre> 273 274 <a name="manifest"></a> 275 <h3>Enforcing Permissions in AndroidManifest.xml</h3> 276 277 <p>High-level permissions restricting access to entire components of the 278 system or application can be applied through your 279 <code>AndroidManifest.xml</code>. All that this requires is including an {@link 280 android.R.attr#permission android:permission} attribute on the desired 281 component, naming the permission that will be used to control access to 282 it.</p> 283 284 <p><strong>{@link android.app.Activity}</strong> permissions 285 (applied to the 286 {@link android.R.styleable#AndroidManifestActivity <activity>} tag) 287 restrict who can start the associated 288 activity. The permission is checked during 289 {@link android.content.Context#startActivity Context.startActivity()} and 290 {@link android.app.Activity#startActivityForResult Activity.startActivityForResult()}; 291 if the caller does not have 292 the required permission then {@link java.lang.SecurityException} is thrown 293 from the call.</p> 294 295 <p><strong>{@link android.app.Service}</strong> permissions 296 (applied to the 297 {@link android.R.styleable#AndroidManifestService <service>} tag) 298 restrict who can start or bind to the 299 associated service. The permission is checked during 300 {@link android.content.Context#startService Context.startService()}, 301 {@link android.content.Context#stopService Context.stopService()} and 302 {@link android.content.Context#bindService Context.bindService()}; 303 if the caller does not have 304 the required permission then {@link java.lang.SecurityException} is thrown 305 from the call.</p> 306 307 <p><strong>{@link android.content.BroadcastReceiver}</strong> permissions 308 (applied to the 309 {@link android.R.styleable#AndroidManifestReceiver <receiver>} tag) 310 restrict who can send broadcasts to the associated receiver. 311 The permission is checked <em>after</em> 312 {@link android.content.Context#sendBroadcast Context.sendBroadcast()} returns, 313 as the system tries 314 to deliver the submitted broadcast to the given receiver. As a result, a 315 permission failure will not result in an exception being thrown back to the 316 caller; it will just not deliver the intent. In the same way, a permission 317 can be supplied to 318 {@link android.content.Context#registerReceiver(android.content.BroadcastReceiver, android.content.IntentFilter, String, android.os.Handler) 319 Context.registerReceiver()} 320 to control who can broadcast to a programmatically registered receiver. 321 Going the other way, a permission can be supplied when calling 322 {@link android.content.Context#sendBroadcast(Intent, String) Context.sendBroadcast()} 323 to restrict which BroadcastReceiver objects are allowed to receive the broadcast (see 324 below).</p> 325 326 <p><strong>{@link android.content.ContentProvider}</strong> permissions 327 (applied to the 328 {@link android.R.styleable#AndroidManifestProvider <provider>} tag) 329 restrict who can access the data in 330 a {@link android.content.ContentProvider}. (Content providers have an important 331 additional security facility available to them called 332 <a href="#uri">URI permissions</a> which is described later.) 333 Unlike the other components, 334 there are two separate permission attributes you can set: 335 {@link android.R.attr#readPermission android:readPermission} restricts who 336 can read from the provider, and 337 {@link android.R.attr#writePermission android:writePermission} restricts 338 who can write to it. Note that if a provider is protected with both a read 339 and write permission, holding only the write permission does not mean 340 you can read from a provider. The permissions are checked when you first 341 retrieve a provider (if you don't have either permission, a SecurityException 342 will be thrown), and as you perform operations on the provider. Using 343 {@link android.content.ContentResolver#query ContentResolver.query()} requires 344 holding the read permission; using 345 {@link android.content.ContentResolver#insert ContentResolver.insert()}, 346 {@link android.content.ContentResolver#update ContentResolver.update()}, 347 {@link android.content.ContentResolver#delete ContentResolver.delete()} 348 requires the write permission. 349 In all of these cases, not holding the required permission results in a 350 {@link java.lang.SecurityException} being thrown from the call.</p> 351 352 353 <a name="broadcasts"></a> 354 <h3>Enforcing Permissions when Sending Broadcasts</h3> 355 356 <p>In addition to the permission enforcing who can send Intents to a 357 registered {@link android.content.BroadcastReceiver} (as described above), you 358 can also specify a required permission when sending a broadcast. By calling {@link 359 android.content.Context#sendBroadcast(android.content.Intent,String) 360 Context.sendBroadcast()} with a 361 permission string, you require that a receiver's application must hold that 362 permission in order to receive your broadcast.</p> 363 364 <p>Note that both a receiver and a broadcaster can require a permission. When 365 this happens, both permission checks must pass for the Intent to be delivered 366 to the associated target.</p> 367 368 369 <a name="enforcement"></a> 370 <h3>Other Permission Enforcement</h3> 371 372 <p>Arbitrarily fine-grained permissions can be enforced at any call into a 373 service. This is accomplished with the {@link 374 android.content.Context#checkCallingPermission Context.checkCallingPermission()} 375 method. Call with a desired 376 permission string and it will return an integer indicating whether that 377 permission has been granted to the current calling process. Note that this can 378 only be used when you are executing a call coming in from another process, 379 usually through an IDL interface published from a service or in some other way 380 given to another process.</p> 381 382 <p>There are a number of other useful ways to check permissions. If you have 383 the pid of another process, you can use the Context method {@link 384 android.content.Context#checkPermission(String, int, int) Context.checkPermission(String, int, int)} 385 to check a permission against that pid. If you have the package name of another 386 application, you can use the direct PackageManager method {@link 387 android.content.pm.PackageManager#checkPermission(String, String) 388 PackageManager.checkPermission(String, String)} 389 to find out whether that particular package has been granted a specific permission.</p> 390 391 392 <a name="uri"></a> 393 <h2>URI Permissions</h2> 394 395 <p>The standard permission system described so far is often not sufficient 396 when used with content providers. A content provider may want to 397 protect itself with read and write permissions, while its direct clients 398 also need to hand specific URIs to other applications for them to operate on. 399 A typical example is attachments in a mail application. Access to the mail 400 should be protected by permissions, since this is sensitive user data. However, 401 if a URI to an image attachment is given to an image viewer, that image viewer 402 will not have permission to open the attachment since it has no reason to hold 403 a permission to access all e-mail.</p> 404 405 <p>The solution to this problem is per-URI permissions: when starting an 406 activity or returning a result to an activity, the caller can set 407 {@link android.content.Intent#FLAG_GRANT_READ_URI_PERMISSION 408 Intent.FLAG_GRANT_READ_URI_PERMISSION} and/or 409 {@link android.content.Intent#FLAG_GRANT_WRITE_URI_PERMISSION 410 Intent.FLAG_GRANT_WRITE_URI_PERMISSION}. This grants the receiving activity 411 permission access the specific data URI in the Intent, regardless of whether 412 it has any permission to access data in the content provider corresponding 413 to the Intent.</p> 414 415 <p>This mechanism allows a common capability-style model where user interaction 416 (opening an attachment, selecting a contact from a list, etc) drives ad-hoc 417 granting of fine-grained permission. This can be a key facility for reducing 418 the permissions needed by applications to only those directly related to their 419 behavior.</p> 420 421 <p>The granting of fine-grained URI permissions does, however, require some 422 cooperation with the content provider holding those URIs. It is strongly 423 recommended that content providers implement this facility, and declare that 424 they support it through the 425 {@link android.R.styleable#AndroidManifestProvider_grantUriPermissions 426 android:grantUriPermissions} attribute or 427 {@link android.R.styleable#AndroidManifestGrantUriPermission 428 <grant-uri-permissions>} tag.</p> 429 430 <p>More information can be found in the 431 {@link android.content.Context#grantUriPermission Context.grantUriPermission()}, 432 {@link android.content.Context#revokeUriPermission Context.revokeUriPermission()}, and 433 {@link android.content.Context#checkUriPermission Context.checkUriPermission()} 434 methods.</p> 435 436
