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Add 'run-as' command implementation as set-uid program.

Typical usage is 'run-as <package-name> <command>' to run <command>
in the data directory, and the user id, of <package-name> if, and only
if <package-name> is the name of an installed and debuggable application.

This relies on the /data/system/packages.list file generated by the
PackageManager service.

BEWARE: This is intended to be available on production devices !
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1 parent 5fc070b commit 1f4d95296acf34a93128332441782a80c10845b4 David 'Digit' Turner committed
Showing with 896 additions and 1 deletion.
  1. +4 −1 include/private/android_filesystem_config.h
  2. +12 −0 run-as/Android.mk
  3. +190 −0 run-as/NOTICE
  4. +471 −0 run-as/package.c
  5. +41 −0 run-as/package.h
  6. +178 −0 run-as/run-as.c
View
5 include/private/android_filesystem_config.h
@@ -169,7 +169,7 @@ static struct fs_path_config android_files[] = {
* Do not change. */
{ 02755, AID_ROOT, AID_NET_RAW, "system/bin/ping" },
{ 02750, AID_ROOT, AID_INET, "system/bin/netcfg" },
- /* the following four files are INTENTIONALLY set-uid, but they
+ /* the following five files are INTENTIONALLY set-uid, but they
* are NOT included on user builds. */
{ 06755, AID_ROOT, AID_ROOT, "system/xbin/su" },
{ 06755, AID_ROOT, AID_ROOT, "system/xbin/librank" },
@@ -177,6 +177,9 @@ static struct fs_path_config android_files[] = {
{ 06755, AID_ROOT, AID_ROOT, "system/xbin/procmem" },
{ 06755, AID_ROOT, AID_ROOT, "system/xbin/tcpdump" },
{ 04770, AID_ROOT, AID_RADIO, "system/bin/pppd-ril" },
+ /* the following file is INTENTIONALLY set-uid, and IS included
+ * in user builds. */
+ { 06750, AID_ROOT, AID_SHELL, "system/bin/run-as" },
{ 00755, AID_ROOT, AID_SHELL, "system/bin/*" },
{ 00755, AID_ROOT, AID_SHELL, "system/xbin/*" },
{ 00750, AID_ROOT, AID_SHELL, "sbin/*" },
View
12 run-as/Android.mk
@@ -0,0 +1,12 @@
+LOCAL_PATH:= $(call my-dir)
+include $(CLEAR_VARS)
+
+LOCAL_SRC_FILES:= run-as.c package.c
+
+LOCAL_MODULE:= run-as
+
+LOCAL_FORCE_STATIC_EXECUTABLE := true
+
+LOCAL_STATIC_LIBRARIES := libc
+
+include $(BUILD_EXECUTABLE)
View
190 run-as/NOTICE
@@ -0,0 +1,190 @@
+
+ Copyright (c) 2005-2008, The Android Open Source Project
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+
+ Apache License
+ Version 2.0, January 2004
+ http://www.apache.org/licenses/
+
+ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+ 1. Definitions.
+
+ "License" shall mean the terms and conditions for use, reproduction,
+ and distribution as defined by Sections 1 through 9 of this document.
+
+ "Licensor" shall mean the copyright owner or entity authorized by
+ the copyright owner that is granting the License.
+
+ "Legal Entity" shall mean the union of the acting entity and all
+ other entities that control, are controlled by, or are under common
+ control with that entity. For the purposes of this definition,
+ "control" means (i) the power, direct or indirect, to cause the
+ direction or management of such entity, whether by contract or
+ otherwise, or (ii) ownership of fifty percent (50%) or more of the
+ outstanding shares, or (iii) beneficial ownership of such entity.
+
+ "You" (or "Your") shall mean an individual or Legal Entity
+ exercising permissions granted by this License.
+
+ "Source" form shall mean the preferred form for making modifications,
+ including but not limited to software source code, documentation
+ source, and configuration files.
+
+ "Object" form shall mean any form resulting from mechanical
+ transformation or translation of a Source form, including but
+ not limited to compiled object code, generated documentation,
+ and conversions to other media types.
+
+ "Work" shall mean the work of authorship, whether in Source or
+ Object form, made available under the License, as indicated by a
+ copyright notice that is included in or attached to the work
+ (an example is provided in the Appendix below).
+
+ "Derivative Works" shall mean any work, whether in Source or Object
+ form, that is based on (or derived from) the Work and for which the
+ editorial revisions, annotations, elaborations, or other modifications
+ represent, as a whole, an original work of authorship. For the purposes
+ of this License, Derivative Works shall not include works that remain
+ separable from, or merely link (or bind by name) to the interfaces of,
+ the Work and Derivative Works thereof.
+
+ "Contribution" shall mean any work of authorship, including
+ the original version of the Work and any modifications or additions
+ to that Work or Derivative Works thereof, that is intentionally
+ submitted to Licensor for inclusion in the Work by the copyright owner
+ or by an individual or Legal Entity authorized to submit on behalf of
+ the copyright owner. For the purposes of this definition, "submitted"
+ means any form of electronic, verbal, or written communication sent
+ to the Licensor or its representatives, including but not limited to
+ communication on electronic mailing lists, source code control systems,
+ and issue tracking systems that are managed by, or on behalf of, the
+ Licensor for the purpose of discussing and improving the Work, but
+ excluding communication that is conspicuously marked or otherwise
+ designated in writing by the copyright owner as "Not a Contribution."
+
+ "Contributor" shall mean Licensor and any individual or Legal Entity
+ on behalf of whom a Contribution has been received by Licensor and
+ subsequently incorporated within the Work.
+
+ 2. Grant of Copyright License. Subject to the terms and conditions of
+ this License, each Contributor hereby grants to You a perpetual,
+ worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+ copyright license to reproduce, prepare Derivative Works of,
+ publicly display, publicly perform, sublicense, and distribute the
+ Work and such Derivative Works in Source or Object form.
+
+ 3. Grant of Patent License. Subject to the terms and conditions of
+ this License, each Contributor hereby grants to You a perpetual,
+ worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+ (except as stated in this section) patent license to make, have made,
+ use, offer to sell, sell, import, and otherwise transfer the Work,
+ where such license applies only to those patent claims licensable
+ by such Contributor that are necessarily infringed by their
+ Contribution(s) alone or by combination of their Contribution(s)
+ with the Work to which such Contribution(s) was submitted. If You
+ institute patent litigation against any entity (including a
+ cross-claim or counterclaim in a lawsuit) alleging that the Work
+ or a Contribution incorporated within the Work constitutes direct
+ or contributory patent infringement, then any patent licenses
+ granted to You under this License for that Work shall terminate
+ as of the date such litigation is filed.
+
+ 4. Redistribution. You may reproduce and distribute copies of the
+ Work or Derivative Works thereof in any medium, with or without
+ modifications, and in Source or Object form, provided that You
+ meet the following conditions:
+
+ (a) You must give any other recipients of the Work or
+ Derivative Works a copy of this License; and
+
+ (b) You must cause any modified files to carry prominent notices
+ stating that You changed the files; and
+
+ (c) You must retain, in the Source form of any Derivative Works
+ that You distribute, all copyright, patent, trademark, and
+ attribution notices from the Source form of the Work,
+ excluding those notices that do not pertain to any part of
+ the Derivative Works; and
+
+ (d) If the Work includes a "NOTICE" text file as part of its
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+ of the NOTICE file are for informational purposes only and
+ do not modify the License. You may add Your own attribution
+ notices within Derivative Works that You distribute, alongside
+ or as an addendum to the NOTICE text from the Work, provided
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+ as modifying the License.
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+ You may add Your own copyright statement to Your modifications and
+ may provide additional or different license terms and conditions
+ for use, reproduction, or distribution of Your modifications, or
+ for any such Derivative Works as a whole, provided Your use,
+ reproduction, and distribution of the Work otherwise complies with
+ the conditions stated in this License.
+
+ 5. Submission of Contributions. Unless You explicitly state otherwise,
+ any Contribution intentionally submitted for inclusion in the Work
+ by You to the Licensor shall be under the terms and conditions of
+ this License, without any additional terms or conditions.
+ Notwithstanding the above, nothing herein shall supersede or modify
+ the terms of any separate license agreement you may have executed
+ with Licensor regarding such Contributions.
+
+ 6. Trademarks. This License does not grant permission to use the trade
+ names, trademarks, service marks, or product names of the Licensor,
+ except as required for reasonable and customary use in describing the
+ origin of the Work and reproducing the content of the NOTICE file.
+
+ 7. Disclaimer of Warranty. Unless required by applicable law or
+ agreed to in writing, Licensor provides the Work (and each
+ Contributor provides its Contributions) on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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+ of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+ PARTICULAR PURPOSE. You are solely responsible for determining the
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+ risks associated with Your exercise of permissions under this License.
+
+ 8. Limitation of Liability. In no event and under no legal theory,
+ whether in tort (including negligence), contract, or otherwise,
+ unless required by applicable law (such as deliberate and grossly
+ negligent acts) or agreed to in writing, shall any Contributor be
+ liable to You for damages, including any direct, indirect, special,
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+
+ END OF TERMS AND CONDITIONS
+
View
471 run-as/package.c
@@ -0,0 +1,471 @@
+/*
+**
+** Copyright 2010, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License");
+** you may not use this file except in compliance with the License.
+** You may obtain a copy of the License at
+**
+** http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing, software
+** distributed under the License is distributed on an "AS IS" BASIS,
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+** See the License for the specific language governing permissions and
+** limitations under the License.
+*/
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <private/android_filesystem_config.h>
+#include "package.h"
+
+/*
+ * WARNING WARNING WARNING WARNING
+ *
+ * The following code runs as root on production devices, before
+ * the run-as command has dropped the uid/gid. Hence be very
+ * conservative and keep in mind the following:
+ *
+ * - Performance does not matter here, clarity and safety of the code
+ * does however. Documentation is a must.
+ *
+ * - Avoid calling C library functions with complex implementations
+ * like malloc() and printf(). You want to depend on simple system
+ * calls instead, which behaviour is not going to be altered in
+ * unpredictible ways by environment variables or system properties.
+ *
+ * - Do not trust user input and/or the filesystem whenever possible.
+ *
+ */
+
+/* The file containing the list of installed packages on the system */
+#define PACKAGES_LIST_FILE "/data/system/packages.list"
+
+/* This should be large enough to hold the content of the package database file */
+#define PACKAGES_LIST_BUFFER_SIZE 8192
+
+/* Copy 'srclen' string bytes from 'src' into buffer 'dst' of size 'dstlen'
+ * This function always zero-terminate the destination buffer unless
+ * 'dstlen' is 0, even in case of overflow.
+ */
+static void
+string_copy(char* dst, size_t dstlen, const char* src, size_t srclen)
+{
+ const char* srcend = src + srclen;
+ const char* dstend = dst + dstlen;
+
+ if (dstlen == 0)
+ return;
+
+ dstend--; /* make room for terminating zero */
+
+ while (dst < dstend && src < srcend && *src != '\0')
+ *dst++ = *src++;
+
+ *dst = '\0'; /* zero-terminate result */
+}
+
+/* Read up to 'buffsize' bytes into 'buff' from the file
+ * named 'filename'. Return byte length on success, or -1
+ * on error.
+ */
+static int
+read_file(const char* filename, char* buff, size_t buffsize)
+{
+ int fd, len, old_errno;
+
+ /* check the input buffer size */
+ if (buffsize >= INT_MAX) {
+ errno = EINVAL;
+ return -1;
+ }
+
+ /* open the file for reading */
+ do {
+ fd = open(filename, O_RDONLY);
+ } while (fd < 0 && errno == EINTR);
+
+ if (fd < 0)
+ return -1;
+
+ /* read the content */
+ do {
+ len = read(fd, buff, buffsize);
+ } while (len < 0 && errno == EINTR);
+
+ /* close the file, preserve old errno for better diagnostics */
+ old_errno = errno;
+ close(fd);
+ errno = old_errno;
+
+ return len;
+}
+
+/* Check that a given directory:
+ * - exists
+ * - is owned by a given uid/gid
+ * - is a real directory, not a symlink
+ * - isn't readable or writable by others
+ *
+ * Return 0 on success, or -1 on error.
+ * errno is set to EINVAL in case of failed check.
+ */
+static int
+check_directory_ownership(const char* path, uid_t uid)
+{
+ int ret;
+ struct stat st;
+
+ do {
+ ret = lstat(path, &st);
+ } while (ret < 0 && errno == EINTR);
+
+ if (ret < 0)
+ return -1;
+
+ /* must be a real directory, not a symlink */
+ if (!S_ISDIR(st.st_mode))
+ goto BAD;
+
+ /* must be owned by specific uid/gid */
+ if (st.st_uid != uid || st.st_gid != uid)
+ goto BAD;
+
+ /* must not be readable or writable by others */
+ if ((st.st_mode & (S_IROTH|S_IWOTH)) != 0)
+ goto BAD;
+
+ /* everything ok */
+ return 0;
+
+BAD:
+ errno = EINVAL;
+ return -1;
+}
+
+/* This function is used to check the data directory path for safety.
+ * We check that every sub-directory is owned by the 'system' user
+ * and exists and is not a symlink. We also check that the full directory
+ * path is properly owned by the user ID.
+ *
+ * Return 0 on success, -1 on error.
+ */
+int
+check_data_path(const char* dataPath, uid_t uid)
+{
+ int nn;
+
+ /* the path should be absolute */
+ if (dataPath[0] != '/') {
+ errno = EINVAL;
+ return -1;
+ }
+
+ /* look for all sub-paths, we do that by finding
+ * directory separators in the input path and
+ * checking each sub-path independently
+ */
+ for (nn = 1; dataPath[nn] != '\0'; nn++)
+ {
+ char subpath[PATH_MAX];
+
+ /* skip non-separator characters */
+ if (dataPath[nn] != '/')
+ continue;
+
+ /* handle trailing separator case */
+ if (dataPath[nn+1] == '\0') {
+ break;
+ }
+
+ /* found a separator, check that dataPath is not too long. */
+ if (nn >= (int)(sizeof subpath)) {
+ errno = EINVAL;
+ return -1;
+ }
+
+ /* reject any '..' subpath */
+ if (nn >= 3 &&
+ dataPath[nn-3] == '/' &&
+ dataPath[nn-2] == '.' &&
+ dataPath[nn-1] == '.') {
+ errno = EINVAL;
+ return -1;
+ }
+
+ /* copy to 'subpath', then check ownership */
+ memcpy(subpath, dataPath, nn);
+ subpath[nn] = '\0';
+
+ if (check_directory_ownership(subpath, AID_SYSTEM) < 0)
+ return -1;
+ }
+
+ /* All sub-paths were checked, now verify that the full data
+ * directory is owned by the application uid
+ */
+ if (check_directory_ownership(dataPath, uid) < 0)
+ return -1;
+
+ /* all clear */
+ return 0;
+}
+
+/* Return TRUE iff a character is a space or tab */
+static inline int
+is_space(char c)
+{
+ return (c == ' ' || c == '\t');
+}
+
+/* Skip any space or tab character from 'p' until 'end' is reached.
+ * Return new position.
+ */
+static const char*
+skip_spaces(const char* p, const char* end)
+{
+ while (p < end && is_space(*p))
+ p++;
+
+ return p;
+}
+
+/* Skip any non-space and non-tab character from 'p' until 'end'.
+ * Return new position.
+ */
+static const char*
+skip_non_spaces(const char* p, const char* end)
+{
+ while (p < end && !is_space(*p))
+ p++;
+
+ return p;
+}
+
+/* Find the first occurence of 'ch' between 'p' and 'end'
+ * Return its position, or 'end' if none is found.
+ */
+static const char*
+find_first(const char* p, const char* end, char ch)
+{
+ while (p < end && *p != ch)
+ p++;
+
+ return p;
+}
+
+/* Check that the non-space string starting at 'p' and eventually
+ * ending at 'end' equals 'name'. Return new position (after name)
+ * on success, or NULL on failure.
+ *
+ * This function fails is 'name' is NULL, empty or contains any space.
+ */
+static const char*
+compare_name(const char* p, const char* end, const char* name)
+{
+ /* 'name' must not be NULL or empty */
+ if (name == NULL || name[0] == '\0' || p == end)
+ return NULL;
+
+ /* compare characters to those in 'name', excluding spaces */
+ while (*name) {
+ /* note, we don't check for *p == '\0' since
+ * it will be caught in the next conditional.
+ */
+ if (p >= end || is_space(*p))
+ goto BAD;
+
+ if (*p != *name)
+ goto BAD;
+
+ p++;
+ name++;
+ }
+
+ /* must be followed by end of line or space */
+ if (p < end && !is_space(*p))
+ goto BAD;
+
+ return p;
+
+BAD:
+ return NULL;
+}
+
+/* Parse one or more whitespace characters starting from '*pp'
+ * until 'end' is reached. Updates '*pp' on exit.
+ *
+ * Return 0 on success, -1 on failure.
+ */
+static int
+parse_spaces(const char** pp, const char* end)
+{
+ const char* p = *pp;
+
+ if (p >= end || !is_space(*p)) {
+ errno = EINVAL;
+ return -1;
+ }
+ p = skip_spaces(p, end);
+ *pp = p;
+ return 0;
+}
+
+/* Parse a positive decimal number starting from '*pp' until 'end'
+ * is reached. Adjust '*pp' on exit. Return decimal value or -1
+ * in case of error.
+ *
+ * If the value is larger than INT_MAX, -1 will be returned,
+ * and errno set to EOVERFLOW.
+ *
+ * If '*pp' does not start with a decimal digit, -1 is returned
+ * and errno set to EINVAL.
+ */
+static int
+parse_positive_decimal(const char** pp, const char* end)
+{
+ const char* p = *pp;
+ int value = 0;
+ int overflow = 0;
+
+ if (p >= end || *p < '0' || *p > '9') {
+ errno = EINVAL;
+ return -1;
+ }
+
+ while (p < end) {
+ int ch = *p;
+ unsigned d = (unsigned)(ch - '0');
+ int val2;
+
+ if (d >= 10U) /* d is unsigned, no lower bound check */
+ break;
+
+ val2 = value*10 + (int)d;
+ if (val2 < value)
+ overflow = 1;
+ value = val2;
+ p++;
+ }
+ *pp = p;
+
+ if (overflow) {
+ errno = EOVERFLOW;
+ value = -1;
+ }
+ return value;
+
+BAD:
+ *pp = p;
+ return -1;
+}
+
+/* Read the system's package database and extract information about
+ * 'pkgname'. Return 0 in case of success, or -1 in case of error.
+ *
+ * If the package is unknown, return -1 and set errno to ENOENT
+ * If the package database is corrupted, return -1 and set errno to EINVAL
+ */
+int
+get_package_info(const char* pkgName, PackageInfo *info)
+{
+ static char buffer[PACKAGES_LIST_BUFFER_SIZE];
+ int buffer_len;
+ const char* p;
+ const char* buffer_end;
+ int result;
+
+ info->uid = 0;
+ info->isDebuggable = 0;
+ info->dataDir[0] = '\0';
+
+ buffer_len = read_file(PACKAGES_LIST_FILE, buffer, sizeof buffer);
+ if (buffer_len < 0)
+ return -1;
+
+ p = buffer;
+ buffer_end = buffer + buffer_len;
+
+ /* expect the following format on each line of the control file:
+ *
+ * <pkgName> <uid> <debugFlag> <dataDir>
+ *
+ * where:
+ * <pkgName> is the package's name
+ * <uid> is the application-specific user Id (decimal)
+ * <debugFlag> is 1 if the package is debuggable, or 0 otherwise
+ * <dataDir> is the path to the package's data directory (e.g. /data/data/com.example.foo)
+ *
+ * The file is generated in com.android.server.PackageManagerService.Settings.writeLP()
+ */
+
+ while (p < buffer_end) {
+ /* find end of current line and start of next one */
+ const char* end = find_first(p, buffer_end, '\n');
+ const char* next = (end < buffer_end) ? end + 1 : buffer_end;
+ const char* q;
+ int uid, debugFlag;
+
+ /* first field is the package name */
+ p = compare_name(p, end, pkgName);
+ if (p == NULL)
+ goto NEXT_LINE;
+
+ /* skip spaces */
+ if (parse_spaces(&p, end) < 0)
+ goto BAD_FORMAT;
+
+ /* second field is the pid */
+ uid = parse_positive_decimal(&p, end);
+ if (uid < 0)
+ return -1;
+
+ info->uid = (uid_t) uid;
+
+ /* skip spaces */
+ if (parse_spaces(&p, end) < 0)
+ goto BAD_FORMAT;
+
+ /* third field is debug flag (0 or 1) */
+ debugFlag = parse_positive_decimal(&p, end);
+ switch (debugFlag) {
+ case 0:
+ info->isDebuggable = 0;
+ break;
+ case 1:
+ info->isDebuggable = 1;
+ break;
+ default:
+ goto BAD_FORMAT;
+ }
+
+ /* skip spaces */
+ if (parse_spaces(&p, end) < 0)
+ goto BAD_FORMAT;
+
+ /* fourth field is data directory path and must not contain
+ * spaces.
+ */
+ q = skip_non_spaces(p, end);
+ if (q == p)
+ goto BAD_FORMAT;
+
+ string_copy(info->dataDir, sizeof info->dataDir, p, q - p);
+
+ /* Ignore the rest */
+ return 0;
+
+ NEXT_LINE:
+ p = next;
+ }
+
+ /* the package is unknown */
+ errno = ENOENT;
+ return -1;
+
+BAD_FORMAT:
+ errno = EINVAL;
+ return -1;
+}
View
41 run-as/package.h
@@ -0,0 +1,41 @@
+/*
+**
+** Copyright 2010, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License");
+** you may not use this file except in compliance with the License.
+** You may obtain a copy of the License at
+**
+** http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing, software
+** distributed under the License is distributed on an "AS IS" BASIS,
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+** See the License for the specific language governing permissions and
+** limitations under the License.
+*/
+#ifndef RUN_AS_PACKAGE_H
+#define RUN_AS_PACKAGE_H
+
+#include <limits.h>
+#include <sys/types.h>
+
+typedef enum {
+ PACKAGE_IS_DEBUGGABLE = 0,
+ PACKAGE_IS_NOT_DEBUGGABLE,
+ PACKAGE_IS_UNKNOWN,
+} PackageStatus;
+
+typedef struct {
+ uid_t uid;
+ char isDebuggable;
+ char dataDir[PATH_MAX];
+} PackageInfo;
+
+/* see documentation in package.c for these functiosn */
+
+extern int get_package_info(const char* packageName, PackageInfo* info);
+
+extern int check_data_path(const char* dataDir, uid_t uid);
+
+#endif /* RUN_AS_PACKAGE_H */
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178 run-as/run-as.c
@@ -0,0 +1,178 @@
+/*
+**
+** Copyright 2010, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License");
+** you may not use this file except in compliance with the License.
+** You may obtain a copy of the License at
+**
+** http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing, software
+** distributed under the License is distributed on an "AS IS" BASIS,
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+** See the License for the specific language governing permissions and
+** limitations under the License.
+*/
+
+#define PROGNAME "run-as"
+#define LOG_TAG PROGNAME
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <errno.h>
+#include <unistd.h>
+#include <time.h>
+#include <stdarg.h>
+
+#include <private/android_filesystem_config.h>
+#include "package.h"
+
+/*
+ * WARNING WARNING WARNING WARNING
+ *
+ * This program runs as set-uid root on Android production devices.
+ * Be very conservative when modifying it to avoid any serious
+ * security issue. Keep in mind the following:
+ *
+ * - This program should only run for the 'root' or 'shell' users
+ *
+ * - Statically link against the C library, and avoid anything that
+ * is more complex than simple system calls until the uid/gid has
+ * been dropped to that of a normal user or you are sure to exit.
+ *
+ * This avoids depending on environment variables, system properties
+ * and other external factors that may affect the C library in
+ * unpredictable ways.
+ *
+ * - Do not trust user input and/or the filesystem whenever possible.
+ *
+ * Read README.TXT for more details.
+ *
+ *
+ *
+ * The purpose of this program is to run a command as a specific
+ * application user-id. Typical usage is:
+ *
+ * run-as <package-name> <command> <args>
+ *
+ * The 'run-as' binary is setuid, but will check the following:
+ *
+ * - that it is invoked from the 'shell' or 'root' user (abort otherwise)
+ * - that '<package-name>' is the name of an installed and debuggable package
+ * - that the package's data directory is well-formed (see package.c)
+ *
+ * If so, it will cd to the package's data directory, drop to the application's
+ * user id / group id then run the command there.
+ *
+ * This can be useful for a number of different things on production devices:
+ *
+ * - Allow application developers to look at their own applicative data
+ * during development.
+ *
+ * - Run the 'gdbserver' binary executable to allow native debugging
+ */
+
+static void
+usage(void)
+{
+ const char* str = "Usage: " PROGNAME " <package-name> <command> [<args>]\n\n";
+ write(1, str, strlen(str));
+ exit(1);
+}
+
+
+static void
+panic(const char* format, ...)
+{
+ va_list args;
+
+ fprintf(stderr, "%s: ", PROGNAME);
+ va_start(args, format);
+ vfprintf(stderr, format, args);
+ va_end(args);
+ exit(1);
+}
+
+
+int main(int argc, char **argv)
+{
+ const char* pkgname;
+ int myuid, uid, gid;
+ PackageInfo info;
+
+ /* check arguments */
+ if (argc < 2)
+ usage();
+
+ /* check userid of caller - must be 'shell' or 'root' */
+ myuid = getuid();
+ if (myuid != AID_SHELL && myuid != AID_ROOT) {
+ panic("only 'shell' or 'root' users can run this program\n");
+ }
+
+ /* retrieve package information from system */
+ pkgname = argv[1];
+ if (get_package_info(pkgname, &info) < 0) {
+ panic("Package '%s' is unknown\n", pkgname);
+ return 1;
+ }
+
+ /* reject system packages */
+ if (info.uid < AID_APP) {
+ panic("Package '%s' is not an application\n", pkgname);
+ return 1;
+ }
+
+ /* reject any non-debuggable package */
+ if (!info.isDebuggable) {
+ panic("Package '%s' is not debuggable\n", pkgname);
+ return 1;
+ }
+
+ /* check that the data directory path is valid */
+ if (check_data_path(info.dataDir, info.uid) < 0) {
+ panic("Package '%s' has corrupt installation\n", pkgname);
+ return 1;
+ }
+
+ /* then move to it */
+ {
+ int ret;
+ do {
+ ret = chdir(info.dataDir);
+ } while (ret < 0 && errno == EINTR);
+
+ if (ret < 0) {
+ panic("Could not cd to package's data directory: %s\n", strerror(errno));
+ return 1;
+ }
+ }
+
+ /* Ensure that we change all real/effective/saved IDs at the
+ * same time to avoid nasty surprises.
+ */
+ uid = gid = info.uid;
+ if(setresgid(gid,gid,gid) || setresuid(uid,uid,uid)) {
+ panic("Permission denied\n");
+ return 1;
+ }
+
+ /* User specified command for exec. */
+ if (argc >= 3 ) {
+ if (execvp(argv[2], argv+2) < 0) {
+ panic("exec failed for %s Error:%s\n", argv[2], strerror(errno));
+ return -errno;
+ }
+ }
+
+ /* Default exec shell. */
+ execlp("/system/bin/sh", "sh", NULL);
+
+ panic("exec failed\n");
+ return 1;
+}

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