Mechanism for using chroot on Linux
The new 'chroot' tool at 'os/src/app/chroot' allows for executing subsystems within chroot jails on Linux. For using the tool, please refer to the test case 'os/run/chroot.run'. Fixes #37
This commit is contained in:
Norman Feske
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48d547e2fd
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#
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# \brief Test for using chroot on Linux
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# \author Norman Feske
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# \date 2012-04-18
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#
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#
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if {![have_spec linux]} { puts "Run script requires Linux"; exit 0 }
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#
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# Build
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#
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build { core init app/chroot drivers/timer/linux test/timer }
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if {[catch { exec which setcap }]} {
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puts stderr "Error: setcap not available, please install the libcap2-bin package"
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return 0
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}
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create_boot_directory
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#
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# Generate config
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#
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set config {
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<config>
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<parent-provides>
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<service name="ROM"/>
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<service name="LOG"/>
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<service name="CAP"/>
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<service name="RAM"/>
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<service name="CPU"/>
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<service name="RM"/>
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<service name="PD"/>
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</parent-provides>
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<default-route>
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<any-service> <parent/> <any-child/> </any-service>
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</default-route>
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<start name="timer">
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<resource name="RAM" quantum="1M"/>
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<provides><service name="Timer"/></provides>
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</start>
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<start name="chroot">
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<resource name="RAM" quantum="1G"/>
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<config verbose="yes">
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<root path="chroot_path" />
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<parent-provides>
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<service name="ROM"/>
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<service name="LOG"/>
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<service name="CAP"/>
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<service name="RAM"/>
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<service name="CPU"/>
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<service name="RM"/>
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<service name="PD"/>
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<service name="Timer"/>
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</parent-provides>
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<default-route>
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<any-service> <parent/> </any-service>
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</default-route>
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<start name="test-timer">
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<resource name="RAM" quantum="1G"/>
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</start>
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</config>
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</start>
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</config>
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}
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proc chroot_path { } { return "/tmp/chroot-test" }
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proc chroot_cwd_path { } { return "[chroot_path][pwd]/[run_dir]" }
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proc chroot_genode_tmp_path { } { return "[chroot_path]/tmp/genode-[exec id -u]" }
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proc cleanup_chroot { } {
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catch { exec sudo umount -l [chroot_cwd_path] }
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catch { exec sudo umount -l [chroot_genode_tmp_path] }
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exec rm -rf [chroot_path]
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}
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# replace 'chroot_path' marker in config with actual path
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regsub "chroot_path" $config [chroot_path] config
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install_config $config
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#
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# Copy boot modules into run directory
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#
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# We cannot use the predefined 'build_boot_image' function here because
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# this would create mere symlinks. However, we want to hardlink the
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# run directory into the chroot environment. If the directory entries
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# were symlinks, those would point to nowhere within the chroot.
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#
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foreach binary { core init chroot timer test-timer } {
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exec cp -H bin/$binary [run_dir] }
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#
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# Grant chroot permission to 'chroot' tool
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#
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# CAP_SYS_ADMIN is needed for bind mounting genode runtime directories
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# CAP_SYS_CHROOT is needed to perform the chroot syscall
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#
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exec sudo setcap cap_sys_admin,cap_sys_chroot=ep [run_dir]/chroot
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#
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# Setup chroot environment
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#
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# start with fresh directory
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cleanup_chroot
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exec mkdir -p [chroot_path]
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#
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# Execute test case
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#
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run_genode_until {.*--- timer test finished ---.*} 60
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#
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# Remove artifacts created while running the test
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#
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cleanup_chroot
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# vi: set ft=tcl :
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@ -0,0 +1,211 @@
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/*
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* \brief Utility for using the Linux chroot mechanism with Genode
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* \author Norman Feske
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* \date 2012-04-18
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*/
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/* Genode includes */
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#include <os/config.h>
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#include <base/sleep.h>
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/* Linux includes */
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#include <sys/stat.h>
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#include <sys/mount.h>
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#include <unistd.h>
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#include <errno.h>
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#include <string.h>
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enum { MAX_PATH_LEN = 256 };
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static bool verbose = false;
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/**
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* Return true if specified path is an existing directory
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*/
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static bool is_directory(char const *path)
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{
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struct stat s;
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if (stat(path, &s) != 0)
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return false;
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if (!(s.st_mode & S_IFDIR))
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return false;
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return true;
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}
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static bool is_path_delimiter(char c) { return c == '/'; }
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static bool has_trailing_path_delimiter(char const *path)
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{
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char last_char = 0;
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for (; *path; path++)
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last_char = *path;
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return is_path_delimiter(last_char);
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}
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/**
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* Return number of path elements of given path
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*/
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static size_t num_path_elements(char const *path)
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{
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size_t count = 0;
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/*
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* If path starts with non-slash, the first characters belongs to a path
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* element.
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*/
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if (*path && !is_path_delimiter(*path))
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count = 1;
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/* count slashes */
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for (; *path; path++)
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if (is_path_delimiter(*path))
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count++;
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return count;
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}
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static bool leading_path_elements(char const *path, unsigned num,
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char *dst, size_t dst_len)
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{
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/* counter of path delimiters */
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unsigned count = 0;
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unsigned i = 0;
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if (is_path_delimiter(path[0]))
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num++;
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for (; path[i] && (count < num) && (i < dst_len); i++)
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{
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if (is_path_delimiter(path[i]))
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count++;
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if (count == num)
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break;
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dst[i] = path[i];
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}
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if (i + 1 < dst_len) {
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dst[i] = 0;
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return true;
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}
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/* string is cut, append null termination anyway */
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dst[dst_len - 1] = 0;
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return false;
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}
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static void mirror_path_to_chroot(char const *chroot_path, char const *path)
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{
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char target_path[MAX_PATH_LEN];
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Genode::snprintf(target_path, sizeof(target_path), "%s%s",
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chroot_path, path);
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/*
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* Create directory hierarchy pointing to the target path except for the
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* last element. The last element will be bind-mounted to refer to the
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* original 'path'.
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*/
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for (unsigned i = 1; i <= num_path_elements(target_path); i++)
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{
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char buf[MAX_PATH_LEN];
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leading_path_elements(target_path, i, buf, sizeof(buf));
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/* skip existing directories */
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if (is_directory(buf))
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continue;
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/* create new directory */
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mkdir(buf, 0777);
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}
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umount(target_path);
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if (verbose) {
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PINF("bind mount from: %s", path);
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PINF(" to: %s", target_path);
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}
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if (mount(path, target_path, 0, MS_BIND, 0))
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PERR("bind mount failed (errno=%d: %s)", errno, strerror(errno));
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}
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int main(int, char **argv)
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{
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using namespace Genode;
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static char chroot_path[MAX_PATH_LEN];
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static char cwd_path[MAX_PATH_LEN];
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static char genode_tmp_path[MAX_PATH_LEN];
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/*
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* Read configuration
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*/
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try {
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Xml_node config = Genode::config()->xml_node();
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config.sub_node("root").attribute("path")
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.value(chroot_path, sizeof(chroot_path));
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verbose = config.attribute("verbose").has_value("yes");
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} catch (...) {
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PERR("invalid config");
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return 1;
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}
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getcwd(cwd_path, sizeof(cwd_path));
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uid_t const uid = getuid();
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snprintf(genode_tmp_path, sizeof(genode_tmp_path), "/tmp/genode-%d", uid);
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/*
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* Print diagnostic information
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*/
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if (verbose) {
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PINF("work directory: %s", cwd_path);
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PINF("chroot path: %s", chroot_path);
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PINF("genode tmp path: %s", genode_tmp_path);
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}
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/*
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* Validate chroot path
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*/
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if (!is_directory(chroot_path)) {
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PERR("chroot path does not point to valid directory");
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return 2;
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}
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if (has_trailing_path_delimiter(chroot_path)) {
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PERR("chroot path has trailing slash");
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return 3;
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}
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/*
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* Hardlink directories needed for running Genode within the chroot
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* environment.
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*/
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mirror_path_to_chroot(chroot_path, cwd_path);
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mirror_path_to_chroot(chroot_path, genode_tmp_path);
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printf("changing root to %s ...\n", chroot_path);
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if (chroot(chroot_path)) {
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PERR("chroot failed (errno=%d: %s)", errno, strerror(errno));
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return 4;
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}
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execve("init", argv, environ);
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return 0;
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}
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@ -0,0 +1,19 @@
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TARGET = chroot
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REQUIRES = linux
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SRC_CC = main.cc
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LIBS = cxx env server lx_hybrid
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#
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# XXX find a way to remove superfluous warning:
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#
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# base/include/util/token.h: In constructor ‘Genode::Config::Config()’:
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# base/include/util/token.h:69:67: warning: ‘ret’ may be used uninitialized in
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# this function [-Wuninitialized]
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# base/include/base/capability.h:196:62: note: ‘ret’ was declared here
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# base/include/util/token.h:100:68: warning: ‘prephitmp.1897’ may be used
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# uninitialized in this function
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# [-Wuninitialized]
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# os/include/os/config.h:42:4: note: ‘prephitmp.1897’ was declared here
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#
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CC_WARN = -Wall -Wno-uninitialized
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