On Wed, Mar 05, 2008 at 12:51:36AM -0600, Rob Landley wrote: > On Tuesday 04 March 2008 05:22:12 you wrote: > > On Mon, Mar 03, 2008 at 06:28:22PM -0600, Rob Landley wrote: > > > Quick and dirty patch to teach qemu application emulation how to chroot > > > (and drop privs), so you don't have to pollute a target filesystem with > > > host code, and/or figure out how to build qemu static in order to run a > > > dynamic binary. > > > > Hi Rob, > > > > Right, doing the chroot from within qemu avoids the issue with polluting > > the target/. Thanks for the example. > > > > The chroot approach still suffers from the need of initially having higher > > privileges. Personally, I still prefer the sysroot option and avoid that > > need but either way helps me. > > > > Best regards > > Which sysroot option? (I may have missed a patch, I'm a month behind on the > list. This is just something I've meant to submit for... about a year, I > think.) > > You can also teach a bunch of different qemu syscalls (open, unlink, mmap, > exec, fcntl, and 3 dozen others...) to append a prefix to its path, and > perhaps try to prevent them from playing games with symlinks or ".." to break > out of that subdir. But that's a much, much, much more extensive/intrusive > patch.
Hi, This is the updated example from my local git of how it could work, it only maps absolute paths. I don't think taking care of relative paths involves much more code but so far this behaviour has been enough for me. The sim simulators in GDB have a similar --sysroot option which I beleive behaves very similar (or equal). Please note that I'm not trying to jail in a program for security purposes, just for test and debug purposes. My original post can be found here: http://lists.gnu.org/archive/html/qemu-devel/2008-03/msg00027.html Best regards -- Edgar E. Iglesias Axis Communications AB diff --git a/linux-user/main.c b/linux-user/main.c index 0079c7a..8190dbf 100644 --- a/linux-user/main.c +++ b/linux-user/main.c @@ -1904,6 +1904,7 @@ void usage(void) "-h print this help\n" "-g port wait gdb connection to port\n" "-L path set the elf interpreter prefix (default=%s)\n" + "-sysroot Root for system calls with absolute file-names\n" "-s size set the stack size in bytes (default=%ld)\n" "-cpu model select CPU (-cpu ? for list)\n" "-drop-ld-preload drop LD_PRELOAD for target process\n" @@ -1943,6 +1944,7 @@ int main(int argc, char **argv) int gdbstub_port = 0; int drop_ld_preload = 0, environ_count = 0; char **target_environ, **wrk, **dst; + char *sysroot = NULL; if (argc <= 1) usage(); @@ -2014,6 +2016,8 @@ int main(int argc, char **argv) drop_ld_preload = 1; } else if (!strcmp(r, "strace")) { do_strace = 1; + } else if (!strcmp(r, "sysroot")) { + sysroot = argv[optind++]; } else { usage(); @@ -2030,7 +2034,10 @@ int main(int argc, char **argv) memset(info, 0, sizeof(struct image_info)); /* Scan interp_prefix dir for replacement files. */ - init_paths(interp_prefix); + if (sysroot) + init_paths(sysroot, 1); + else + init_paths(interp_prefix, 0); if (cpu_model == NULL) { #if defined(TARGET_I386) diff --git a/linux-user/path.c b/linux-user/path.c index 7da0a8b..5b6abc9 100644 --- a/linux-user/path.c +++ b/linux-user/path.c @@ -25,6 +25,8 @@ struct pathelem }; static struct pathelem *base; +static int use_sysroot; +static size_t sysroot_pathlen; /* First N chars of S1 match S2, and S2 is N chars long. */ static int strneq(const char *s1, unsigned int n, const char *s2) @@ -118,7 +120,7 @@ follow_path(const struct pathelem *cursor, const char *name) return NULL; } -void init_paths(const char *prefix) +void init_paths(const char *prefix, int sysroot) { char pref_buf[PATH_MAX]; @@ -135,15 +137,25 @@ void init_paths(const char *prefix) strcat(pref_buf, prefix); free(cwd); } else - strcpy(pref_buf,prefix + 1); - - base = new_entry("", NULL, pref_buf); - base = add_dir_maybe(base); - if (base->num_entries == 0) { - free (base); - base = NULL; + strcpy(pref_buf, prefix + 1); + + use_sysroot = sysroot; + if (sysroot) { + base = malloc(sizeof (*base)); + sysroot_pathlen = strlen(pref_buf); + base->pathname = malloc(sysroot_pathlen + PATH_MAX + 1); + base->pathname[0] = '/'; + memcpy(base->pathname + 1, pref_buf, sysroot_pathlen); + sysroot_pathlen++; } else { - set_parents(base, base); + base = new_entry("", NULL, pref_buf); + base = add_dir_maybe(base); + if (base->num_entries == 0) { + free (base); + base = NULL; + } else { + set_parents(base, base); + } } } @@ -155,5 +167,12 @@ const char *path(const char *name) if (!base || name[0] != '/') return name; - return follow_path(base, name) ?: name; + if (use_sysroot) { + size_t name_len; + /* Prepend base->pathname to name. */ + name_len = strlen(name); + memcpy (base->pathname + sysroot_pathlen, name, name_len + 1); + return base->pathname; + } else + return follow_path(base, name) ?: name; } diff --git a/linux-user/qemu.h b/linux-user/qemu.h index b33ad89..9e1b4f4 100644 --- a/linux-user/qemu.h +++ b/linux-user/qemu.h @@ -166,7 +166,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1, void gemu_log(const char *fmt, ...) __attribute__((format(printf,1,2))); extern CPUState *global_env; void cpu_loop(CPUState *env); -void init_paths(const char *prefix); +void init_paths(const char *prefix, int sysroot); const char *path(const char *pathname); char *target_strerror(int err);