diff options
Diffstat (limited to 'bin/named/unix/os.c')
| -rw-r--r-- | bin/named/unix/os.c | 114 |
1 files changed, 91 insertions, 23 deletions
diff --git a/bin/named/unix/os.c b/bin/named/unix/os.c index 05452e3f..6f0a0291 100644 --- a/bin/named/unix/os.c +++ b/bin/named/unix/os.c @@ -17,22 +17,19 @@ #include <config.h> -#include <sys/types.h> #include <sys/stat.h> #include <ctype.h> -#include <stdio.h> -#include <stdlib.h> -#include <string.h> -#include <unistd.h> #include <errno.h> -#include <syslog.h> #include <fcntl.h> +#include <grp.h> /* Required for initgroups() on IRIX. */ #include <pwd.h> -#include <grp.h> +#include <stdio.h> +#include <stdlib.h> +#include <syslog.h> +#include <unistd.h> -#include <isc/result.h> -#include <isc/boolean.h> +#include <isc/string.h> #include <named/main.h> #include <named/os.h> @@ -40,12 +37,25 @@ static char *pidfile = NULL; #ifdef HAVE_LINUXTHREADS static pid_t mainpid = 0; +static isc_boolean_t non_root_caps = ISC_FALSE; #endif #ifdef HAVE_LINUX_CAPABILITY_H -#include <sys/syscall.h> -#include <linux/capability.h> +/* + * We define _LINUX_FS_H to prevent it from being included. We don't need + * anything from it, and the files it includes cause warnings with 2.2 + * kernels, and compilation failures (due to conflicts between <linux/string.h> + * and <string.h>) on 2.3 kernels. + */ +#define _LINUX_FS_H + +#include <sys/syscall.h> /* Required for syscall(). */ +#include <linux/capability.h> /* Required for _LINUX_CAPABILITY_VERSION. */ + +#ifdef HAVE_LINUX_PRCTL_H +#include <sys/prctl.h> /* Required for prctl(). */ +#endif #ifndef SYS_capset #define SYS_capset __NR_capset @@ -56,7 +66,7 @@ linux_setcaps(unsigned int caps) { struct __user_cap_header_struct caphead; struct __user_cap_data_struct cap; - if (getuid() != 0) + if (getuid() != 0 && !non_root_caps) return; memset(&caphead, 0, sizeof caphead); @@ -75,17 +85,41 @@ linux_initialprivs(void) { unsigned int caps; /* - * Drop all privileges except the abilities to bind() to privileged - * ports and chroot(). + * We don't need most privileges, so we drop them right away. + * Later on linux_minprivs() will be called, which will drop our + * capabilities to the minimum needed to run the server. */ caps = 0; + + /* + * We need to be able to bind() to privileged ports, notably port 53! + */ caps |= (1 << CAP_NET_BIND_SERVICE); + + /* + * We need chroot() initially too. + */ caps |= (1 << CAP_SYS_CHROOT); + +#if defined(HAVE_LINUX_PRCTL_H) && defined(PR_SET_KEEPCAPS) + /* + * If the kernel supports keeping capabilities after setuid(), we + * also want the setuid and setgid capabilities. + * + * There's no point turning these on if we don't have PR_SET_KEEPCAPS, + * because changing user ids only works right with linuxthreads if + * we can do it early (before creating threads). + */ + caps |= (1 << CAP_SETGID); + caps |= (1 << CAP_SETUID); +#endif + /* * XXX We might want to add CAP_SYS_RESOURCE, though it's not * clear it would work right given the way linuxthreads work. */ + linux_setcaps(caps); } @@ -94,8 +128,11 @@ linux_minprivs(void) { unsigned int caps; /* - * Drop all privileges except the abilities to bind() to privileged + * Drop all privileges except the ability to bind() to privileged * ports. + * + * It's important that we drop CAP_SYS_CHROOT. If we didn't, it + * chroot() could be used to escape from the chrooted area. */ caps = 0; @@ -104,6 +141,23 @@ linux_minprivs(void) { linux_setcaps(caps); } +#if defined(HAVE_LINUX_PRCTL_H) && defined(PR_SET_KEEPCAPS) +static void +linux_keepcaps(void) { + /* + * Ask the kernel to allow us to keep our capabilities after we + * setuid(). + */ + + if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0) { + if (errno != EINVAL) + ns_main_earlyfatal("prctl() failed: %s", + strerror(errno)); + } else + non_root_caps = ISC_TRUE; +} +#endif + #endif /* HAVE_LINUX_CAPABILITY_H */ @@ -139,7 +193,7 @@ ns_os_daemonize(void) { if (pid == -1) ns_main_earlyfatal("fork(): %s", strerror(errno)); if (pid != 0) - _exit(0); + _exit(0); /* * We're the child. @@ -188,13 +242,6 @@ ns_os_chroot(const char *root) { if (chdir("/") < 0) ns_main_earlyfatal("chdir(/): %s", strerror(errno)); } -#ifdef HAVE_LINUX_CAPABILITY_H - /* - * We must drop the chroot() capability, otherwise it could be used - * to escape. - */ - linux_minprivs(); -#endif } void @@ -204,6 +251,12 @@ ns_os_changeuser(const char *username) { if (username == NULL || getuid() != 0) return; +#ifdef HAVE_LINUXTHREADS + if (!non_root_caps) + ns_main_earlyfatal( + "-u not supported on Linux kernels older than 2.3.99-pre3"); +#endif + if (all_digits(username)) pw = getpwuid((uid_t)atoi(username)); else @@ -219,6 +272,21 @@ ns_os_changeuser(const char *username) { ns_main_earlyfatal("setuid(): %s", strerror(errno)); } +void +ns_os_minprivs(const char *username) { +#ifdef HAVE_LINUX_CAPABILITY_H +#if defined(HAVE_LINUX_PRCTL_H) && defined(PR_SET_KEEPCAPS) + linux_keepcaps(); + ns_os_changeuser(username); +#else + (void)username; +#endif + linux_minprivs(); +#else + (void)username; +#endif /* HAVE_LINUX_CAPABILITY_H */ +} + static int safe_open(const char *filename) { struct stat sb; |