From 42a0cc3478584d4d63f68f2f5af021ddbea771fa Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Mon, 25 Jun 2018 18:34:10 +0200 Subject: sys: don't hold uts_sem while accessing userspace memory Holding uts_sem as a writer while accessing userspace memory allows a namespace admin to stall all processes that attempt to take uts_sem. Instead, move data through stack buffers and don't access userspace memory while uts_sem is held. Cc: stable@vger.kernel.org Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Jann Horn Signed-off-by: Eric W. Biederman --- kernel/sys.c | 95 ++++++++++++++++++++++++++++-------------------------------- 1 file changed, 45 insertions(+), 50 deletions(-) (limited to 'kernel/sys.c') diff --git a/kernel/sys.c b/kernel/sys.c index 38509dc1f77b..69b9a37ecf0d 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1237,18 +1237,19 @@ static int override_release(char __user *release, size_t len) SYSCALL_DEFINE1(newuname, struct new_utsname __user *, name) { - int errno = 0; + struct new_utsname tmp; down_read(&uts_sem); - if (copy_to_user(name, utsname(), sizeof *name)) - errno = -EFAULT; + memcpy(&tmp, utsname(), sizeof(tmp)); up_read(&uts_sem); + if (copy_to_user(name, &tmp, sizeof(tmp))) + return -EFAULT; - if (!errno && override_release(name->release, sizeof(name->release))) - errno = -EFAULT; - if (!errno && override_architecture(name)) - errno = -EFAULT; - return errno; + if (override_release(name->release, sizeof(name->release))) + return -EFAULT; + if (override_architecture(name)) + return -EFAULT; + return 0; } #ifdef __ARCH_WANT_SYS_OLD_UNAME @@ -1257,55 +1258,46 @@ SYSCALL_DEFINE1(newuname, struct new_utsname __user *, name) */ SYSCALL_DEFINE1(uname, struct old_utsname __user *, name) { - int error = 0; + struct old_utsname tmp; if (!name) return -EFAULT; down_read(&uts_sem); - if (copy_to_user(name, utsname(), sizeof(*name))) - error = -EFAULT; + memcpy(&tmp, utsname(), sizeof(tmp)); up_read(&uts_sem); + if (copy_to_user(name, &tmp, sizeof(tmp))) + return -EFAULT; - if (!error && override_release(name->release, sizeof(name->release))) - error = -EFAULT; - if (!error && override_architecture(name)) - error = -EFAULT; - return error; + if (override_release(name->release, sizeof(name->release))) + return -EFAULT; + if (override_architecture(name)) + return -EFAULT; + return 0; } SYSCALL_DEFINE1(olduname, struct oldold_utsname __user *, name) { - int error; + struct oldold_utsname tmp = {}; if (!name) return -EFAULT; - if (!access_ok(VERIFY_WRITE, name, sizeof(struct oldold_utsname))) - return -EFAULT; down_read(&uts_sem); - error = __copy_to_user(&name->sysname, &utsname()->sysname, - __OLD_UTS_LEN); - error |= __put_user(0, name->sysname + __OLD_UTS_LEN); - error |= __copy_to_user(&name->nodename, &utsname()->nodename, - __OLD_UTS_LEN); - error |= __put_user(0, name->nodename + __OLD_UTS_LEN); - error |= __copy_to_user(&name->release, &utsname()->release, - __OLD_UTS_LEN); - error |= __put_user(0, name->release + __OLD_UTS_LEN); - error |= __copy_to_user(&name->version, &utsname()->version, - __OLD_UTS_LEN); - error |= __put_user(0, name->version + __OLD_UTS_LEN); - error |= __copy_to_user(&name->machine, &utsname()->machine, - __OLD_UTS_LEN); - error |= __put_user(0, name->machine + __OLD_UTS_LEN); + memcpy(&tmp.sysname, &utsname()->sysname, __OLD_UTS_LEN); + memcpy(&tmp.nodename, &utsname()->nodename, __OLD_UTS_LEN); + memcpy(&tmp.release, &utsname()->release, __OLD_UTS_LEN); + memcpy(&tmp.version, &utsname()->version, __OLD_UTS_LEN); + memcpy(&tmp.machine, &utsname()->machine, __OLD_UTS_LEN); up_read(&uts_sem); + if (copy_to_user(name, &tmp, sizeof(tmp))) + return -EFAULT; - if (!error && override_architecture(name)) - error = -EFAULT; - if (!error && override_release(name->release, sizeof(name->release))) - error = -EFAULT; - return error ? -EFAULT : 0; + if (override_architecture(name)) + return -EFAULT; + if (override_release(name->release, sizeof(name->release))) + return -EFAULT; + return 0; } #endif @@ -1319,17 +1311,18 @@ SYSCALL_DEFINE2(sethostname, char __user *, name, int, len) if (len < 0 || len > __NEW_UTS_LEN) return -EINVAL; - down_write(&uts_sem); errno = -EFAULT; if (!copy_from_user(tmp, name, len)) { - struct new_utsname *u = utsname(); + struct new_utsname *u; + down_write(&uts_sem); + u = utsname(); memcpy(u->nodename, tmp, len); memset(u->nodename + len, 0, sizeof(u->nodename) - len); errno = 0; uts_proc_notify(UTS_PROC_HOSTNAME); + up_write(&uts_sem); } - up_write(&uts_sem); return errno; } @@ -1337,8 +1330,9 @@ SYSCALL_DEFINE2(sethostname, char __user *, name, int, len) SYSCALL_DEFINE2(gethostname, char __user *, name, int, len) { - int i, errno; + int i; struct new_utsname *u; + char tmp[__NEW_UTS_LEN + 1]; if (len < 0) return -EINVAL; @@ -1347,11 +1341,11 @@ SYSCALL_DEFINE2(gethostname, char __user *, name, int, len) i = 1 + strlen(u->nodename); if (i > len) i = len; - errno = 0; - if (copy_to_user(name, u->nodename, i)) - errno = -EFAULT; + memcpy(tmp, u->nodename, i); up_read(&uts_sem); - return errno; + if (copy_to_user(name, tmp, i)) + return -EFAULT; + return 0; } #endif @@ -1370,17 +1364,18 @@ SYSCALL_DEFINE2(setdomainname, char __user *, name, int, len) if (len < 0 || len > __NEW_UTS_LEN) return -EINVAL; - down_write(&uts_sem); errno = -EFAULT; if (!copy_from_user(tmp, name, len)) { - struct new_utsname *u = utsname(); + struct new_utsname *u; + down_write(&uts_sem); + u = utsname(); memcpy(u->domainname, tmp, len); memset(u->domainname + len, 0, sizeof(u->domainname) - len); errno = 0; uts_proc_notify(UTS_PROC_DOMAINNAME); + up_write(&uts_sem); } - up_write(&uts_sem); return errno; } -- cgit