[PATCH 3.18 19/29] sys: dont hold uts_sem while accessing userspace memory

3.18-stable review patch. If anyone has any objections, please let me know.

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From: Jann Horn jannh@google.com

commit 42a0cc3478584d4d63f68f2f5af021ddbea771fa upstream.

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 jannh@google.com Signed-off-by: Eric W. Biederman ebiederm@xmission.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/alpha/kernel/osf_sys.c | 51 +++++++++----------- arch/sparc/kernel/sys_sparc_32.c | 22 +++++---- arch/sparc/kernel/sys_sparc_64.c | 20 ++++---- kernel/sys.c | 95 ++++++++++++++++++--------------------- kernel/utsname_sysctl.c | 41 ++++++++++------ 5 files changed, 119 insertions(+), 110 deletions(-)

--- a/arch/alpha/kernel/osf_sys.c +++ b/arch/alpha/kernel/osf_sys.c @@ -525,24 +525,19 @@ SYSCALL_DEFINE4(osf_mount, unsigned long SYSCALL_DEFINE1(osf_utsname, char __user *, name) { int error; + char tmp[5 * 32];

down_read(&uts_sem); - error = -EFAULT; - if (copy_to_user(name + 0, utsname()->sysname, 32)) - goto out; - if (copy_to_user(name + 32, utsname()->nodename, 32)) - goto out; - if (copy_to_user(name + 64, utsname()->release, 32)) - goto out; - if (copy_to_user(name + 96, utsname()->version, 32)) - goto out; - if (copy_to_user(name + 128, utsname()->machine, 32)) - goto out; + memcpy(tmp + 0 * 32, utsname()->sysname, 32); + memcpy(tmp + 1 * 32, utsname()->nodename, 32); + memcpy(tmp + 2 * 32, utsname()->release, 32); + memcpy(tmp + 3 * 32, utsname()->version, 32); + memcpy(tmp + 4 * 32, utsname()->machine, 32); + up_read(&uts_sem);

- error = 0; - out: - up_read(&uts_sem); - return error; + if (copy_to_user(name, tmp, sizeof(tmp))) + return -EFAULT; + return 0; }

SYSCALL_DEFINE0(getpagesize) @@ -562,18 +557,21 @@ SYSCALL_DEFINE2(osf_getdomainname, char { int len, err = 0; char *kname; + char tmp[32];

- if (namelen > 32) + if (namelen < 0 || namelen > 32) namelen = 32;

down_read(&uts_sem); kname = utsname()->domainname; len = strnlen(kname, namelen); - if (copy_to_user(name, kname, min(len + 1, namelen))) - err = -EFAULT; + len = min(len + 1, namelen); + memcpy(tmp, kname, len); up_read(&uts_sem);

- return err; + if (copy_to_user(name, tmp, len)) + return -EFAULT; + return 0; }

/* @@ -735,13 +733,14 @@ SYSCALL_DEFINE3(osf_sysinfo, int, comman }; unsigned long offset; const char *res; - long len, err = -EINVAL; + long len; + char tmp[__NEW_UTS_LEN + 1];

offset = command-1; if (offset >= ARRAY_SIZE(sysinfo_table)) { /* Digital UNIX has a few unpublished interfaces here */ printk("sysinfo(%d)", command); - goto out; + return -EINVAL; }

down_read(&uts_sem); @@ -749,13 +748,11 @@ SYSCALL_DEFINE3(osf_sysinfo, int, comman len = strlen(res)+1; if ((unsigned long)len > (unsigned long)count) len = count; - if (copy_to_user(buf, res, len)) - err = -EFAULT; - else - err = 0; + memcpy(tmp, res, len); up_read(&uts_sem); - out: - return err; + if (copy_to_user(buf, tmp, len)) + return -EFAULT; + return 0; }

SYSCALL_DEFINE5(osf_getsysinfo, unsigned long, op, void __user *, buffer, --- a/arch/sparc/kernel/sys_sparc_32.c +++ b/arch/sparc/kernel/sys_sparc_32.c @@ -201,23 +201,27 @@ SYSCALL_DEFINE5(rt_sigaction, int, sig,

asmlinkage long sys_getdomainname(char __user *name, int len) { - int nlen, err; - + int nlen, err; + char tmp[__NEW_UTS_LEN + 1]; + if (len < 0) return -EINVAL;

- down_read(&uts_sem); - + down_read(&uts_sem); + nlen = strlen(utsname()->domainname) + 1; err = -EINVAL; if (nlen > len) - goto out; + goto out_unlock; + memcpy(tmp, utsname()->domainname, nlen); + + up_read(&uts_sem);

- err = -EFAULT; - if (!copy_to_user(name, utsname()->domainname, nlen)) - err = 0; + if (copy_to_user(name, tmp, nlen)) + return -EFAULT; + return 0;

-out: +out_unlock: up_read(&uts_sem); return err; } --- a/arch/sparc/kernel/sys_sparc_64.c +++ b/arch/sparc/kernel/sys_sparc_64.c @@ -524,23 +524,27 @@ extern void check_pending(int signum);

SYSCALL_DEFINE2(getdomainname, char __user *, name, int, len) { - int nlen, err; + int nlen, err; + char tmp[__NEW_UTS_LEN + 1];

if (len < 0) return -EINVAL;

- down_read(&uts_sem); - + down_read(&uts_sem); + nlen = strlen(utsname()->domainname) + 1; err = -EINVAL; if (nlen > len) - goto out; + goto out_unlock; + memcpy(tmp, utsname()->domainname, nlen); + + up_read(&uts_sem);

- err = -EFAULT; - if (!copy_to_user(name, utsname()->domainname, nlen)) - err = 0; + if (copy_to_user(name, tmp, nlen)) + return -EFAULT; + return 0;

-out: +out_unlock: up_read(&uts_sem); return err; } --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1125,18 +1125,19 @@ static int override_release(char __user

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 @@ -1145,55 +1146,46 @@ SYSCALL_DEFINE1(newuname, struct new_uts */ 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

@@ -1207,17 +1199,18 @@ SYSCALL_DEFINE2(sethostname, char __user

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; }

@@ -1225,8 +1218,9 @@ SYSCALL_DEFINE2(sethostname, char __user

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; @@ -1235,11 +1229,11 @@ SYSCALL_DEFINE2(gethostname, char __user 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 @@ -1258,17 +1252,18 @@ SYSCALL_DEFINE2(setdomainname, char __us 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; }

--- a/kernel/utsname_sysctl.c +++ b/kernel/utsname_sysctl.c @@ -17,7 +17,7 @@

#ifdef CONFIG_PROC_SYSCTL

-static void *get_uts(struct ctl_table *table, int write) +static void *get_uts(struct ctl_table *table) { char *which = table->data; struct uts_namespace *uts_ns; @@ -25,21 +25,9 @@ static void *get_uts(struct ctl_table *t uts_ns = current->nsproxy->uts_ns; which = (which - (char *)&init_uts_ns) + (char *)uts_ns;

- if (!write) - down_read(&uts_sem); - else - down_write(&uts_sem); return which; }

-static void put_uts(struct ctl_table *table, int write, void *which) -{ - if (!write) - up_read(&uts_sem); - else - up_write(&uts_sem); -} - /* * Special case of dostring for the UTS structure. This has locks * to observe. Should this be in kernel/sys.c ???? @@ -49,13 +37,34 @@ static int proc_do_uts_string(struct ctl { struct ctl_table uts_table; int r; + char tmp_data[__NEW_UTS_LEN + 1]; + memcpy(&uts_table, table, sizeof(uts_table)); - uts_table.data = get_uts(table, write); + uts_table.data = tmp_data; + + /* + * Buffer the value in tmp_data so that proc_dostring() can be called + * without holding any locks. + * We also need to read the original value in the write==1 case to + * support partial writes. + */ + down_read(&uts_sem); + memcpy(tmp_data, get_uts(table), sizeof(tmp_data)); + up_read(&uts_sem); r = proc_dostring(&uts_table, write, buffer, lenp, ppos); - put_uts(table, write, uts_table.data);

- if (write) + if (write) { + /* + * Write back the new value. + * Note that, since we dropped uts_sem, the result can + * theoretically be incorrect if there are two parallel writes + * at non-zero offsets to the same sysctl. + */ + down_write(&uts_sem); + memcpy(get_uts(table), tmp_data, sizeof(tmp_data)); + up_write(&uts_sem); proc_sys_poll_notify(table->poll); + }

return r; }