sys: don't hold uts_sem while accessing userspace memory

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>

3 files changed, 49 insertions, 44 deletions

diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
index e0903215982d..bbc7cb9faa01 100644
--- a/arch/alpha/kernel/osf_sys.c
+++ b/arch/alpha/kernel/osf_sys.c
@@ -526,24 +526,19 @@ SYSCALL_DEFINE4(osf_mount, unsigned long, typenr, const char __user *, path,
 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)
@@ -563,18 +558,21 @@ SYSCALL_DEFINE2(osf_getdomainname, char __user *, name, int, namelen)
 {
 	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;
 }
 
 /*
@@ -736,13 +734,14 @@ SYSCALL_DEFINE3(osf_sysinfo, int, command, char __user *, buf, long, count)
 	};
 	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);
@@ -750,13 +749,11 @@ SYSCALL_DEFINE3(osf_sysinfo, int, command, char __user *, buf, long, count)
 	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,
diff --git a/arch/sparc/kernel/sys_sparc_32.c b/arch/sparc/kernel/sys_sparc_32.c
index 646988d4c1a3..740f43b9b541 100644
--- 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);
 
-	err = -EFAULT;
-	if (!copy_to_user(name, utsname()->domainname, nlen))
-		err = 0;
+	up_read(&uts_sem);
 
-out:
+	if (copy_to_user(name, tmp, nlen))
+		return -EFAULT;
+	return 0;
+
+out_unlock:
 	up_read(&uts_sem);
 	return err;
 }
diff --git a/arch/sparc/kernel/sys_sparc_64.c b/arch/sparc/kernel/sys_sparc_64.c
index 7f0f7c01b297..f63cd2ea8470 100644
--- 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;
 }