CVE-2011-2211: Permissions, Privileges, and Access Controls (CWE-264)
value: The osf_wait4 function in arch/alpha/kernel/osf_sys.c in the Linux kernel before 2.6.39.4 on the Alpha platform uses an incorrect pointer, which allows local users to gain privileges by writing a certain integer value to kernel memory.
CWE description: Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.
Published: 2012-06-13T10:24Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: arch/alpha/kernel/osf_sys.c
Commit date: 2011-06-15 20:04:02 -0700
Commit message: alpha: fix several security issues

Fix several security issues in Alpha-specific syscalls.  Untested, but
mostly trivial.

1. Signedness issue in osf_getdomainname allows copying out-of-bounds
kernel memory to userland.

2. Signedness issue in osf_sysinfo allows copying large amounts of
kernel memory to userland.

3. Typo (?) in osf_getsysinfo bounds minimum instead of maximum copy
size, allowing copying large amounts of kernel memory to userland.

4. Usage of user pointer in osf_wait4 while under KERNEL_DS allows
privilege escalation via writing return value of sys_wait4 to kernel
memory.

Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Diff: diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
index 376f22130791..326f0a2d56e5 100644
--- a/arch/alpha/kernel/osf_sys.c
+++ b/arch/alpha/kernel/osf_sys.c
@@ -407,11 +407,11 @@ SYSCALL_DEFINE2(osf_getdomainname, char __user *, name, int, namelen)
 
 	if (!access_ok(VERIFY_WRITE, name, namelen))
 		return -EFAULT;
 
 	len = namelen;
-	if (namelen > 32)
+	if (len > 32)
 		len = 32;
 
 	down_read(&uts_sem);
 	for (i = 0; i < len; ++i) {
 		__put_user(utsname()->domainname[i], name + i);
@@ -592,11 +592,11 @@ SYSCALL_DEFINE3(osf_sysinfo, int, command, char __user *, buf, long, count)
 	}
 
 	down_read(&uts_sem);
 	res = sysinfo_table[offset];
 	len = strlen(res)+1;
-	if (len > count)
+	if ((unsigned long)len > (unsigned long)count)
 		len = count;
 	if (copy_to_user(buf, res, len))
 		err = -EFAULT;
 	else
 		err = 0;
@@ -647,11 +647,11 @@ SYSCALL_DEFINE5(osf_getsysinfo, unsigned long, op, void __user *, buffer,
 		if (put_user(w, (unsigned long  __user*)buffer))
 			return -EFAULT;
 		return 1;
 
 	case GSI_GET_HWRPB:
-		if (nbytes < sizeof(*hwrpb))
+		if (nbytes > sizeof(*hwrpb))
 			return -EINVAL;
 		if (copy_to_user(buffer, hwrpb, nbytes) != 0)
 			return -EFAULT;
 		return 1;
 
@@ -1006,25 +1006,28 @@ SYSCALL_DEFINE2(osf_getrusage, int, who, struct rusage32 __user *, ru)
 SYSCALL_DEFINE4(osf_wait4, pid_t, pid, int __user *, ustatus, int, options,
 		struct rusage32 __user *, ur)
 {
 	struct rusage r;
 	long ret, err;
+	unsigned int status = 0;
 	mm_segment_t old_fs;
 
 	if (!ur)
 		return sys_wait4(pid, ustatus, options, NULL);
 
 	old_fs = get_fs();
 		
 	set_fs (KERNEL_DS);
-	ret = sys_wait4(pid, ustatus, options, (struct rusage __user *) &r);
+	ret = sys_wait4(pid, (unsigned int __user *) &status, options,
+			(struct rusage __user *) &r);
 	set_fs (old_fs);
 
 	if (!access_ok(VERIFY_WRITE, ur, sizeof(*ur)))
 		return -EFAULT;
 
 	err = 0;
+	err |= put_user(status, ustatus);
 	err |= __put_user(r.ru_utime.tv_sec, &ur->ru_utime.tv_sec);
 	err |= __put_user(r.ru_utime.tv_usec, &ur->ru_utime.tv_usec);
 	err |= __put_user(r.ru_stime.tv_sec, &ur->ru_stime.tv_sec);
 	err |= __put_user(r.ru_stime.tv_usec, &ur->ru_stime.tv_usec);
 	err |= __put_user(r.ru_maxrss, &ur->ru_maxrss);

Vulnerable code: 	if (namelen > 32)
	if (len > count)
		if (nbytes < sizeof(*hwrpb))
	ret = sys_wait4(pid, ustatus, options, (struct rusage __user *) &r);
Fixed code: 	if (len > 32)
	if ((unsigned long)len > (unsigned long)count)
		if (nbytes > sizeof(*hwrpb))
	unsigned int status = 0;
	ret = sys_wait4(pid, (unsigned int __user *) &status, options,
			(struct rusage __user *) &r);
	err |= put_user(status, ustatus);