CVE-2016-6187 (published 2016-08-06T20:59Z)

The apparmor_setprocattr function in security/apparmor/lsm.c in the Linux kernel before 4.6.5 does not validate the buffer size, which allows local users to gain privileges by triggering an AppArmor setprocattr hook.

Severity: HIGH
CVSS v2 base score: 7.2 (AV:L/AC:L/Au:N/C:C/I:C/A:C)
CVSS v3 base score: 7.8, HIGH (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-264
cwe_name: Permissions, Privileges, and Access Controls
description: Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.
cwe_id: CWE-119
cwe_name: Improper Restriction of Operations within the Bounds of a Memory Buffer
description: The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
extended_description: 
            Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced. This can cause read or write operations to be performed on memory locations that may be associated with other variables, data structures, or internal program data.
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Vegard Nossum
author_date: 2016-07-07 13:41:11-07:00
msg: apparmor: fix oops, validate buffer size in apparmor_setprocattr()

When proc_pid_attr_write() was changed to use memdup_user apparmor's
(interface violating) assumption that the setprocattr buffer was always
a single page was violated.

The size test is not strictly speaking needed as proc_pid_attr_write()
will reject anything larger, but for the sake of robustness we can keep
it in.

SMACK and SELinux look safe to me, but somebody else should probably
have a look just in case.

Based on original patch from Vegard Nossum <vegard.nossum@oracle.com>
modified for the case that apparmor provides null termination.

Fixes: bb646cdb12e75d82258c2f2e7746d5952d3e321a
Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: stable@kernel.org
Signed-off-by: John Johansen <john.johansen@canonical.com>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: lsm.c
change_type: ModificationType.MODIFY
diff: @@ -500,34 +500,34 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
 {
 	struct common_audit_data sa;
 	struct apparmor_audit_data aad = {0,};
-	char *command, *args = value;
+	char *command, *largs = NULL, *args = value;
 	size_t arg_size;
 	int error;
 
 	if (size == 0)
 		return -EINVAL;
-	/* args points to a PAGE_SIZE buffer, AppArmor requires that
-	 * the buffer must be null terminated or have size <= PAGE_SIZE -1
-	 * so that AppArmor can null terminate them
-	 */
-	if (args[size - 1] != '\0') {
-		if (size == PAGE_SIZE)
-			return -EINVAL;
-		args[size] = '\0';
-	}
-
 	/* task can only write its own attributes */
 	if (current != task)
 		return -EACCES;
 
-	args = value;
+	/* AppArmor requires that the buffer must be null terminated atm */
+	if (args[size - 1] != '\0') {
+		/* null terminate */
+		largs = args = kmalloc(size + 1, GFP_KERNEL);
+		if (!args)
+			return -ENOMEM;
+		memcpy(args, value, size);
+		args[size] = '\0';
+	}
+
+	error = -EINVAL;
 	args = strim(args);
 	command = strsep(&args, " ");
 	if (!args)
-		return -EINVAL;
+		goto out;
 	args = skip_spaces(args);
 	if (!*args)
-		return -EINVAL;
+		goto out;
 
 	arg_size = size - (args - (char *) value);
 	if (strcmp(name, "current") == 0) {
@@ -553,10 +553,12 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
 			goto fail;
 	} else
 		/* only support the "current" and "exec" process attributes */
-		return -EINVAL;
+		goto fail;
 
 	if (!error)
 		error = size;
+out:
+	kfree(largs);
 	return error;
 
 fail:
@@ -565,9 +567,9 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
 	aad.profile = aa_current_profile();
 	aad.op = OP_SETPROCATTR;
 	aad.info = name;
-	aad.error = -EINVAL;
+	aad.error = error = -EINVAL;
 	aa_audit_msg(AUDIT_APPARMOR_DENIED, &sa, NULL);
-	return -EINVAL;
+	goto out;
 }
 
 static int apparmor_task_setrlimit(struct task_struct *task,

programming_language: C