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>

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 300f833..c6921a0 100644 (file)
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -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 @@ fail:
        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,