[PATCH] Fix keyctl usage of strnlen_user()

In the small window between strnlen_user() and copy_from_user() userspace
could alter the terminating `\0' character.

Signed-off-by: Davi Arnaut <davi.arnaut@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 10 insertions, 5 deletions

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 90db5c76cf6..0c62798ac7d 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -67,9 +67,10 @@ asmlinkage long sys_add_key(const char __user *_type,
         description = kmalloc(dlen + 1, GFP_KERNEL);
         if (!description)
                 goto error;
+        description[dlen] = '\0';
 
         ret = -EFAULT;
-        if (copy_from_user(description, _description, dlen + 1) != 0)
+        if (copy_from_user(description, _description, dlen) != 0)
                 goto error2;
 
         /* pull the payload in if one was supplied */
@@ -161,9 +162,10 @@ asmlinkage long sys_request_key(const char __user *_type,
         description = kmalloc(dlen + 1, GFP_KERNEL);
         if (!description)
                 goto error;
+        description[dlen] = '\0';
 
         ret = -EFAULT;
-        if (copy_from_user(description, _description, dlen + 1) != 0)
+        if (copy_from_user(description, _description, dlen) != 0)
                 goto error2;
 
         /* pull the callout info into kernel space */
@@ -182,9 +184,10 @@ asmlinkage long sys_request_key(const char __user *_type,
                 callout_info = kmalloc(dlen + 1, GFP_KERNEL);
                 if (!callout_info)
                         goto error2;
+                callout_info[dlen] = '\0';
 
                 ret = -EFAULT;
-                if (copy_from_user(callout_info, _callout_info, dlen + 1) != 0)
+                if (copy_from_user(callout_info, _callout_info, dlen) != 0)
                         goto error3;
         }
 
@@ -279,9 +282,10 @@ long keyctl_join_session_keyring(const char __user *_name)
                 name = kmalloc(nlen + 1, GFP_KERNEL);
                 if (!name)
                         goto error;
+                name[nlen] = '\0';
 
                 ret = -EFAULT;
-                if (copy_from_user(name, _name, nlen + 1) != 0)
+                if (copy_from_user(name, _name, nlen) != 0)
                         goto error2;
         }
 
@@ -583,9 +587,10 @@ long keyctl_keyring_search(key_serial_t ringid,
         description = kmalloc(dlen + 1, GFP_KERNEL);
         if (!description)
                 goto error;
+        description[dlen] = '\0';
 
         ret = -EFAULT;
-        if (copy_from_user(description, _description, dlen + 1) != 0)
+        if (copy_from_user(description, _description, dlen) != 0)
                 goto error2;
 
         /* get the keyring at which to begin the search */