Smack: Implement lock security mode
Linux file locking does not follow the same rules
as other mechanisms. Even though it is a write operation
a process can set a read lock on files which it has open
only for read access. Two programs with read access to
a file can use read locks to communicate.
This is not acceptable in a Mandatory Access Control
environment. Smack treats setting a read lock as the
write operation that it is. Unfortunately, many programs
assume that setting a read lock is a read operation.
These programs are unhappy in the Smack environment.
This patch introduces a new access mode (lock) to address
this problem. A process with lock access to a file can
set a read lock. A process with write access to a file can
set a read lock or a write lock. This prevents a situation
where processes are granted write access just so they can
set read locks.
Targeted for git://git.gitorious.org/smack-next/kernel.git
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 80f4b4a..160aa08e 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -139,7 +139,7 @@
* SMK_LOADLEN: Smack rule length
*/
#define SMK_OACCESS "rwxa"
-#define SMK_ACCESS "rwxat"
+#define SMK_ACCESS "rwxatl"
#define SMK_OACCESSLEN (sizeof(SMK_OACCESS) - 1)
#define SMK_ACCESSLEN (sizeof(SMK_ACCESS) - 1)
#define SMK_OLOADLEN (SMK_LABELLEN + SMK_LABELLEN + SMK_OACCESSLEN)
@@ -282,6 +282,10 @@
case 'T':
perm |= MAY_TRANSMUTE;
break;
+ case 'l':
+ case 'L':
+ perm |= MAY_LOCK;
+ break;
default:
return perm;
}
@@ -452,7 +456,7 @@
/*
* Minor hack for backward compatibility
*/
- if (count != SMK_OLOADLEN && count != SMK_LOADLEN)
+ if (count < SMK_OLOADLEN || count > SMK_LOADLEN)
return -EINVAL;
} else {
if (count >= PAGE_SIZE) {
@@ -592,6 +596,8 @@
seq_putc(s, 'a');
if (srp->smk_access & MAY_TRANSMUTE)
seq_putc(s, 't');
+ if (srp->smk_access & MAY_LOCK)
+ seq_putc(s, 'l');
seq_putc(s, '\n');
}