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Subject[PATCH] Smackv10: Smack rules grammar + their stateful parser
From
On Fri, Nov 02, 2007 at 01:50:55PM -0700, Casey Schaufler wrote:
>
> Still to come:
>
> - Final cleanup of smack_load_write and smack_cipso_write.

Hi All,

After agreeing with Casey on the "load" input grammar yesterday, here's
the final grammar and its parser (which needs more testing):

A Smack Rule in an "egrep" format is:

"^[:space:]*Subject[:space:]+Object[:space:]+[rwxaRWXA-]+[:space:]*\n"

where Subject/Object strings are in the form:

"^[^/[:space:][:cntrl:]]{1,SMK_MAXLEN}$"
Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
---
Bashv3 builtin "echo" behaves very strangely to -EINVAL. It sends all
the buffers that causes -EINVAL again in subsequent echo invocations.

i.e.
echo "Invalid Rule" > /smack/load # -EINVAL returned
echo "Valid Rule" > /smack/load
In seconod iteration, echo sends the first invalid buffer again
then sends the new one. This causes a
"Invalid Rule\nValid Rule" buffer sent to write().

IMHO, this is a bug in builtin echo. The external /bin/echo doesn't
cause such strange behaviour.

diff --git a/security/smack/smack.h b/security/smack/smack.h
index e0b7d26..8dcdb79 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -219,4 +219,16 @@ static inline char *smk_of_inode(const struct inode *isp)
return sip->smk_inode;
}

+static inline int isblank(char c)
+{
+ return (c == ' ' || c == '\t');
+}
+
+#define swap(x, y, type) \
+do { \
+ type tmp = x; \
+ x = y; \
+ y = tmp; \
+} while (0); \
+
#endif /* _SECURITY_SMACK_H */
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 3572ae5..0b1b530 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -25,6 +25,7 @@
#include <net/netlabel.h>
#include <net/cipso_ipv4.h>
#include <linux/seq_file.h>
+#include <linux/ctype.h>
#include "smack.h"

/*
@@ -67,6 +68,39 @@ struct smk_list_entry *smack_list;
#define SEQ_READ_FINISHED 1

/*
+ * Disable concurrent writing open() operations
+ */
+static struct semaphore smack_write_sem;
+
+/*
+ * States for parsing /smack/load rules
+ */
+enum load_state {
+ bol = 0, /* At Beginning Of Line */
+ subject = 1, /* At a "subject" token */
+ object = 2, /* At an "object" token */
+ access = 3, /* At an "access" token */
+ newline = 4, /* At end Of Line */
+ blank = 5, /* At a space or tab */
+};
+
+/*
+ * Represent current parsing state of /smack/load. Struct
+ * also stores data needed between an open-release session's
+ * multiple write() calls
+ */
+static struct smack_load_state {
+ enum load_state state; /* Current FSM parsing state */
+ enum load_state prevstate; /* Previous FSM state */
+ struct smack_rule rule; /* Rule to be loaded */
+ int label_len; /* Subject/Object labels length so far */
+ char subject[SMK_LABELLEN]; /* Subject label */
+ char object[SMK_LABELLEN]; /* Object label */
+ int access; /* Bool, parsed an "access" token ? */
+} *load_state;
+
+
+/*
* Seq_file read operations for /smack/load
*/

@@ -131,12 +165,43 @@ static struct seq_operations load_seq_ops = {
* @inode: inode structure representing file
* @file: "load" file pointer
*
- * Connect our load_seq_* operations with /smack/load
- * file_operations
+ * For reading, use load_seq_* seq_file reading operations.
+ * For writing, prepare a load_state struct to parse
+ * incoming rules.
*/
static int smk_open_load(struct inode *inode, struct file *file)
{
- return seq_open(file, &load_seq_ops);
+ if ((file->f_flags & O_ACCMODE) == O_RDONLY)
+ return seq_open(file, &load_seq_ops);
+
+ if (down_interruptible(&smack_write_sem))
+ return -ERESTARTSYS;
+
+ load_state = kzalloc(sizeof(struct smack_load_state), GFP_KERNEL);
+ if (!load_state)
+ return -ENOMEM;
+
+ return 0;
+}
+
+/**
+ * smk_release_load - release() for /smack/load
+ * @inode: inode structure representing file
+ * @file: "load" file pointer
+ *
+ * For a reading session, use the seq_file release
+ * implementation.
+ * Otherwise, we are at the end of a writing session so
+ * clean everything up.
+ */
+static int smk_release_load(struct inode *inode, struct file *file)
+{
+ if ((file->f_flags & O_ACCMODE) == O_RDONLY)
+ return seq_release(inode, file);
+
+ kfree(load_state);
+ up(&smack_write_sem);
+ return 0;
}

/**
@@ -174,7 +239,6 @@ static void smk_set_access(struct smack_rule *srp)
return;
}

-
/**
* smk_write_load - write() for /smack/load
* @filp: file pointer, not actually used
@@ -182,19 +246,26 @@ static void smk_set_access(struct smack_rule *srp)
* @count: bytes sent
* @ppos: where to start
*
- * Returns number of bytes written or error code, as appropriate
+ * Parse smack rules in below extended regex format:
+ * "^[:space:]*Subject[:space:]+Object[:space:]+[rwxaRWXA-]+[:space:]*\n"
+ * Where Subject/Object are: "^[^/[:space:][:cntrl:]]{1,SMK_MAXLEN}$"
+ *
+ * Handle defragmented rules over several write calls using a Finite
+ * State Machine that saves its state in the load_state structure.
*/
static ssize_t smk_write_load(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
- struct smack_rule rule;
- ssize_t rc = count;
+ struct smack_rule *rule = &load_state->rule;
+ enum load_state *state = &load_state->state;
+ enum load_state *prevstate = &load_state->prevstate;
+ int *label_len = &load_state->label_len;
+ char *subjectstr = load_state->subject;
+ char *objectstr = load_state->object;
+ int *accesstok = &load_state->access;
+ ssize_t rc = -EINVAL;
char *data = NULL;
- char subjectstr[SMK_LABELLEN];
- char objectstr[SMK_LABELLEN];
- char modestr[8];
- char *cp;
-
+ int i;

if (!capable(CAP_MAC_OVERRIDE))
return -EPERM;
@@ -208,7 +279,7 @@ static ssize_t smk_write_load(struct file *file, const char __user *buf,
* 80 characters per line ought to be enough.
*/
if (count > SMACK_LIST_MAX * 80)
- return -ENOMEM;
+ return -EFBIG;

data = kzalloc(count + 1, GFP_KERNEL);
if (data == NULL)
@@ -221,30 +292,93 @@ static ssize_t smk_write_load(struct file *file, const char __user *buf,

data[count] = '\0';

- for (cp = data - 1; cp != NULL; cp = strchr(cp + 1, '\n')) {
- if (*++cp == '\0')
+ for (i = 0; i < count && data[i]; i++) {
+ if (!isgraph(data[i]) && !isspace(data[i]))
+ goto out;
+
+ /* If a char-blank transition occurred */
+ if (isblank(data[i]) && *state != blank)
+ *prevstate = *state;
+ /* If a blank-char transition occurred */
+ if (!isblank(data[i]) && *state == blank) {
+ swap(*state, *prevstate, typeof(*state));
+ ++(*state);
+ }
+
+ if (isblank(data[i]))
+ *state = blank;
+
+ if (data[i] == '\n')
+ *state = newline;
+
+ switch (*state) {
+ case bol:
+ case subject:
+ if (*label_len >= SMK_MAXLEN)
+ goto out;
+ subjectstr[(*label_len)++] = data[i];
+ *state = subject;
+ break;
+
+ case object:
+ if (*prevstate == blank) {
+ subjectstr[*label_len] = '\0';
+ *label_len = 0;
+ *prevstate = *state = object;
+ }
+
+ if (*label_len >= SMK_MAXLEN)
+ goto out;
+ objectstr[(*label_len)++] = data[i];
break;
- if (sscanf(cp, "%23s %23s %7s\n", subjectstr, objectstr,
- modestr) != 3)
+
+ case access:
+ if (*prevstate == blank) {
+ objectstr[*label_len] = '\0';
+ *label_len = 0;
+ *prevstate = *state = access;
+ }
+
+ if (data[i] == 'r' || data[i] == 'R')
+ rule->smk_access |= MAY_READ;
+ else if (data[i] == 'w' || data[i] == 'W')
+ rule->smk_access |= MAY_WRITE;
+ else if (data[i] == 'x' || data[i] == 'X')
+ rule->smk_access |= MAY_EXEC;
+ else if (data[i] == 'a' || data[i] == 'A')
+ rule->smk_access |= MAY_APPEND;
+ else if (data[i] == '-')
+ /* No-Op, '-' is a placeholder */;
+ else
+ goto out;
+ *accesstok = 1;
break;
- rule.smk_subject = smk_import(subjectstr, 0);
- if (rule.smk_subject == NULL)
+
+ case newline:
+ if (*accesstok == 0)
+ goto out;
+
+ rule->smk_subject = smk_import(subjectstr, 0);
+ if (rule->smk_subject == NULL)
+ goto out;
+
+ rule->smk_object = smk_import(objectstr, 0);
+ if (rule->smk_object == NULL)
+ goto out;
+
+ smk_set_access(rule);
+
+ /* Reset everything, a new rule will come */
+ memset(load_state, 0, sizeof(*load_state));
break;
- rule.smk_object = smk_import(objectstr, 0);
- if (rule.smk_object == NULL)
+
+ case blank:
break;
- rule.smk_access = 0;
- if (strpbrk(modestr, "rR") != NULL)
- rule.smk_access |= MAY_READ;
- if (strpbrk(modestr, "wW") != NULL)
- rule.smk_access |= MAY_WRITE;
- if (strpbrk(modestr, "xX") != NULL)
- rule.smk_access |= MAY_EXEC;
- if (strpbrk(modestr, "aA") != NULL)
- rule.smk_access |= MAY_APPEND;
- smk_set_access(&rule);
+ }
}

+ rc = count;
+out:
kfree(data);
return rc;
}
@@ -254,7 +388,7 @@ static const struct file_operations smk_load_ops = {
.read = seq_read,
.llseek = seq_lseek,
.write = smk_write_load,
- .release = seq_release
+ .release = smk_release_load,
};

/**
@@ -924,6 +1058,7 @@ static int __init init_smk_fs(void)
}
}

+ sema_init(&smack_write_sem, 1);
smk_cipso_doi();

return err;
--
Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com
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