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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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