Commit 168b7173 authored by Steve Grubb's avatar Steve Grubb Committed by David Woodhouse
Browse files

AUDIT: Clean up logging of untrusted strings 



* If vsnprintf returns -1, it will mess up the sk buffer space accounting. 
This is fixed by not calling skb_put with bogus len values.

* audit_log_hex was a loop that called audit_log_vformat with %02X for each 
character. This is very inefficient since conversion from unsigned character 
to Ascii representation is essentially masking, shifting, and byte lookups. 
Also, the length of the converted string is well known - it's twice the 
original. Fixed by rewriting the function.

* audit_log_untrustedstring had no comments. This makes it hard for 
someone to understand what the string format will be.

* audit_log_d_path was never fixed to use untrustedstring. This could mess
up user space parsers. This was fixed to make a temp buffer, call d_path, 
and log temp buffer using untrustedstring. 

From: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: default avatarDavid Woodhouse <dwmw2@infradead.org>
parent 209aba03

kernel/audit.c

+48 −23
Original line number Diff line number Diff line
@@ -692,7 +692,8 @@ static void audit_log_vformat(struct audit_buffer *ab, const char *fmt, 
			goto out;

		len = vsnprintf(skb->tail, avail, fmt, args2);

	}

	skb_put(skb, (len < avail) ? len : avail);

	if (len > 0)

		skb_put(skb, len);

out:

	return;

}
@@ -710,20 +711,47 @@ void audit_log_format(struct audit_buffer *ab, const char *fmt, ...) 
	va_end(args);

}



void audit_log_hex(struct audit_buffer *ab, const unsigned char *buf, size_t len)

/* This function will take the passed buf and convert it into a string of

 * ascii hex digits. The new string is placed onto the skb. */

void audit_log_hex(struct audit_buffer *ab, const unsigned char *buf, 

		size_t len)

{

	int i;

	int i, avail, new_len;

	unsigned char *ptr;

	struct sk_buff *skb;

	static const unsigned char *hex = "0123456789ABCDEF";



	BUG_ON(!ab->skb);

	skb = ab->skb;

	avail = skb_tailroom(skb);

	new_len = len<<1;

	if (new_len >= avail) {

		/* Round the buffer request up to the next multiple */

		new_len = AUDIT_BUFSIZ*(((new_len-avail)/AUDIT_BUFSIZ) + 1);

		avail = audit_expand(ab, new_len);

		if (!avail)

			return;

	}



	for (i=0; i<len; i++)

		audit_log_format(ab, "%02x", buf[i]);

	ptr = skb->tail;

	for (i=0; i<len; i++) {

		*ptr++ = hex[(buf[i] & 0xF0)>>4]; /* Upper nibble */

		*ptr++ = hex[buf[i] & 0x0F];	  /* Lower nibble */

	}

	*ptr = 0;

	skb_put(skb, len << 1); /* new string is twice the old string */

}



/* This code will escape a string that is passed to it if the string

 * contains a control character, unprintable character, double quote mark, 

 * or a space. Unescaped strings will start and end with a double quote mark.

 * Strings that are escaped are printed in hex (2 digits per char). */

void audit_log_untrustedstring(struct audit_buffer *ab, const char *string)

{

	const unsigned char *p = string;



	while (*p) {

		if (*p == '"' || *p == ' ' || *p < 0x20 || *p > 0x7f) {

		if (*p == '"' || *p < 0x21 || *p > 0x7f) {

			audit_log_hex(ab, string, strlen(string));

			return;

		}
@@ -732,31 +760,28 @@ void audit_log_untrustedstring(struct audit_buffer *ab, const char *string) 
	audit_log_format(ab, "\"%s\"", string);

}





/* This is a helper-function to print the d_path without using a static

 * buffer or allocating another buffer in addition to the one in

 * audit_buffer. */

/* This is a helper-function to print the escaped d_path */

void audit_log_d_path(struct audit_buffer *ab, const char *prefix,

		      struct dentry *dentry, struct vfsmount *vfsmnt)

{

	char *p;

	struct sk_buff *skb = ab->skb;

	int  len, avail;

	char *p, *path;



	if (prefix)

		audit_log_format(ab, " %s", prefix);



	avail = skb_tailroom(skb);

	p = d_path(dentry, vfsmnt, skb->tail, avail);

	if (IS_ERR(p)) {

	/* We will allow 11 spaces for ' (deleted)' to be appended */

	path = kmalloc(PATH_MAX+11, GFP_KERNEL);

	if (!path) {

		audit_log_format(ab, "<no memory>");

		return;

	}

	p = d_path(dentry, vfsmnt, path, PATH_MAX+11);

	if (IS_ERR(p)) { /* Should never happen since we send PATH_MAX */

		/* FIXME: can we save some information here? */

		audit_log_format(ab, "<too long>");

	} else {

		/* path isn't at start of buffer */

		len = ((char *)skb->tail + avail - 1) - p;

		memmove(skb->tail, p, len);

		skb_put(skb, len);

	}

	} else 

		audit_log_untrustedstring(ab, p);

	kfree(path);

}



/* Remove queued messages from the audit_txlist and send them to user space. */

CRA Git | Maintained and supported by SUSTech CRA and CCSE