Commit 47f531e8 authored by Matt Fleming's avatar Matt Fleming
Browse files

efivarfs: Validate filenames much more aggressively 



The only thing that efivarfs does to enforce a valid filename is
ensure that the name isn't too short. We need to strongly sanitise any
filenames, not least because variable creation is delayed until
efivarfs_file_write(), which means we can't rely on the firmware to
inform us of an invalid name, because if the file is never written to
we'll never know it's invalid.

Perform a couple of steps before agreeing to create a new file,

  * hex_to_bin() returns a value indicating whether or not it was able
    to convert its arguments to a binary representation - we should
    check it.

  * Ensure that the GUID portion of the filename is the correct length
    and format.

  * The variable name portion of the filename needs to be at least one
    character in size.

Reported-by: default avatarLingzhu Xiang <lxiang@redhat.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Jeremy Kerr <jeremy.kerr@canonical.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarMatt Fleming <matt.fleming@intel.com>
parent 94a193fb

drivers/firmware/efivars.c

+44 −5
Original line number Diff line number Diff line
@@ -79,6 +79,7 @@ 
#include <linux/device.h>

#include <linux/slab.h>

#include <linux/pstore.h>

#include <linux/ctype.h>



#include <linux/fs.h>

#include <linux/ramfs.h>
@@ -900,6 +901,48 @@ static struct inode *efivarfs_get_inode(struct super_block *sb, 
	return inode;

}



/*

 * Return true if 'str' is a valid efivarfs filename of the form,

 *

 *	VariableName-12345678-1234-1234-1234-1234567891bc

 */

static bool efivarfs_valid_name(const char *str, int len)

{

	static const char dashes[GUID_LEN] = {

		[8] = 1, [13] = 1, [18] = 1, [23] = 1

	};

	const char *s = str + len - GUID_LEN;

	int i;



	/*

	 * We need a GUID, plus at least one letter for the variable name,

	 * plus the '-' separator

	 */

	if (len < GUID_LEN + 2)

		return false;



	/* GUID should be right after the first '-' */

	if (s - 1 != strchr(str, '-'))

		return false;



	/*

	 * Validate that 's' is of the correct format, e.g.

	 *

	 *	12345678-1234-1234-1234-123456789abc

	 */

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

		if (dashes[i]) {

			if (*s++ != '-')

				return false;

		} else {

			if (!isxdigit(*s++))

				return false;

		}

	}



	return true;

}



static void efivarfs_hex_to_guid(const char *str, efi_guid_t *guid)

{

	guid->b[0] = hex_to_bin(str[6]) << 4 | hex_to_bin(str[7]);
@@ -928,11 +971,7 @@ static int efivarfs_create(struct inode *dir, struct dentry *dentry, 
	struct efivar_entry *var;

	int namelen, i = 0, err = 0;



	/*

	 * We need a GUID, plus at least one letter for the variable name,

	 * plus the '-' separator

	 */

	if (dentry->d_name.len < GUID_LEN + 2)

	if (!efivarfs_valid_name(dentry->d_name.name, dentry->d_name.len))

		return -EINVAL;



	inode = efivarfs_get_inode(dir->i_sb, dir, mode, 0);

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