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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: Lingzhu 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: Matt Fleming <matt.fleming@intel.com>
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94a193fb73
commit
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1 changed files with 44 additions and 5 deletions
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@ -79,6 +79,7 @@
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#include <linux/device.h>
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#include <linux/device.h>
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#include <linux/slab.h>
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#include <linux/slab.h>
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#include <linux/pstore.h>
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#include <linux/pstore.h>
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#include <linux/ctype.h>
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#include <linux/fs.h>
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#include <linux/fs.h>
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#include <linux/ramfs.h>
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#include <linux/ramfs.h>
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@ -900,6 +901,48 @@ static struct inode *efivarfs_get_inode(struct super_block *sb,
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return inode;
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return inode;
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}
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}
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/*
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* Return true if 'str' is a valid efivarfs filename of the form,
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*
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* VariableName-12345678-1234-1234-1234-1234567891bc
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*/
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static bool efivarfs_valid_name(const char *str, int len)
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{
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static const char dashes[GUID_LEN] = {
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[8] = 1, [13] = 1, [18] = 1, [23] = 1
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};
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const char *s = str + len - GUID_LEN;
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int i;
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/*
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* We need a GUID, plus at least one letter for the variable name,
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* plus the '-' separator
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*/
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if (len < GUID_LEN + 2)
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return false;
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/* GUID should be right after the first '-' */
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if (s - 1 != strchr(str, '-'))
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return false;
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/*
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* Validate that 's' is of the correct format, e.g.
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*
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* 12345678-1234-1234-1234-123456789abc
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*/
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for (i = 0; i < GUID_LEN; i++) {
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if (dashes[i]) {
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if (*s++ != '-')
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return false;
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} else {
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if (!isxdigit(*s++))
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return false;
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}
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}
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return true;
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}
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static void efivarfs_hex_to_guid(const char *str, efi_guid_t *guid)
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static void efivarfs_hex_to_guid(const char *str, efi_guid_t *guid)
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{
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{
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guid->b[0] = hex_to_bin(str[6]) << 4 | hex_to_bin(str[7]);
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guid->b[0] = hex_to_bin(str[6]) << 4 | hex_to_bin(str[7]);
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@ -928,11 +971,7 @@ static int efivarfs_create(struct inode *dir, struct dentry *dentry,
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struct efivar_entry *var;
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struct efivar_entry *var;
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int namelen, i = 0, err = 0;
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int namelen, i = 0, err = 0;
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/*
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if (!efivarfs_valid_name(dentry->d_name.name, dentry->d_name.len))
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* We need a GUID, plus at least one letter for the variable name,
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* plus the '-' separator
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*/
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if (dentry->d_name.len < GUID_LEN + 2)
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return -EINVAL;
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return -EINVAL;
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inode = efivarfs_get_inode(dir->i_sb, dir, mode, 0);
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inode = efivarfs_get_inode(dir->i_sb, dir, mode, 0);
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