From: Matt Fleming <matt.fleming@xxxxxxxxx>
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@xxxxxxxxxx>
Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
Cc: Jeremy Kerr <jeremy.kerr@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Matt Fleming <matt.fleming@xxxxxxxxx>
---
drivers/firmware/efivars.c | 55 +++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 50 insertions(+), 5 deletions(-)
diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 371c441..a4fa409 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -900,6 +900,55 @@ static struct inode *efivarfs_get_inode(struct super_block *sb,
return inode;
}
+/*
+ * Return 1 if 'str' is a valid efivarfs filename of the form,
+ *
+ * VariableName-12345678-1234-1234-1234-1234567891bc
+ */
+static int efivarfs_valid_name(const char *str, int len)
+{
+ const char *s;
+ int i, j;
+ int ranges[2][5] = {
+ { 0, 9, 14, 19, 24 },
+ { 8, 13, 18, 23, 36 }
+ };
+
+ /*
+ * We need a GUID, plus at least one letter for the variable name,
+ * plus the '-' separator
+ */
+ if (len < GUID_LEN + 2)
+ return 0;
+
+ s = strchr(str, '-');
+ if (!s)
+ return 0;
+
+ s++; /* Skip '-' */
+
+ /* Ensure we have enough characters for a GUID */
+ if (len - (s - str) != GUID_LEN)
+ return 0;
+
+ /*
+ * Validate that 's' is of the correct format, e.g.
+ *
+ * 12345678-1234-1234-1234-123456789abc
+ */
+ for (i = 0; i < 5; i++) {
+ for (j = ranges[0][i]; j < ranges[1][i]; j++) {
+ if (hex_to_bin(s[j]) < 0)
+ return 0;
+ }
+
+ if (j < GUID_LEN && s[j] != '-')
+ return 0;
+ }
+
+ return 1;
+}
+
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 +977,7 @@ 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);
--
1.7.11.7
--
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