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,
* Ensure the GUID only contains hexadecimal digits and dashes.
* 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>
---
v2: Use Al's much improve filename parsing code and make
efivarfs_valid_name() return the more natural boolean type.
drivers/firmware/efivars.c | 49 +++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 44 insertions(+), 5 deletions(-)
diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 371c441..868cea5 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -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);
--
1.7.11.7
--
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