From 47f531e8ba3bc3901a0c493f4252826c41dea1a1 Mon Sep 17 00:00:00 2001 From: Matt Fleming Date: Thu, 31 Jan 2013 19:02:03 +0000 Subject: [PATCH] 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 Cc: Matthew Garrett Cc: Jeremy Kerr Cc: Al Viro Signed-off-by: Matt Fleming --- 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 371c44129525..868cea5cd4b8 100644 --- a/drivers/firmware/efivars.c +++ b/drivers/firmware/efivars.c @@ -79,6 +79,7 @@ #include #include #include +#include #include #include @@ -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);