From e8e61d5e2676e78594ad4f173b113a082a59ec84 Mon Sep 17 00:00:00 2001 From: Matt Fleming Date: Fri, 1 Mar 2013 14:49:12 +0000 Subject: [PATCH] efivars: explicitly calculate length of VariableName commit ec50bd32f1672d38ddce10fb1841cbfda89cfe9a upstream. It's not wise to assume VariableNameSize represents the length of VariableName, as not all firmware updates VariableNameSize in the same way (some don't update it at all if EFI_SUCCESS is returned). There are even implementations out there that update VariableNameSize with values that are both larger than the string returned in VariableName and smaller than the buffer passed to GetNextVariableName(), which resulted in the following bug report from Michael Schroeder, > On HP z220 system (firmware version 1.54), some EFI variables are > incorrectly named : > > ls -d /sys/firmware/efi/vars/*8be4d* | grep -v -- -8be returns > /sys/firmware/efi/vars/dbxDefault-pport8be4df61-93ca-11d2-aa0d-00e098032b8c > /sys/firmware/efi/vars/KEKDefault-pport8be4df61-93ca-11d2-aa0d-00e098032b8c > /sys/firmware/efi/vars/SecureBoot-pport8be4df61-93ca-11d2-aa0d-00e098032b8c > /sys/firmware/efi/vars/SetupMode-Information8be4df61-93ca-11d2-aa0d-00e098032b8c The issue here is that because we blindly use VariableNameSize without verifying its value, we can potentially read garbage values from the buffer containing VariableName if VariableNameSize is larger than the length of VariableName. Since VariableName is a string, we can calculate its size by searching for the terminating NULL character. [Backported for 3.8-stable. Removed workqueue code added in a93bc0c 3.9-rc1.] Reported-by: Frederic Crozat Cc: Matthew Garrett Cc: Josh Boyer Cc: Michael Schroeder Cc: Lee, Chun-Yi Cc: Lingzhu Xiang Cc: Seiji Aguchi Signed-off-by: Matt Fleming Signed-off-by: Lingzhu Xiang Reviewed-by: CAI Qian Signed-off-by: Greg Kroah-Hartman --- drivers/firmware/efivars.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c index e1d6253a8c6f..1955f5f87c6b 100644 --- a/drivers/firmware/efivars.c +++ b/drivers/firmware/efivars.c @@ -1669,6 +1669,31 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj, return count; } +/* + * Returns the size of variable_name, in bytes, including the + * terminating NULL character, or variable_name_size if no NULL + * character is found among the first variable_name_size bytes. + */ +static unsigned long var_name_strnsize(efi_char16_t *variable_name, + unsigned long variable_name_size) +{ + unsigned long len; + efi_char16_t c; + + /* + * The variable name is, by definition, a NULL-terminated + * string, so make absolutely sure that variable_name_size is + * the value we expect it to be. If not, return the real size. + */ + for (len = 2; len <= variable_name_size; len += sizeof(c)) { + c = variable_name[(len / sizeof(c)) - 1]; + if (!c) + break; + } + + return min(len, variable_name_size); +} + /* * Let's not leave out systab information that snuck into * the efivars driver @@ -1912,6 +1937,8 @@ int register_efivars(struct efivars *efivars, &vendor_guid); switch (status) { case EFI_SUCCESS: + variable_name_size = var_name_strnsize(variable_name, + variable_name_size); efivar_create_sysfs_entry(efivars, variable_name_size, variable_name, -- 2.39.5