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Date: Wed, 4 Mar 2020 16:49:36 +0100
From: Vladis Dronov <vdronov@...hat.com>
To: Ard Biesheuvel <ardb@...nel.org>, linux-efi@...r.kernel.org,
joeyli <jlee@...e.com>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH v2] efi: fix a race and a buffer overflow while reading efivars via sysfs
There is a race and a buffer overflow corrupting a kernel memory while
reading an efi variable with a size more than 1024 bytes via the older
sysfs method. This happens because accessing struct efi_variable in
efivar_{attr,size,data}_read() and friends is not protected from
a concurrent access leading to a kernel memory corruption and, at best,
to a crash. The race scenario is the following:
CPU0: CPU1:
efivar_attr_read()
var->DataSize = 1024;
efivar_entry_get(... &var->DataSize)
down_interruptible(&efivars_lock)
efivar_attr_read() // same efi var
var->DataSize = 1024;
efivar_entry_get(... &var->DataSize)
down_interruptible(&efivars_lock)
virt_efi_get_variable()
// returns EFI_BUFFER_TOO_SMALL but
// var->DataSize is set to a real
// var size more than 1024 bytes
up(&efivars_lock)
virt_efi_get_variable()
// called with var->DataSize set
// to a real var size, returns
// successfully and overwrites
// a 1024-bytes kernel buffer
up(&efivars_lock)
This can be reproduced by concurrent reading of an efi variable which size
is more than 1024 bytes:
ts# for cpu in $(seq 0 $(nproc --ignore=1)); do ( taskset -c $cpu \
cat /sys/firmware/efi/vars/KEKDefault*/size & ) ; done
Fix this by using a local variable for a var's data buffer size so it
does not get overwritten. Also add a sanity check to efivar_store_raw().
Reported-by: Bob Sanders <bob.sanders@....com> and the LTP testsuite
Signed-off-by: Vladis Dronov <vdronov@...hat.com>
---
drivers/firmware/efi/efi-pstore.c | 2 +-
drivers/firmware/efi/efivars.c | 32 ++++++++++++++++++++++---------
drivers/firmware/efi/vars.c | 2 +-
3 files changed, 25 insertions(+), 11 deletions(-)
diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index 9ea13e8d12ec..e4767a7ce973 100644
--- a/drivers/firmware/efi/efi-pstore.c
+++ b/drivers/firmware/efi/efi-pstore.c
@@ -161,7 +161,7 @@ static int efi_pstore_scan_sysfs_exit(struct efivar_entry *pos,
*
* @record: pstore record to pass to callback
*
- * You MUST call efivar_enter_iter_begin() before this function, and
+ * You MUST call efivar_entry_iter_begin() before this function, and
* efivar_entry_iter_end() afterwards.
*
*/
diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
index 7576450c8254..16a617f9c5cf 100644
--- a/drivers/firmware/efi/efivars.c
+++ b/drivers/firmware/efi/efivars.c
@@ -83,13 +83,16 @@ static ssize_t
efivar_attr_read(struct efivar_entry *entry, char *buf)
{
struct efi_variable *var = &entry->var;
+ unsigned long size = sizeof(var->Data);
char *str = buf;
+ int ret;
if (!entry || !buf)
return -EINVAL;
- var->DataSize = 1024;
- if (efivar_entry_get(entry, &var->Attributes, &var->DataSize, var->Data))
+ ret = efivar_entry_get(entry, &var->Attributes, &size, var->Data);
+ var->DataSize = size;
+ if (ret)
return -EIO;
if (var->Attributes & EFI_VARIABLE_NON_VOLATILE)
@@ -116,13 +119,16 @@ static ssize_t
efivar_size_read(struct efivar_entry *entry, char *buf)
{
struct efi_variable *var = &entry->var;
+ unsigned long size = sizeof(var->Data);
char *str = buf;
+ int ret;
if (!entry || !buf)
return -EINVAL;
- var->DataSize = 1024;
- if (efivar_entry_get(entry, &var->Attributes, &var->DataSize, var->Data))
+ ret = efivar_entry_get(entry, &var->Attributes, &size, var->Data);
+ var->DataSize = size;
+ if (ret)
return -EIO;
str += sprintf(str, "0x%lx\n", var->DataSize);
@@ -133,12 +139,15 @@ static ssize_t
efivar_data_read(struct efivar_entry *entry, char *buf)
{
struct efi_variable *var = &entry->var;
+ unsigned long size = sizeof(var->Data);
+ int ret;
if (!entry || !buf)
return -EINVAL;
- var->DataSize = 1024;
- if (efivar_entry_get(entry, &var->Attributes, &var->DataSize, var->Data))
+ ret = efivar_entry_get(entry, &var->Attributes, &size, var->Data);
+ var->DataSize = size;
+ if (ret)
return -EIO;
memcpy(buf, var->Data, var->DataSize);
@@ -199,6 +208,9 @@ efivar_store_raw(struct efivar_entry *entry, const char *buf, size_t count)
u8 *data;
int err;
+ if (!entry || !buf)
+ return -EINVAL;
+
if (in_compat_syscall()) {
struct compat_efi_variable *compat;
@@ -250,14 +262,16 @@ efivar_show_raw(struct efivar_entry *entry, char *buf)
{
struct efi_variable *var = &entry->var;
struct compat_efi_variable *compat;
+ unsigned long datasize = sizeof(var->Data);
size_t size;
+ int ret;
if (!entry || !buf)
return 0;
- var->DataSize = 1024;
- if (efivar_entry_get(entry, &entry->var.Attributes,
- &entry->var.DataSize, entry->var.Data))
+ ret = efivar_entry_get(entry, &var->Attributes, &datasize, var->Data);
+ var->DataSize = size;
+ if (ret)
return -EIO;
if (in_compat_syscall()) {
diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 436d1776bc7b..5f2a4d162795 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -1071,7 +1071,7 @@ EXPORT_SYMBOL_GPL(efivar_entry_iter_end);
* entry on the list. It is safe for @func to remove entries in the
* list via efivar_entry_delete().
*
- * You MUST call efivar_enter_iter_begin() before this function, and
+ * You MUST call efivar_entry_iter_begin() before this function, and
* efivar_entry_iter_end() afterwards.
*
* It is possible to begin iteration from an arbitrary entry within
--
2.20.1
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