commit 286d3250c9d6437340203fb64938bea344729a0e upstream.
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.
Fixes: e14ab23dde12b80d ("efivars: efivar_entry API")
Reported-by: Bob Sanders <bob.sanders@xxxxxxx> and the LTP testsuite
Signed-off-by: Vladis Dronov <vdronov@xxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200305084041.24053-2-vdronov@xxxxxxxxxx
Link: https://lore.kernel.org/r/20200308080859.21568-24-ardb@xxxxxxxxxx
---
drivers/firmware/efi/efivars.c | 29 ++++++++++++++++++++---------
1 file changed, 20 insertions(+), 9 deletions(-)
diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
index 3e626fd9bd4e..c8688490f148 100644
--- a/drivers/firmware/efi/efivars.c
+++ b/drivers/firmware/efi/efivars.c
@@ -139,13 +139,16 @@ 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)
@@ -172,13 +175,16 @@ 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);
@@ -189,12 +195,15 @@ 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);
@@ -314,14 +323,16 @@ 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 = datasize;
+ if (ret)
return -EIO;
if (is_compat()) {
--
2.20.1
