diff options
author | Vladis Dronov <vdronov@redhat.com> | 2020-03-08 09:08:54 +0100 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2020-03-08 09:56:34 +0100 |
commit | 286d3250c9d6437340203fb64938bea344729a0e (patch) | |
tree | 28eee8f847ed45308de8bea0a26c772d55d384c4 | |
parent | 61a09258f2e5b48ad0605131cae9a33ce4d01a9d (diff) | |
download | linux-286d3250c9d6437340203fb64938bea344729a0e.tar.bz2 |
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.
Fixes: e14ab23dde12b80d ("efivars: efivar_entry API")
Reported-by: Bob Sanders <bob.sanders@hpe.com> and the LTP testsuite
Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200305084041.24053-2-vdronov@redhat.com
Link: https://lore.kernel.org/r/20200308080859.21568-24-ardb@kernel.org
-rw-r--r-- | drivers/firmware/efi/efivars.c | 29 |
1 files changed, 20 insertions, 9 deletions
diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c index 7576450c8254..69f13bc4b931 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); @@ -250,14 +259,16 @@ 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 (in_compat_syscall()) { |