Re: [PATCH] bfa: avoid buffer overrun for 12-byte model name

[Jim Meyering <jim@meyering.net>]

Jim Meyering wrote:
> Jim Meyering wrote:
>> Krishna Gudipati wrote:
>>>> -----Original Message-----
>>>> From: Jim Meyering [mailto:jim@meyering.net]
>>>> Sent: Monday, August 20, 2012 9:55 AM
>>>> To: linux-kernel@vger.kernel.org
>>>> Cc: Jim Meyering; Jing Huang; Krishna Gudipati; James E.J. Bottomley; linux-
>>>> scsi@vger.kernel.org
>>>> Subject: [PATCH] bfa: avoid buffer overrun for 12-byte model name
>>>>
>>>> From: Jim Meyering <meyering@redhat.com>
>>>>
>>>> we use strncpy to copy a model name of length up to 15 (16, if you count the
>>>> NUL), into a buffer of size 12 (BFA_FCS_PORT_SYMBNAME_MODEL_SZ).
>>>> However, strncpy does not always NUL-terminate, so whenever the original
>>>> model string has strlen >= 12, the following strncat reads beyond end of the -
>>>> >sym_name buffer as it attempts to find end of string.
>>>>
>>>> bfa_fcs_fabric_psymb_init(struct bfa_fcs_fabric_s *fabric) {
>>>> 	bfa_ioc_get_adapter_model(&fabric->fcs->bfa->ioc, model);
>>>> 	...
>>>> 	strncpy((char *)&port_cfg->sym_name, model,
>>>> 		BFA_FCS_PORT_SYMBNAME_MODEL_SZ);
>>>> 	strncat((char *)&port_cfg->sym_name,
>>>> BFA_FCS_PORT_SYMBNAME_SEPARATOR,
>>>> 		sizeof(BFA_FCS_PORT_SYMBNAME_SEPARATOR));
>>>> 	...
>>>>
>>>> bfa_ioc_get_adapter_model(struct bfa_ioc_s *ioc, char *model) {
>>>> 	struct bfi_ioc_attr_s	*ioc_attr;
>>>>
>>>> 	WARN_ON(!model);
>>>> 	memset((void *)model, 0, BFA_ADAPTER_MODEL_NAME_LEN);
>>>>
>>>> BFA_ADAPTER_MODEL_NAME_LEN = 16
>>>>
>>>> Signed-off-by: Jim Meyering <meyering@redhat.com>
>>>> ---
>>>>  drivers/scsi/bfa/bfa_fcs.c | 1 +
>>>>  1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/scsi/bfa/bfa_fcs.c b/drivers/scsi/bfa/bfa_fcs.c index
>>>> eaac57e..3329493 100644
>>>> --- a/drivers/scsi/bfa/bfa_fcs.c
>>>> +++ b/drivers/scsi/bfa/bfa_fcs.c
>>>> @@ -713,6 +713,7 @@ bfa_fcs_fabric_psymb_init(struct bfa_fcs_fabric_s
>>>> *fabric)
>>>>  	/* Model name/number */
>>>>  	strncpy((char *)&port_cfg->sym_name, model,
>>>>  		BFA_FCS_PORT_SYMBNAME_MODEL_SZ);
>>>> +	port_cfg->sym_name[BFA_FCS_PORT_SYMBNAME_MODEL_SZ - 1]
>>>> = 0;
>>>>  	strncat((char *)&port_cfg->sym_name,
>>>> BFA_FCS_PORT_SYMBNAME_SEPARATOR,
>>>>  		sizeof(BFA_FCS_PORT_SYMBNAME_SEPARATOR));
>>>
>>> Nacked-by: Krishna Gudipati <kgudipat@brocade.com>
>>>
>>> Hi Jim,
>>>
>>> This model number is of length 12 bytes and the logic added here will
>>> reset the model last byte.
>>> In addition strncat does not need the src to be null terminated, the
>>> change does not compile even.
>>> NACK to this change.
>>
>> Hi Krishna,
>>
>> Thanks for the quick feedback and sorry the patch wasn't quite right.
>> However, the log is accurate: there is at least a theoretical problem
>> when the string in "model" (a buffer of size 16 bytes) has strlen >= 12.
>> While strncat does not require that its second argument be NUL-terminated,
>> the first one (the destination) must be.  Otherwise, it has no way to
>> determine the end of the string to which it must append the source bytes.
>
> Ping?
> In case it wasn't clear, there *is* a risk of buffer overflow,
> which happens when strncpy makes it so strncat's destination
> is not NUL terminated.
>
> If you require support for 12-byte model numbers, then
> you'll have to increase the length of that buffer
> (BFA_FCS_PORT_SYMBNAME_MODEL_SZ) to at least 13.
>
> I've just rebased, and thus confirmed that the patches still apply.
>
>> Here is a v2 patch to which I've added the requisite (char*) cast.
>> However, this whole function is rather unreadable due to the
>> repetition (12 times!) of "(char *)&port_cfg->sym_name".
>> In case someone prefers to factor out that repetition,
>> I've appended a larger, v3 patch to do that.

Taking Andi's advice, I've made the offending code use
strlcpy in place of strncpy.  More importantly, I've fixed
the same bug also in the following, nearly identical function.

-- >8 --

Two functions have this problem:
  bfa_fcs_fabric_psymb_init
  bfa_fcs_fabric_nsymb_init
They use strncpy to copy a model name of length up to 15 (16, if you
count the NUL), into a buffer of size 12 (BFA_FCS_PORT_SYMBNAME_MODEL_SZ).
However, strncpy does not always NUL-terminate, so whenever the original
model string has strlen >= 12, the following strncat reads beyond end
of the ->sym_name buffer as it attempts to find end of string.
Instead, use strlcpy, which does guarantee NUL-termination.

bfa_fcs_fabric_psymb_init(struct bfa_fcs_fabric_s *fabric)
{
	bfa_ioc_get_adapter_model(&fabric->fcs->bfa->ioc, model);
	...
	strncpy((char *)&port_cfg->sym_name, model,
		BFA_FCS_PORT_SYMBNAME_MODEL_SZ);
	strncat((char *)&port_cfg->sym_name, BFA_FCS_PORT_SYMBNAME_SEPARATOR,
		sizeof(BFA_FCS_PORT_SYMBNAME_SEPARATOR));
	...

bfa_ioc_get_adapter_model(struct bfa_ioc_s *ioc, char *model)
{
	struct bfi_ioc_attr_s	*ioc_attr;

	WARN_ON(!model);
	memset((void *)model, 0, BFA_ADAPTER_MODEL_NAME_LEN);

BFA_ADAPTER_MODEL_NAME_LEN = 16

Signed-off-by: Jim Meyering <jim@meyering.net>
---
 drivers/scsi/bfa/bfa_fcs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/bfa/bfa_fcs.c b/drivers/scsi/bfa/bfa_fcs.c
index d428808..c7f476c 100644
--- a/drivers/scsi/bfa/bfa_fcs.c
+++ b/drivers/scsi/bfa/bfa_fcs.c
@@ -837,7 +837,7 @@ bfa_fcs_fabric_psymb_init(struct bfa_fcs_fabric_s *fabric)
 	bfa_ioc_get_adapter_model(&fabric->fcs->bfa->ioc, model);

 	/* Model name/number */
-	strncpy((char *)&port_cfg->sym_name, model,
+	strlcpy((char *)&port_cfg->sym_name, model,
 		BFA_FCS_PORT_SYMBNAME_MODEL_SZ);
 	strncat((char *)&port_cfg->sym_name, BFA_FCS_PORT_SYMBNAME_SEPARATOR,
 		sizeof(BFA_FCS_PORT_SYMBNAME_SEPARATOR));
@@ -898,7 +898,7 @@ bfa_fcs_fabric_nsymb_init(struct bfa_fcs_fabric_s *fabric)
 	bfa_ioc_get_adapter_model(&fabric->fcs->bfa->ioc, model);

 	/* Model name/number */
-	strncpy((char *)&port_cfg->node_sym_name, model,
+	strlcpy((char *)&port_cfg->node_sym_name, model,
 		BFA_FCS_PORT_SYMBNAME_MODEL_SZ);
 	strncat((char *)&port_cfg->node_sym_name,
 			BFA_FCS_PORT_SYMBNAME_SEPARATOR,
--
1.8.0.rc2