On (14/08/13 20:32), Michal Židek wrote:
On 08/14/2013 08:13 PM, Simo Sorce wrote:
>On Wed, 2013-08-14 at 19:41 +0200, Michal Židek wrote:
>>
>>+ strs_offset = offsetof(struct sss_mc_grp_data, strs);
>> data = (struct sss_mc_grp_data *)rec->data;
>>+ /* Integrity check
>>+ * - name_len cannot be longer than all strings
>>+ * - data->name cannot point outside strings
>>+ * - all strings must be within data_table */
>>+ if (name_len > data->strs_len
>>+ || data->name > strs_offset + data->strs_len
>>+ || (uint8_t *)data->strs + data->strs_len > max_addr) {
>>+ ret = ENOENT;
>>+ goto done;
>>+ }
>>+
>
>Sorry Michal, I noticed this before but forgot to comment on it.
>
>I think the second check should be:
> || (data->name + name_len) > (strs_offset + data->strs_len)
>
>Otherwise you could run out of bounds in the strcmp.
You are right.
>
>Also given this same complex check is done in 2 places maybe it can make
>sense to have a common utility function or a macro to do the check.
>
>The other patches look good.
>
>Simo.
>
Thanks for the review.
New patches are attached.
Michal
I tested sssd with your patches and I found few issues.
From 8544f2eab5d20d082cdb3788ef07ebaa3b3157c5 Mon Sep 17 00:00:00
2001
From: Michal Zidek <mzidek(a)redhat.com>
Date: Mon, 12 Aug 2013 19:29:56 +0200
Subject: [PATCH 1/3] mmap_cache: Check data->name value in client code
data->name value must be checked to prevent segfaults in
case of corrupted memory cache.
resolves:
https://fedorahosted.org/sssd/ticket/2018
---
src/sss_client/nss_mc_group.c | 18 ++++++++++++++++++
src/sss_client/nss_mc_passwd.c | 19 +++++++++++++++++++
2 files changed, 37 insertions(+)
diff --git a/src/sss_client/nss_mc_group.c b/src/sss_client/nss_mc_group.c
... snip
..
+ strs_offset = offsetof(struct sss_mc_grp_data, strs);
data = (struct sss_mc_grp_data *)rec->data;
+ /* Integrity check
+ * - name_len cannot be longer than all strings
+ * - data->name cannot point outside strings
+ * - all strings must be within data_table */
+ if (name_len > data->strs_len
+ || (data->name + name_len) > (strs_offset + data->strs_len)
+ || (uint8_t *)data->strs + data->strs_len > max_addr) {
Could
you use the same consitions also in responder code?
In file src/responder/nss/nsssrv_mmap_cache.c, there is a similar code.
# rec = MC_SLOT_TO_PTR(mcc->data_table, slot, struct sss_mc_rec);
# name_ptr = *((rel_ptr_t *)rec->data);
# /* FIXME: This check relies on fact that offset of member strs
# * is the same in structures sss_mc_pwd_data and sss_mc_group_data. */
# if (name_ptr != offsetof(struct sss_mc_pwd_data, strs)) {
# DEBUG(SSSDBG_FATAL_FAILURE,
# ("Corrupted fastcache. name_ptr value is %u.\n", name_ptr));
And it was one of simo's objections in previous mail and FIXME will be removed.
+ ret = ENOENT;
+ goto done;
+ }
From 9688783586aae89bf7da5923fd7a7de8b6f6694d Mon Sep 17 00:00:00
2001
From: Michal Zidek <mzidek(a)redhat.com>
Date: Wed, 14 Aug 2013 18:01:30 +0200
Subject: [PATCH 2/3] mmap_cache: Remove triple checks in client code.
ACK
From 5db081330768957218d8d372c5ccf8dc75f223d7 Mon Sep 17 00:00:00
2001
From: Michal Zidek <mzidek(a)redhat.com>
Date: Wed, 14 Aug 2013 18:22:06 +0200
Subject: [PATCH 3/3] mmap_cache: Of by one error.
Removes off by one error when using macro MC_SIZE_TO_SLOTS
and adds new macro MC_SLOT_WITHIN_BOUNDS.
---
src/responder/nss/nsssrv_mmap_cache.c | 12 ++++++------
src/sss_client/nss_mc_group.c | 8 ++++----
src/sss_client/nss_mc_passwd.c | 8 ++++----
src/util/mmap_cache.h | 3 +++
4 files changed, 17 insertions(+), 14 deletions(-)
+++ b/src/util/mmap_cache.h
@@ -67,6 +67,9 @@ typedef uint32_t rel_ptr_t;
#define MC_SLOT_TO_PTR(base, slot, type) \
(type *)((base) + ((slot) * MC_SLOT_SIZE))
+#define MC_SLOT_WITHIN_BOUNDS(slot, dt_size) \
+ ((slot) <= ((dt_size) / MC_SLOT_SIZE))
^^^^
This is wrong. I tested edge case "slot == ((dt_size) / MC_SLOT_SIZE)"
with gdb cheating
and record was exactly behind the data_table, but on the other side
I succesfully tested patch "Store corrupted mmap cache before reset"
and backup file passwd_corrupted was created without any problem.
+
#define MC_VALID_BARRIER(val) (((val) & 0xff000000) == 0xf0000000)
#define MC_CHECK_RECORD_LENGTH(mc_ctx, rec) \
--
1.7.11.2
LS