[SSSD] [PATCH] Check slot validity before MC_SLOT_TO_PTR.

Michal Židek mzidek at redhat.com
Tue Sep 17 16:33:47 UTC 2013


On 09/17/2013 06:15 PM, Lukas Slebodnik wrote:
> On (17/09/13 17:15), Michal Židek wrote:
>> On 09/17/2013 04:41 PM, Lukas Slebodnik wrote:
>>> On (16/09/13 18:16), Michal Židek wrote:
>>>> On 09/14/2013 12:35 AM, Lukas Slebodnik wrote:
>>>>> On (13/09/13 19:17), Michal Židek wrote:
>>>>>> On 09/13/2013 05:58 PM, Michal Židek wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> This patch should add another line of defence against memory cache
>>>>>>> problems caused by accessing slot outside of bounds.
>>>>>>>
>>>>>>> Thanks
>>>>>>> Michal
>>>>>>>
>>>>>>
>>>>>> After discussion with Lukas I am attaching alternative version
>>>>>> without the call to save the corrupted cache.
>>>>>>
>>>>>> Thanks
>>>>>> Michal
>>>>>>
>>>>>
>>>>> I tested patch with latest sssd-1-9 on RHEL6.
>>>>>
>>>>> Message was written to the sssd_nss.log:
>>>>> (Sat Sep 14 00:19:24 2013) [sssd[nss]] [sss_mc_get_next_slot_with_hash]
>>>>> (0x0010): Corrupted fastcache. Slot number too big.
>>>>>
>>>>> But it seems that sssd_nss crashed.
>>>>>
>>>>> Program received signal SIGILL, Illegal instruction.
>>>>> 0x00007fa63f8b5b03 in mabort () from /lib64/libc.so.6
>>>>> #0  0x00007fa63f8b5b03 in mabort () from /lib64/libc.so.6
>>>>> No symbol table info available.
>>>>> #1  0x0000000000000008 in ?? ()
>>>>> No symbol table info available.
>>>>> #2  0x0000000001086cf0 in ?? ()
>>>>> No symbol table info available.
>>>>> #3  0x00000000010842a0 in ?? ()
>>>>> No symbol table info available.
>>>>> #4  0x00000000004288de in sss_mc_find_free_slots (_mcc=0x1086cf0, rec_len=252, key=<value optimized out>, _rec=0x7fff1b6bb008) at src/responder/nss/nsssrv_mmap_cache.c:495
>>>>>          tot_slots = <value optimized out>
>>>>>          i = <value optimized out>
>>>>>          rec = <value optimized out>
>>>>>          cur = 0
>>>>>          t = <value optimized out>
>>>>>          used = true
>>>>> #5  sss_mc_get_record (_mcc=0x1086cf0, rec_len=252, key=<value optimized out>, _rec=0x7fff1b6bb008) at src/responder/nss/nsssrv_mmap_cache.c:637
>>>>>          mcc = 0x7fa632dfa038
>>>>>          old_rec = <value optimized out>
>>>>>          rec = <value optimized out>
>>>>>          old_slots = <value optimized out>
>>>>>          num_slots = 8
>>>>>          base_slot = <value optimized out>
>>>>>          ret = 853516376
>>>>>          i = <value optimized out>
>>>>>          __FUNCTION__ = "sss_mc_get_record"
>>>>> #6  0x0000000000428eee in sss_mmap_cache_pw_store (_mcc=0x10842a0, name=0x7fff1b6bb140, pw=0x7fff1b6bb150, uid=126516, gid=16000, gecos=0x7fff1b6bb180, homedir=0x7fff1b6bb170, shell=0x7fff1b6bb160) at src/responder/nss/nsssrv_mmap_cache.c:731
>>>>>          mcc = 0x1086cf0
>>>>>          rec = <value optimized out>
>>>>>          data = <value optimized out>
>>>>>          uidkey = {str = 0x7fff1b6bb010 "126516", len = 7}
>>>>>          uidstr = "126516\000\000\021)\213"
>>>>>          data_len = 204
>>>>>          rec_len = 252
>>>>>          pos = <value optimized out>
>>>>>          ret = <value optimized out>
>>>>>
>>>>> LS
>>>>>
>>> The crash was caused, because mmap_cache was invalidated
>>> and memset was called for invalidated record.
>>>
>>> memset(rec->data, MC_INVALID_VAL8, <snip> * MC_SIZE_TO_SLOTS(rec->len))
>>>                                                              ^^^^^^^^^^
>>>                                                      rec->len is 0xffffffff
>>>>
>>>> Good catch.
>>>>
>>>> In function sss_mc_get_next_slot_with_hash I returned MC_INVALID_VAL
>>>> in case of failure. This function is called in function
>>>> sss_mc_rm_rec_from_chain, which returns no error code. So the upper
>>>> layers worked with the wrong MC_INVALID_VAL, as if it was valid value
>>>> and the MC_PTR_TO_SLOT resulted in some big slot number (which
>>>> probably caused the crash). In this patch I populate the information
>>>> about failure to to sss_mc_invalidate_rec and terminate it if
>>>> necessary.
>>>>
>>>> New patch is attached. Please run the testing script with your
>>>> configuration that failed to see if it is fixed.
>>>>
>>>> Thanks
>>>> Michal
>>>>
>>> I ran a stress test for 20+ hours and sssd_nss didn't crash,
>>> only mmap_cache was reseted or reinvalidated.
>>>
>>> Here is sssd_nss.log:
>>> =============================================================
>>> (Mon Sep 16 18:49:56 2013) [sssd[nss]] [monitor_common_rotate_logs] (0x0010): Debug level changed to 0x0070
>>> (Mon Sep 16 18:49:57 2013) [sssd[nss]] [monitor_common_rotate_logs] (0x0010): Debug level changed to 0x0030
>>> (Mon Sep 16 18:53:31 2013) [sssd[nss]] [setpwent_result_timeout] (0x0020): setpwent result object has expired. Cleaning up.
>>> (Mon Sep 16 19:37:17 2013) [sssd[nss]] [sss_mc_find_record] (0x0010): Corrupted fastcache. name_ptr value is 16.
>>> --- 1st reset.
>>> (Mon Sep 16 21:32:40 2013) [sssd[nss]] [sss_mc_get_next_slot_with_hash] (0x0010): Corrupted fastcache. Slot number too big.
>>> --- 2nd reset.
>>> (Mon Sep 16 22:04:04 2013) [sssd[nss]] [sss_mc_find_record] (0x0010): Corrupted fastcache. name_ptr value is 909128497.
>>> --- 3rd reset.
>>> (Mon Sep 16 23:15:23 2013) [sssd[nss]] [sss_mc_get_next_slot_with_hash] (0x0010): Corrupted fastcache. Slot number too big.
>>> (Mon Sep 16 23:40:19 2013) [sssd[nss]] [sss_mc_is_valid_rec] (0x0010): Corrupted fastcache. Slot number too big.
>>> (Mon Sep 16 23:40:19 2013) [sssd[nss]] [sss_mc_get_record] (0x0020): Fatal internal mmap cache error, invalidating cache!
>>> (Mon Sep 16 23:40:19 2013) [sssd[nss]] [fill_pwent] (0x0020): Failed to store user testbigldap129485(default) in mmap cache!
>>> --- 1st invalidation.
>>> (Tue Sep 17 06:06:51 2013) [sssd[nss]] [sss_mc_get_next_slot_with_hash] (0x0010): Corrupted fastcache. Slot number too big.
>>> --- 4th reset.
>>> (Tue Sep 17 06:25:04 2013) [sssd[nss]] [sss_mc_add_rec_to_chain] (0x0010): Corrupted fastcache. Slot number too big.
>>> --- 5th reset.
>>> (Tue Sep 17 07:48:23 2013) [sssd[nss]] [sss_mc_get_next_slot_with_hash] (0x0010): Corrupted fastcache. Slot number too big.
>>> --- 6th reset.
>>> (Tue Sep 17 08:08:36 2013) [sssd[nss]] [sss_mc_is_valid_rec] (0x0010): Corrupted fastcache. Slot number too big.
>>> (Tue Sep 17 08:08:36 2013) [sssd[nss]] [sss_mc_get_record] (0x0020): Fatal internal mmap cache error, invalidating cache!
>>> (Tue Sep 17 08:08:36 2013) [sssd[nss]] [fill_pwent] (0x0020): Failed to store user testbigldap119808(default) in mmap cache!
>>> --- 2nd invalidation.
>>> (Tue Sep 17 12:56:02 2013) [sssd[nss]] [sss_mc_get_next_slot_with_hash] (0x0010): Corrupted fastcache. Slot number too big.
>>> --- 7th reset.
>>> (Tue Sep 17 13:22:27 2013) [sssd[nss]] [sss_mc_is_valid_rec] (0x0010): Corrupted fastcache. Slot number too big.
>>> (Tue Sep 17 13:22:27 2013) [sssd[nss]] [sss_mc_get_record] (0x0020): Fatal internal mmap cache error, invalidating cache!
>>> (Tue Sep 17 13:22:27 2013) [sssd[nss]] [fill_pwent] (0x0020): Failed to store user testbigldap126987(default) in mmap cache!
>>> --- 3rd invalidation.
>>> (Tue Sep 17 14:30:56 2013) [sssd[nss]] [sss_mc_get_next_slot_with_hash] (0x0010): Corrupted fastcache. Slot number too big.
>>> --- 8th reset.
>>> (Tue Sep 17 14:54:21 2013) [sssd[nss]] [sss_mc_add_rec_to_chain] (0x0010): Corrupted fastcache. Slot number too big.
>>> --- 9th reset.
>>> =============================================================
>>>
>>> In older log sile, I also saw reseting caches in another functions.
>>> BTW: I tested my patch with "two next pointers" and it did not crash and
>>> log file is empty :-)
>>>
>>> just few small nitpicks.
>>>
>>> >From ba054788692f713eed0738f5b3f5e6bb48fe4c4b Mon Sep 17 00:00:00 2001
>>>> From: Michal Zidek <mzidek at redhat.com>
>>>> Date: Fri, 13 Sep 2013 17:41:28 +0200
>>>> Subject: [PATCH] Check slot validity before MC_SLOT_TO_PTR.
>>>>
>>>> resolves:
>>>> https://fedorahosted.org/sssd/ticket/2049
>>>> ---
>>>> src/responder/nss/nsssrv_mmap_cache.c | 80 +++++++++++++++++++++++++++++++----
>>>> src/sss_client/nss_mc_common.c        |  4 ++
>>>> 2 files changed, 75 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/src/responder/nss/nsssrv_mmap_cache.c b/src/responder/nss/nsssrv_mmap_cache.c
>>>> index 4e45405..09a4c2b 100644
>>>> --- a/src/responder/nss/nsssrv_mmap_cache.c
>>>> +++ b/src/responder/nss/nsssrv_mmap_cache.c
>>>> @@ -191,6 +191,13 @@ static void sss_mc_add_rec_to_chain(struct sss_mc_ctx *mcc,
>>>>      }
>>>>
>>>>      do {
>>>> +        if (!MC_SLOT_WITHIN_BOUNDS(slot, mcc->dt_size)) {
>>>> +            DEBUG(SSSDBG_FATAL_FAILURE,
>>>> +                  ("Corrupted fastcache. Slot number too big.\n"));
>>>> +            sss_mmap_cache_reset(mcc);
>>>> +            return;
>>>> +        }
>>>> +
>>>>          cur = MC_SLOT_TO_PTR(mcc->data_table, slot, struct sss_mc_rec);
>>>>          if (cur == rec) {
>>>>              /* rec already stored in hash chain */
>>>> @@ -205,16 +212,24 @@ static void sss_mc_add_rec_to_chain(struct sss_mc_ctx *mcc,
>>>>      cur->next = MC_PTR_TO_SLOT(mcc->data_table, rec);
>>>> }
>>>>
>>>> -static inline uint32_t
>>>> +static inline errno_t
>>>> sss_mc_get_next_slot_with_hash(struct sss_mc_ctx *mcc,
>>>>                                 struct sss_mc_rec *start_rec,
>>>> -                               uint32_t hash)
>>>> +                               uint32_t hash,
>>>> +                               uint32_t *_slot)
>>>> {
>>>>      struct sss_mc_rec *rec;
>>>>      uint32_t slot;
>>>>
>>>>      slot = start_rec->next;
>>>>      while (slot != MC_INVALID_VAL) {
>>>> +        if (!MC_SLOT_WITHIN_BOUNDS(slot, mcc->dt_size)) {
>>>> +            DEBUG(SSSDBG_FATAL_FAILURE,
>>>> +                  ("Corrupted fastcache. Slot number too big.\n"));
>>>> +            sss_mmap_cache_reset(mcc);
>>>> +            return EINVAL;
>>>> +        }
>>>> +
>>>>          rec = MC_SLOT_TO_PTR(mcc->data_table, slot, struct sss_mc_rec);
>>>>          if (rec->hash1 == hash || rec->hash2 == hash) {
>>>>              break;
>>>> @@ -223,23 +238,26 @@ sss_mc_get_next_slot_with_hash(struct sss_mc_ctx *mcc,
>>>>          slot = rec->next;
>>>>      }
>>>>
>>>> -    return slot;
>>>> +    *_slot = slot;
>>>> +
>>>> +    return EOK;
>>>> }
>>>>
>>>> -static void sss_mc_rm_rec_from_chain(struct sss_mc_ctx *mcc,
>>>> +static errno_t sss_mc_rm_rec_from_chain(struct sss_mc_ctx *mcc,
>>>>                                       struct sss_mc_rec *rec,
>>>>                                       uint32_t hash)
>>>> {
>>>>      struct sss_mc_rec *prev = NULL;
>>>>      struct sss_mc_rec *cur = NULL;
>>>>      uint32_t slot;
>>>> +    uint32_t ret;
>>>>
>>>>      if (hash > MC_HT_ELEMS(mcc->ht_size)) {
>>>>          /* It can happen if rec->hash1 and rec->hash2 was the same.
>>>>           * or it is invalid hash. It is better to return
>>>>           * than trying to access out of bounds memory
>>>>           */
>>>> -        return;
>>>> +        return EOK;
>>>                   ^^^
>>>            EOK should be returned on if hash is equal to MC_INVALID_VAL
>>
>> Ok. I also changed the comments (split the error and normal case).
>>
>>>
>>>>      }
>>>>
>>>>      slot = mcc->hash_table[hash];
>>>> @@ -247,18 +265,37 @@ static void sss_mc_rm_rec_from_chain(struct sss_mc_ctx *mcc,
>>>>          /* record has already been removed. It may happen if rec->hash1 and
>>>>           * rec->has2 are the same. (It is not very likely).
>>>>           */
>>>> -        return;
>>>> +        return EOK;
>>>> +    }
>>>> +
>>>> +    if (!MC_SLOT_WITHIN_BOUNDS(slot, mcc->dt_size)) {
>>>> +        DEBUG(SSSDBG_FATAL_FAILURE,
>>>> +              ("Corrupted fastcache. Slot number too big.\n"));
>>>> +        sss_mmap_cache_reset(mcc);
>>>> +        return EINVAL;
>>>>      }
>>>> +
>>>>      cur = MC_SLOT_TO_PTR(mcc->data_table, slot, struct sss_mc_rec);
>>>>      if (cur == rec) {
>>>>          /* rec->next can refer to record without matching hashes.
>>>>           * We need to skip this(those) records, because
>>>>           * mcc->hash_table[hash] have to refer to valid start of the chain.
>>>>           */
>>>> -        mcc->hash_table[hash] = sss_mc_get_next_slot_with_hash(mcc, rec, hash);
>>>> +        ret = sss_mc_get_next_slot_with_hash(mcc, rec, hash,
>>>> +                                             &mcc->hash_table[hash]);
>>>> +        if (ret != EOK) {
>>>> +            return ret;
>>>> +        }
>>> This condition does not make sense.
>>> You can use:
>>>        either return ret;
>>>        or return sss_mc_get_next_slot_with_hash
>>
>> Well, I wanted the function to run to the end if nothing went wrong,
>> but yes, in this case we return at several places in the function so
>> it does not make much sense.
>>
>>>
>>> LS
>>
>> Thanks for the review Lukas. New patch is attached.
>>
>> Michal
>
> I tested patch for sssd-1-9 branch on RHEL6
> and it works fine. I think it is good alternative for sssd-1-9 branch.
>
> ACK
>
> LS

I would personally prefer to have this in master as well, even if the 
currently known issues will be fixed with your patch ([PATCH] 
mmap_cache: Use two chains for hash collision). I think it hurts nothing 
to be more defensive.

Michal




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