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

Jakub Hrozek jhrozek at redhat.com
Tue Sep 17 17:36:19 UTC 2013


On Tue, Sep 17, 2013 at 07:09:42PM +0200, Lukas Slebodnik wrote:
> On (17/09/13 18:33), Michal Židek wrote:
> >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.
> Your patch is not about defensive coding. The patch is about fixing corrupted
> cache in back-compatible way. In my opinion, mmap_cache source code looks much
> more complicated and readability is decreased.
> 
> LS

I don't think the readability suffers that much and maybe we can improve
it by wrapping the repeated checks in a macro?

I'm also for more defensiveness, we don't know what other strange bugs
might linger in the code.



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