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

Jakub Hrozek jhrozek at redhat.com
Mon Sep 23 09:37:39 UTC 2013


On Mon, Sep 23, 2013 at 10:57:55AM +0200, Lukas Slebodnik wrote:
> On (22/09/13 17:47), Jakub Hrozek wrote:
> >On Tue, Sep 17, 2013 at 07:27:17PM +0200, Michal Židek wrote:
> >> On 09/17/2013 07:09 PM, 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 do not have strong opinion on this, so I am fine either way.
> >> 
> >> Michal
> >
> >Before pushing the patches, I have two questions:
> >
> >1) Do these patches cover the same error as the ones Lukas has on the
> >list now?
> >
> >2) About this change:
> >diff --git a/src/sss_client/nss_mc_common.c b/src/sss_client/nss_mc_common.c
> >index a0a70ab..6764d80 100644
> >--- a/src/sss_client/nss_mc_common.c
> >+++ b/src/sss_client/nss_mc_common.c
> >@@ -190,6 +190,10 @@ errno_t sss_nss_mc_get_record(struct sss_cli_mc_ctx *ctx,
> >     int count;
> >     int ret;
> >
> >+    if (!MC_SLOT_WITHIN_BOUNDS(slot, ctx->dt_size)) {
> >+        return EINVAL;
> >+    }
> >+     
> >     /* try max 5 times */
> >     for (count = 5; count > 0; count--) {
> >         rec = MC_SLOT_TO_PTR(ctx->data_table, slot, struct sss_mc_rec);
> >
> >All paths that call sss_nss_mc_get_record() also check for
> >MC_SLOT_WITHIN_BOUNDS. Does it make sense to check both?
> 
> I have never hit crash in client code, while I was testing mmap_cache.
> I might be caused by later synchronization memory with mmaped file.
> In theory, sss_client should be first who access to corrupted cache.
> It is better to be "bulletproof" in client code.
> 
> If you want to push this patch also to master, there will be
> (lots of) conflicts, because each version try to fix bug in different way.
> 
> LS

OK, let's go with pushing Michal's patch to sssd-1-9, sssd-1-10 and
sssd-1-11 and yours to master.




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