[kamailio/kamailio] dispatcher algorithm 11 with congestion control memory corruption problem (#1649)
21 Sep
2018
21 Sep
'18
7 p.m.
### Description
Segfault , suspected cause, writing out of bound of an array
### Troubleshooting
In progress
#### Reproduction
Hard
#### Debugging Data
```
/* code reference */
typedef struct _ds_set {
int id; /*!< id of dst set */
int nr; /*!< number of items in dst set */
int last; /*!< last used item in dst set (round robin) */
int wlast; /*!< last used item in dst set (by weight) */
int rwlast; /*!< last used item in dst set (by relative weight) */
ds_dest_t *dlist;
unsigned int wlist[100];
unsigned int rwlist[100];
struct _ds_set *next[2];
int longer;
gen_lock_t lock;
} ds_set_t;
Here we can see that next is having invalid value (in fact it should have been 0/NULL in
this case) : 20000000220000000220
2964>->-->--ds_ping_set(node->next[i]);
(gdb) bt
#0 0x00007f3b1cfde6c7 in ds_ping_set (node=0x200000002) at dispatch.c:2964
#1 0x00007f3b1cfde6d3 in ds_ping_set (node=0x7f3a99a09fc8) at dispatch.c:2964
#2 0x00007f3b1cfde6d3 in ds_ping_set (node=0x7f3a99a09828) at dispatch.c:2964
#3 0x00007f3b1cfdf9ad in ds_check_timer (ticks=9987101, param=0x0) at dispatch.c:3022
#4 0x00005644376a3652 in sr_wtimer_exec (ticks=9987101, param=0x0) at
core/timer_proc.c:390
#5 0x00005644376a276d in fork_sync_timer (child_id=-1, desc=0x5644378904c1
"secondary timer", make_sock=1, f=0x5644376a330c <sr_wtimer_exec>,
param=0x0, interval=1000) at core/timer_proc.c:224
#6 0x00005644376a39ca in sr_wtimer_start () at core/timer_proc.c:416
#7 0x00005644374d2d59 in main_loop () at main.c:1702
#8 0x00005644374da171 in main (argc=12, argv=0x7ffe7c214ac8) at main.c:2650
(gdb) p (ds_set_t) *0x7f3a99a09828
$1 = {id = 2, nr = 2, last = 0, wlast = 0, rwlast = 0, dlist = 0x7f3a99a0aab8, wlist = {0
<repeats 100 times>}, rwlist = {0 <repeats 100 times>}, next =
{0x7f3a99a09fc8, 0x0}, longer = 0, lock = {val = 0}}
(gdb) p (ds_set_t) *0x0x7f3a99a09fc8
Invalid number "0x0x7f3a99a09fc8".
(gdb) p (ds_set_t) *0x7f3a99a09fc8
$2 = {id = 1, nr = 3, last = 0, wlast = 0, rwlast = 0, dlist = 0x7f3a99a0a7f8, wlist = {1,
0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 1,
1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0,
1,~
1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0,
0, 0, 1, 1, 0, 0, 0, 1, 1}, rwlist = {1, 1, 2, 2, 1, 0, 1, 0, 2, 2, 0, 0, 1, 0, 1, 0, 0,
0, 1, 0, 0, 0, 1, 2, 0, 1, 2, 1, 0, 0, 0, 0, 2, 1, 0, 2, 1, 2, 1, 1, 0, 2, 1, 2, 2, 2, 0,
0,~
2, 0, 2, 2, 0, 2, 2, 0, 1, 2, 1, 1, 2, 1, 1, 0, 1, 1, 0, 1, 0, 2, 2, 2, 2, 2, 0, 0, 2,
0, 1, 0, 2, 1, 1, 2, 0, 2, 1, 2, 1, 1, 0, 2, 1, 2, 2, 1, 2, 1, 1, 0}, next = {0x200000002,
0x200000002}, longer = 2, lock = {val = 0}}
(gdb)
```
### Possible Solutions
Further analysis of the relevant source code
around dp_init_relative_weights()
and the way it was reused with congestion control.
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21 Sep
21 Sep
7:41 p.m.
more precisely, looks like 5 x ints with value 2 where written out of bound
2,1,2,1,1,0
2 1 2 1 1 0 222220
overflow
```
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*1)
$53 = 0
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*2)
$54 = 2
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*3)
$55 = 2
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*4)
$56 = 2
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*5)
$57 = 2
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*6)
$58 = 2
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*7)
$59 = 0
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*8)
$60 = 1
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*9)
$61 = 1
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*10)
$62 = 2
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*11)
$63 = 1
(gdb) p (int)*(0x7f3a99a09fc8 + sizeof(struct _ds_set) - sizeof(unsigned int)*12)
$64 = 2
```
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8:18 p.m.
The lock was set to 0 else it would have been 48 times 2
```
/* if the array was not completely filled (i.e., the sum of rweights is
* less than 100 due to truncated), then use last address to fill the rest */
unsigned int last_insert =
t > 0 ? dset->rwlist[t - 1] : (unsigned int)(dset->nr - 1);
for(j = t; j < 100; j++)
dset->rwlist[j] = last_insert;
/* shuffle the content of the array in order to mix the selection
* of the addresses (e.g., if first address has weight=20, avoid
* sending first 20 calls to it, but ensure that within a 100 calls,
* 20 go to first address */
shuffle_uint100array(dset->rwlist);
lock_release(&dset->lock);
return 0;
}
```
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9:16 p.m.
Re run the code in isolation using the inputs present
```
~/git/examples$ valgrind ./bin/shuffle
==5245== Memcheck, a memory error detector
==5245== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==5245== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==5245== Command: ./bin/shuffle
==5245==
rw_sum[0][143][33]
rw_sum[1][143][33]
rw_sum[2][143][32]
redistributed array
0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|0|0|
fill the truncate t[98] with[2]
0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|
shuffled array
2|2|2|1|1|0|1|1|2|1|1|0|0|0|2|1|2|1|1|2|1|0|2|2|1|0|0|0|1|0|2|2|1|0|0|2|2|2|0|1|0|2|0|1|2|0|2|2|1|0|2|0|0|1|1|0|2|1|2|1|0|2|1|2|1|2|1|2|0|0|2|1|0|0|2|1|2|0|0|2|1|0|0|2|1|1|1|1|2|0|1|1|1|2|0|2|0|0|2|0|
==5245==
==5245== HEAP SUMMARY:
==5245== in use at exit: 0 bytes in 0 blocks
==5245== total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==5245==
==5245== All heap blocks were freed -- no leaks are possible
==5245==
==5245== For counts of detected and suppressed errors, rerun with: -v
==5245== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
```
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9:56 p.m.
shuffle_uint100array looks good, seems like the corruption took place before the lock was
released since the int was set back to 0, hmm, still thinking ...
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10:12 p.m.
quite sure I found it !
```
/**
* Initialize the relative weight distribution for a destination set
* - fill the array of 0..99 elements where to keep the index of the
* destination address to be used. The Nth call will use
* the address with the index at possition N%100
*/
int dp_init_relative_weights(ds_set_t *dset)
{
int j;
int k;
int t;
if(dset == NULL || dset->dlist == NULL)
return -1;
lock_get(&dset->lock);
int rw_sum = 0;
/* find the sum of relative weights*/
for(j = 0; j < dset->nr; j++) { // READING THE FLAG ONCE
if(ds_skip_dst(dset->dlist[j].flags))
continue;
rw_sum += dset->dlist[j].attrs.rweight;
}
if(rw_sum == 0) {
lock_release(&dset->lock);
return 0;
}
/* fill the array based on the relative weight of each destination */
t = 0;
for(j = 0; j < dset->nr; j++) {
if(ds_skip_dst(dset->dlist[j].flags)) // READING THE FLAG AGAIN, SEGFAULT IF THEY
CHANGED !
continue;
int current_slice =
dset->dlist[j].attrs.rweight * 100 / rw_sum; //truncate here;
LM_DBG("rw_sum[%d][%d][%d]\n",j, rw_sum, current_slice);
for(k = 0; k < current_slice; k++) {
dset->rwlist[t] = (unsigned int)j;
t++;
}
}
/* if the array was not completely filled (i.e., the sum of rweights is
* less than 100 due to truncated), then use last address to fill the rest */
unsigned int last_insert =
t > 0 ? dset->rwlist[t - 1] : (unsigned int)(dset->nr - 1);
for(j = t; j < 100; j++)
dset->rwlist[j] = last_insert;
/* shuffle the content of the array in order to mix the selection
* of the addresses (e.g., if first address has weight=20, avoid
* sending first 20 calls to it, but ensure that within a 100 calls,
* 20 go to first address */
shuffle_uint100array(dset->rwlist);
lock_release(&dset->lock);
return 0;
}
```
```
rw_sum[0][96][50]
rw_sum[1][96][50]
rw_sum[2][96][48]
redistributed array
0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|
fill the truncate t[148] with[2]
0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|
shuffled array
1|0|1|1|0|0|0|1|1|1|1|1|1|1|0|1|1|0|1|0|0|1|0|0|0|0|0|0|1|1|1|1|1|1|1|0|0|1|1|0|0|1|1|0|0|1|0|0|0|1|1|0|1|0|0|0|1|1|0|0|1|0|0|1|0|1|0|1|0|0|1|0|0|1|0|1|0|0|1|0|0|1|0|1|0|1|1|1|1|1|0|0|1|0|1|1|1|0|0|0|
*** stack smashing detected ***: ./bin/shuffle terminated
Aborted
```
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10:12 p.m.
Syncronization problem where we read a value twice that could change in between.
I even found 48 offset in this case !
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24 Sep
24 Sep
10:31 a.m.
I guess you are going to make a pull request from your cloned repository with the patches
referred above.
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25 Sep
25 Sep
2:10 p.m.
Closed #1649.
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2254
days inactive
2258
days old
8 comments
2 participants
participants (2)
-
Daniel-Constantin Mierla -
Julien Chavanton