Description of problem:

n the loop for_each_string(j, tterm) of  fmt_entry function(  line:725), there  was  array out of bound write for the buffer that  led to the return address of fmt_entry function was covered later.

Version-Release number of selected component (if applicable):

<=6.0

How reproducible:

infotocap $POC

Steps to Reproduce:


The debug information is as follows:

$gdb infotocap
…
(gdb) set args $POC
 (gdb) b dump_entry.c:1143 // the stack overflow related caller point
 (gdb) r 
... 
(gdb) x/10i 
$pc => 0x41621c <dump_entry+1724>: mov %r14d,%r8d 0x41621f 
<dump_entry+1727>: mov 0x3c(%rsp),%r9d 0x416224 
<dump_entry+1732>: callq 0x410150
 <fmt_entry> 0x416229 
<dump_entry+1737>: cmpl $0x0,0x34(%rsp) ...
(gdb) si //3 times 
(gdb) i r $rsp rsp 0x7fffffffb2e8
 (gdb) x/4x $rsp 
0x7fffffffb2e8: 0x29 0x62 0x41 0x00 // the ret address
<dump_entry+1737>
 (gdb) b dump_entry.c:725
 (gdb) c //repeat 9 times 
(gdb) b dump_entry.c:724
 (gdb) c //repeat 24 times
 (gdb) b dump_entry.c:838
 (gdb) c
 Continuing. 
Breakpoint 18, fmt_entry (tterm=0x675430, pred=<optimized out>, content_only=<optimized out>, suppress_untranslatable=0, infodump=0, numbers=0) at ../progs/dump_entry.c:838
 838 len += (int) strlen(capability) + 1; 
(gdb) x/4x 0x7fffffffb2e8     //check the ret address again 
0x7fffffffb2e8: 0x2f 0x25 0x7b 0x31   //it was overflowed
(gdb) continue //until the function return 
….
Program received signal SIGSEGV, Segmentation fault. 0x00000000004135ee in fmt_entry (tterm=<optimized out>, pred=<optimized out>, content_only=<optimized out>, suppress_untranslatable=<optimized out>, infodump=<optimized out>, numbers=<optimized out>) at ../progs/dump_entry.c:984
…
 (gdb) x/10i 
$pc => 0x4135ee <fmt_entry+13470>: retq 0x4135ef 
<fmt_entry+13471>: movslq %fs:(%r14),%rax ...
 (gdb) x/4x 0x7fffffffb2e8  //check the ret address again, it was
// overflowed by  0x2f 0x25 0x7b 0x31
0x7fffffffb2e8: 0x2f 0x25 0x7b 0x31

Actual results:

specified function return address be covered
crash

Expected results:

crash

Additional info:

Credits:

This vulnerability is detected by team OWL337, with our custom fuzzer coll AFL. Please contact ganshuitao  and chaoz.cn if you need more info about the team, the tool or the vulnerability.