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Date: Sat, 28 Dec 2013 01:28:42 +0000 (UTC)
From: David Wuertele <dave+gmane@...rtele.com>
To: musl@...ts.openwall.com
Subject: Re: NULL deref SEGV in malloc.c:unbin()
I wrote:
> Rich Felker <dalias <at> aerifal.cx> writes:
> > On Fri, Dec 27, 2013 at 07:44:23PM +0000, David Wuertele wrote:
> > > Rich Felker <dalias <at> aerifal.cx> writes:
> > > > On Fri, Dec 27, 2013 at 06:35:00PM +0000, David Wuertele wrote:
> > > > > I wonder if anyone has hit this before? In unbin(),
> > > > > c->next->prev is set, but c->next is NULL. It happens
> > > > > repeatedly, and here's what gdb says:
> > > > >
> > > >
> > > > It's almost surely a case of memory corruption by the calling
> > > > program, most likely using memory after it's already been
> > > > freed.
> > >
> > > Hmm, my program calls malloc() once and never calls free().
> >
> > And this crash happens on the very first call to malloc? Or did you
> > mean it only called it once successfully?
> >
>
> Now I am watching all memory locations that mal.bins[40].head points
> to in its history, but the going is very slow.
I removed all my calls to malloc(), now it is only musl that is
calling it. I'm watching everything that I think might be related.
It looks like calloc(), opendir(), or free() are the culprit.
(gdb) info watch
Num Type Disp Enb Address What
2 watchpoint keep y mal.bins[40].head
breakpoint already hit 2 times
print *mal.bins[40].head
bt
cont
3 watchpoint keep y mal.bins[40].head.next
breakpoint already hit 47 times
print *mal.bins[40].head
bt
cont
3.1 y mal.bins[40].head.next
3.2 y mal.bins[40].head.next
4 watchpoint keep y mal.bins[40].head.prev
breakpoint already hit 32 times
print *mal.bins[40].head
bt
cont
4.1 y mal.bins[40].head.prev
4.2 y mal.bins[40].head.prev
(gdb) c
Watchpoint 4: mal.bins[40].head.prev
Old value = (struct chunk *) 0xc9690
New value = (struct chunk *) 0x0
0x0008b268 in calloc (m=519, n=2080) at src/malloc/calloc.c:20
20 in src/malloc/calloc.c
$78 = {psize = 2097, csize = 2097, next = 0x0, prev = 0x0}
#0 0x0008b268 in calloc (m=519, n=2080) at src/malloc/calloc.c:20
#1 0x00089f30 in opendir (name=0xaa8d4 ".") at src/dirent/opendir.c:19
#2 0x0000fb50 in mkchdir (path=0xbe83f89b "") at prog.c:1845
Watchpoint 3: mal.bins[40].head.next
Old value = (struct chunk *) 0x0
New value = (struct chunk *) 0x10
opendir (name=0xaa8d4 ".") at src/dirent/opendir.c:24
24 src/dirent/opendir.c: No such file or directory.
in src/dirent/opendir.c
$79 = {psize = 2097, csize = 2097, next = 0x10, prev = 0x0}
#0 opendir (name=0xaa8d4 ".") at src/dirent/opendir.c:24
#1 0x0000fb50 in mkchdir (path=0xbe83f89b "") at prog.c:1845
Watchpoint 3: mal.bins[40].head.next
Old value = (struct chunk *) 0x10
New value = (struct chunk *) 0x2139018
free (p=0x2139020) at src/malloc/malloc.c:530
530 src/malloc/malloc.c: No such file or directory.
in src/malloc/malloc.c
$80 = {psize = 2096, csize = 2097, next = 0x2139018, prev = 0x0}
#0 free (p=0x2139020) at src/malloc/malloc.c:530
#1 0x00089e84 in closedir (dir=0x2139020) at src/dirent/closedir.c:9
#2 0x0000fc80 in mkchdir (path=0xd22bc "/var/spool") at prog.c:1873
Program received signal SIGSEGV, Segmentation fault.
0x0008be70 in unbin (c=0x2139848, i=40) at src/malloc/malloc.c:241
241 in src/malloc/malloc.c
(gdb)
Dave
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