kern/132104: kenv buffer overflow

[Dylan Cochran]

The following reply was made to PR kern/132104; it has been noted by GNATS.

From: Dylan Cochran <a134qaed at gmail.com>
To: Jaakko Heinonen <jh at saunalahti.fi>
Cc: bug-followup at freebsd.org
Subject: Re: kern/132104: kenv buffer overflow
Date: Wed, 25 Feb 2009 16:36:32 -0500

 On Wed, Feb 25, 2009 at 1:56 PM, Jaakko Heinonen <jh at saunalahti.fi> wrote:
 >
 > Hi,
 >
 > On 2009-02-25, Dylan Cochran wrote:
 >> This prevents the panic condition, but also increases the amount of
 >> time the mutex is held. Comments?
 >>
 >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 mtx_lock(&kenv_lock);
 >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 cp =3D _getenv_dynamic(name, NULL);
 >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (cp !=3D NULL) {
 >> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 strcpy(buf, cp);
 >> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 mtx_unlock(&kenv_lock);
 >> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 len =3D strlen(buf) + 1;
 >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 len =3D strlen(cp) + 1;
 >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ret =3D malloc(len, M_KENV, =
 M_WAITOK);
 >> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 strcpy(ret, buf);
 >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 strcpy(ret, cp);
 >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 mtx_unlock(&kenv_lock);
 >
 > malloc(9) with M_WAITOK flag could sleep. You are not allowed to sleep
 > while holding a mutex.
 So if I modify it to use M_NOWAIT, I should unlock if it returns null,
 then sleep, then relock, and repeat? I'd rather not just bump up the
 *LEN values, or truncate it by adding a trailing 0 byte to the end.
 Not in 2009 anyway.
 >
 > --
 > Jaakko
 >