Date: Tue, 18 Jan 2005 14:38:40 GMT From: Eugene Stark <stark@cs.sunysb.edu> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/76410: Null pointer dereference in net/bpf.c Message-ID: <200501181438.j0IEceum023351@www.freebsd.org> Resent-Message-ID: <200501181440.j0IEeRI5015455@freefall.freebsd.org>
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>Number: 76410
>Category: kern
>Synopsis: Null pointer dereference in net/bpf.c
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Jan 18 14:40:27 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator: Eugene Stark
>Release: 4.10-RELEASE
>Organization:
SUNY at Stony Brook
>Environment:
FreeBSD laptop.starkhome.cs.sunysb.edu 4.10-RELEASE-p4 FreeBSD 4.10-RELEASE-p4 #1: Mon Jan 17 17:51:38 EST 2005 gene@laptop.starkhome.cs.sunysb.edu:/A/src/sys/compile/LAPTOP i386
>Description:
After applying the patch I proposed in PR-76207 for a null pointer
dereference in pci/if_xl.c, I found that it exposed a different bug in
net/bpf.c. Specifically, if a call is made to bpfdetach() when no
devices have been successfully attached and consequently bpf_iflist
is NULL, then it is possible to exit the first loop in bpfdetach() with
bp == NULL, thus causing a NULL pointer dereference in the next statement.
It appears from the comments that the author wished to defend against
the case in which an attempt was made to detach a device that had never
successfully been attached. However, the code does not properly handle
the situation in which this occurs when there are no other devices that
had been attached.
>How-To-Repeat:
This occurred after applying the patch I suggest to pci/if_xl.c
in PR-76207. Although that patch avoided a crash in the xl driver proper,
the next time I saw the error it ended up taking a null pointer dereference in bpfdetach(). So to repeat the problem, one would have to
attempt to bpfdetach() a device that has not been bpfattach()ed, in a
situation in which no other devices are attached to BPF. The xl driver
will expose this problem under certain conditions.
>Fix:
I have applied the following patch to net/bpf.c:
*** bpf.c.orig Wed Dec 1 08:14:54 2004
--- bpf.c Mon Jan 17 17:51:12 2005
***************
*** 1440,1446 ****
}
/* Interface wasn't attached */
! if (bp->bif_ifp == NULL) {
splx(s);
printf("bpfdetach: %s%d was not attached\n", ifp->if_name,
ifp->if_unit);
--- 1440,1446 ----
}
/* Interface wasn't attached */
! if (bp == NULL || bp->bif_ifp == NULL) {
splx(s);
printf("bpfdetach: %s%d was not attached\n", ifp->if_name,
ifp->if_unit);
>Release-Note:
>Audit-Trail:
>Unformatted:
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