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>
next in thread | raw e-mail | index | archive | help
>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:
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200501181438.j0IEceum023351>