Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755358Ab1BNAwk (ORCPT ); Sun, 13 Feb 2011 19:52:40 -0500 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:42111 "EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755316Ab1BNAwd (ORCPT ); Sun, 13 Feb 2011 19:52:33 -0500 Date: Sun, 13 Feb 2011 16:53:09 -0800 (PST) Message-Id: <20110213.165309.123985803.davem@davemloft.net> To: jj@chaosbits.net Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, tj@kernel.org, isdn@linux-pingi.de Subject: Re: potential null pointer dereference in drivers/isdn/hisax/isdnl2.c From: David Miller In-Reply-To: References: X-Mailer: Mew version 6.3 on Emacs 23.1 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3307 Lines: 109 From: Jesper Juhl Date: Thu, 3 Feb 2011 21:27:56 +0100 (CET) > In drivers/isdn/hisax/isdnl2.c:l2_pull_iqueue() we have this: > > ... > skb = alloc_skb(oskb->len + i, GFP_ATOMIC); > memcpy(skb_put(skb, i), header, i); > ... > > If alloc_skb() fails and returns NULL then the second line will cause a > NULL pointer dereference - skb_put() gives the pointer to > skb_tail_pointer() which dereferences it. > > I'm not quite sure how this should be dealt with, so I'll just report it > rather than submit a patch. Happy bug fixing :-) Thanks Jesper, I'll fix this like so: -------------------- hisax: Fix unchecked alloc_skb() return. Jesper Juhl noticed that l2_pull_iqueue() does not check to see if alloc_skb() fails. Fix this by first trying to reallocate the headroom if necessary, rather than later after we've made hard to undo state changes. Reported-by: Jesper Juhl Signed-off-by: David S. Miller --- drivers/isdn/hisax/isdnl2.c | 35 ++++++++++++++++++++--------------- 1 files changed, 20 insertions(+), 15 deletions(-) diff --git a/drivers/isdn/hisax/isdnl2.c b/drivers/isdn/hisax/isdnl2.c index 0858791..98ac835 100644 --- a/drivers/isdn/hisax/isdnl2.c +++ b/drivers/isdn/hisax/isdnl2.c @@ -1243,14 +1243,21 @@ l2_st7_tout_203(struct FsmInst *fi, int event, void *arg) st->l2.rc = 0; } +static int l2_hdr_space_needed(struct Layer2 *l2) +{ + int len = test_bit(FLG_LAPD, &l2->flag) ? 2 : 1; + + return len + (test_bit(FLG_LAPD, &l2->flag) ? 2 : 1); +} + static void l2_pull_iqueue(struct FsmInst *fi, int event, void *arg) { struct PStack *st = fi->userdata; - struct sk_buff *skb, *oskb; + struct sk_buff *skb; struct Layer2 *l2 = &st->l2; u_char header[MAX_HEADER_LEN]; - int i; + int i, hdr_space_needed; int unsigned p1; u_long flags; @@ -1261,6 +1268,16 @@ l2_pull_iqueue(struct FsmInst *fi, int event, void *arg) if (!skb) return; + hdr_space_needed = l2_hdr_space_needed(l2); + if (hdr_space_needed > skb_headroom(skb)) { + struct sk_buff *orig_skb = skb; + + skb = skb_realloc_headroom(skb, hdr_space_needed); + if (!skb) { + dev_kfree_skb(orig_skb); + return; + } + } spin_lock_irqsave(&l2->lock, flags); if(test_bit(FLG_MOD128, &l2->flag)) p1 = (l2->vs - l2->va) % 128; @@ -1285,19 +1302,7 @@ l2_pull_iqueue(struct FsmInst *fi, int event, void *arg) l2->vs = (l2->vs + 1) % 8; } spin_unlock_irqrestore(&l2->lock, flags); - p1 = skb->data - skb->head; - if (p1 >= i) - memcpy(skb_push(skb, i), header, i); - else { - printk(KERN_WARNING - "isdl2 pull_iqueue skb header(%d/%d) too short\n", i, p1); - oskb = skb; - skb = alloc_skb(oskb->len + i, GFP_ATOMIC); - memcpy(skb_put(skb, i), header, i); - skb_copy_from_linear_data(oskb, - skb_put(skb, oskb->len), oskb->len); - dev_kfree_skb(oskb); - } + memcpy(skb_push(skb, i), header, i); st->l2.l2l1(st, PH_PULL | INDICATION, skb); test_and_clear_bit(FLG_ACK_PEND, &st->l2.flag); if (!test_and_set_bit(FLG_T200_RUN, &st->l2.flag)) { -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/