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Wed, 11 Nov 2020 09:00:08 -0800 (PST) From: Anmol Karn To: ralf@linux-mips.org, davem@davemloft.net, kuba@kernel.org Cc: saeed@kernel.org, gregkh@linuxfoundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hams@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, syzkaller-bugs@googlegroups.com, anmol.karan123@gmail.com, syzbot+a1c743815982d9496393@syzkaller.appspotmail.com Subject: [Linux-kernel-mentees] [PATCH v4 net] rose: Fix Null pointer dereference in rose_send_frame() Date: Wed, 11 Nov 2020 22:29:54 +0530 Message-Id: <20201111165954.14743-1-anmol.karan123@gmail.com> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201110194518.GA97719@Thinkpad> References: <20201110194518.GA97719@Thinkpad> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org rose_send_frame() dereferences `neigh->dev` when called from rose_transmit_clear_request(), and the first occurrence of the `neigh` is in rose_loopback_timer() as `rose_loopback_neigh`, and it is initialized in rose_add_loopback_neigh() as NULL. i.e when `rose_loopback_neigh` used in rose_loopback_timer() its `->dev` was still NULL and rose_loopback_timer() was calling rose_rx_call_request() without checking for NULL. - net/rose/rose_link.c This bug seems to get triggered in this line: rose_call = (ax25_address *)neigh->dev->dev_addr; Fix it by adding NULL checking for `rose_loopback_neigh->dev` in rose_loopback_timer(). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+a1c743815982d9496393@syzkaller.appspotmail.com Tested-by: syzbot+a1c743815982d9496393@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=9d2a7ca8c7f2e4b682c97578dfa3f236258300b3 Signed-off-by: Anmol Karn --- Changes in v4: - Free `dev`(on dev_hold()), when neigh->dev is NULL. (Suggested-by: Jakub Kicinski ) Changes in v3: - Corrected checkpatch warnings and errors (Suggested-by: Saeed Mahameed ) - Added "Fixes:" tag (Suggested-by: Saeed Mahameed ) Changes in v2: - Added NULL check in rose_loopback_timer() (Suggested-by: Greg KH ) net/rose/rose_loopback.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) -- 2.29.2 diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c index 7b094275ea8b..6a71b6947d92 100644 --- a/net/rose/rose_loopback.c +++ b/net/rose/rose_loopback.c @@ -96,10 +96,12 @@ static void rose_loopback_timer(struct timer_list *unused) } if (frametype == ROSE_CALL_REQUEST) { - if ((dev = rose_dev_get(dest)) != NULL) { + dev = rose_dev_get(dest); + if (rose_loopback_neigh->dev && dev) { if (rose_rx_call_request(skb, dev, rose_loopback_neigh, lci_o) == 0) kfree_skb(skb); } else { + dev_put(dev); kfree_skb(skb); } } else {