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Tue, 27 Oct 2026 11:56:01 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id e7lhLlGR4GohaQAAD6G6ig (envelope-from ); Tue, 27 Oct 2026 11:56:01 +0000 Message-ID: <5fd819c3-9c6e-4273-a340-4ca190573cd7@suse.de> Date: Tue, 27 Oct 2026 12:54:48 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net v2 2/5] ipv4: fix shift-out-of-bounds in ip_rt_send_redirect() To: Jiayuan Chen , netdev@vger.kernel.org Cc: stable@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Randy Dunlap , David Ahern , Ido Schimmel , Thomas Gleixner , Joel Granados , Petr Pavlu , Kuniyuki Iwashima , Willem de Bruijn , Maoyi Xie , Daniel J Blueman , Jiri Wiesner , Gerd Rausch , Oleg Nesterov , Chia-Yu Chang , Wyatt Feng , Yung Chih Su , Hannes Frederic Sowa , Flavio Leitner , Petr Mladek , "Paul E. McKenney" , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261027104701.296240-1-jiayuan.chen@linux.dev> <20261027104701.296240-3-jiayuan.chen@linux.dev> Content-Language: en-US From: Fernando Fernandez Mancera In-Reply-To: <20261027104701.296240-3-jiayuan.chen@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-13.29 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; RCPT_COUNT_TWELVE(0.00)[32]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com,icloud.com]; R_RATELIMIT(0.00)[to_ip_from(RLrr9ek4ud4f4qwi71m7motjzt)]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[vger.kernel.org,davemloft.net,kernel.org,redhat.com,lwn.net,linuxfoundation.org,infradead.org,nvidia.com,suse.com,google.com,ntu.edu.sg,quora.org,suse.de,oracle.com,nokia-bell-labs.com,icloud.com,gmail.com,stressinduktion.org]; MID_RHS_MATCH_FROM(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,imap1.dmz-prg2.suse.org:helo,linux.dev:email] X-Spam-Score: -13.29 X-Spam-Level: X-Spam-Flag: NO On 10/27/26 11:45 AM, Jiayuan Chen wrote: > ip_rt_redirect_number is the max number of ICMP Redirects we send to one > endpoint; once we hit it we stop. Before that, ip_rt_redirect_load gives > the redirects an exponential backoff: > > if (peer->n_redirects == 0 || > time_after(jiffies, > (peer->rate_last + > (ip_rt_redirect_load << peer->n_redirects)))) { > > n_redirects grows until it reaches ip_rt_redirect_number, and both > redirect_number and redirect_load are plain proc_dointvec sysctls with > no upper bound. Set redirect_number past 32 and n_redirects climbs past > 31, so "ip_rt_redirect_load << peer->n_redirects" shifts a 32-bit int by >> = 32 bits, which is UB: > > UBSAN: shift-out-of-bounds in net/ipv4/route.c:949:6 > shift exponent 32 is too large for 32-bit type 'int' > CPU: 1 UID: 0 PID: 1845 Comm: ping Not tainted 7.3.0-rc7+ #364 PREEMPT > Call Trace: > > dump_stack_lvl+0xc1/0xf0 > dump_stack+0x10/0x20 > __ubsan_handle_shift_out_of_bounds+0x1d1/0x390 > ip_rt_send_redirect.cold+0x2c/0x146 > ip_forward+0x1ddc/0x2430 > ip_rcv+0x2b1/0x320 > __netif_receive_skb_one_core+0x16b/0x1c0 > __netif_receive_skb+0x21/0x150 > process_backlog+0x37e/0x1200 > __napi_poll.constprop.0+0xa5/0x5e0 > net_rx_action+0x4c0/0xf70 > > Bounding redirect_number instead is not an option: 0 disables redirects > and -1 removes the cap. Compute the backoff in u64 with the shift count > capped at 31, which cannot overflow once ip_rt_redirect_load is > non-negative, and clamp the result to MAX_JIFFY_OFFSET: on 32-bit a > backoff of 2^31 or more is read by time_after() as already expired. This > keeps redirect_number as the limit on how many ICMP redirects are sent, > and the shift can no longer go out of bounds. > > redirect_load on the other hand gets a lower bound of 0. A negative > backoff never meant anything, the old code only happened to treat it as > no backoff, and once converted to u64 it would turn into the maximum > backoff instead. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: stable@vger.kernel.org > Signed-off-by: Jiayuan Chen Reviewed-by: Fernando Fernandez Mancera Thanks!