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Tue, 21 Apr 2026 01:54:20 -0700 (PDT) Message-ID: <9ce273bd-6912-4442-8672-4c89bebf32ed@gmail.com> Date: Tue, 21 Apr 2026 11:54:19 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] netdevsim: Initialize all fields of ip header when building dummy sk_buff To: Breno Leitao Cc: kuba@kernel.org, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260421073738.22110-1-zlatistiv@gmail.com> Content-Language: en-US From: "Nikola Z. Ivanov" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/21/26 11:19 AM, Breno Leitao wrote: > On Tue, Apr 21, 2026 at 10:37:38AM +0300, Nikola Z. Ivanov wrote: >> Syzbot reports a KMSAN uninit-value originating from >> nsim_dev_trap_skb_build, with the allocation also >> being performed in the same function. >> >> The cause of the KMSAN warning is a missing assignment of >> the tos and id fields of the ip header. >> >> Fix this by calling skb_put_zero instead of skb_put to >> guarantee null initialization. >> Additionally remove the now redundant zero assignments >> and reorder the remaining ones so that they more closely >> match the order of the fields as they appear in the ip header. >> >> Closes: https://syzkaller.appspot.com/bug?extid=23d7fcd204e3837866ff > How do you check in the report above that the missig un-initialized > fields are "tos" and "id"? > > Thanks for the fix, > --breno Hi Breno, I don't think it is visible here, my guess would be because the checksum calculator walks the header in small chunks instead of referencing its fields. The whole "KMSAN: uninit-value in irqentry_exit_to_kernel_mode_preempt" doesn't really sound quite right. Thank you!