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[2001:1ae9:2f0:fa00:5962:fdfb:2a9a:17bd]) by smtp.googlemail.com with ESMTPSA id j13-20020adff54d000000b0023655e51c33sm14610846wrp.4.2022.11.22.08.13.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Nov 2022 08:13:48 -0800 (PST) From: Petr Skocik To: "Eric W. Biederman" Cc: Oleg Nesterov , Kees Cook , Thomas Gleixner , Peter Zijlstra , Marco Elver , linux-kernel@vger.kernel.org, Petr Skocik Subject: [PATCH 0/1] *** Fix kill(-1,s) returning 0 on 0 kills *** Date: Tue, 22 Nov 2022 17:12:40 +0100 Message-Id: <20221122161240.137570-1-pskocik@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1750213704756704316?= X-GMAIL-MSGID: =?utf-8?q?1750213704756704316?= Hi. I've never sent a kernel patch before but this one seemed trivial, so I thought I'd give it a shot. My issue: kill(-1,s) on Linux doesn't return -ESCHR when it has nothing to kill. The code sample below demonstrates the problem, which gets fixed by the patch: #define _GNU_SOURCE #include #include #include #include #include #include #define VICTIM_UID 4200 //check these are safe to use on your system! #define UNUSED_UID 4300 int main(){ uid_t r,e,s; if(geteuid()) return 1; //requires root privileges //pipe to let the parent know when the child has changed ids int fds[2]; if(0>pipe(fds)) return 1; pid_t pid; if(0>(pid=fork())) return 1; else if(0==pid){ setreuid(VICTIM_UID,VICTIM_UID); getresuid(&r,&e,&s); printf("child: %u %u %u\n", r,e,s); close(fds[0]); close(fds[1]); //let the parent continue for(;;) pause(); } close(fds[1]); read(fds[0],&(char){0},1); //wait for uid change in the child #if 1 setreuid(VICTIM_UID,(uid_t)-1); seteuid(VICTIM_UID); #else setresuid(UNUSED_UID,VICTIM_UID,0); #endif getresuid(&r,&e,&s); printf("parent: %u %u %u\n", r,e,s); //4200 4200 0 int err = kill(-1,-111); (void)err; //test -EINVAL assert(err < 0 && errno == EINVAL); int rc = kill(-1,SIGTERM); //test 0 if(rc>=0) wait(0); int rc2 = kill(-1,SIGTERM); //test -ESCHR printf("1st kill ok==%d; 2nd kill ESRCH==%d\n", rc==0, rc2<0&& errno==ESRCH); } Thank you for considering the patch. Best regards, Petr S. Petr Skocik (1): Fix kill(-1,s) returning 0 on 0 kills kernel/signal.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)