# git rev-parse -q --verify dbb5afad100a828c97e012c6106566d99f041db6^{commit}
dbb5afad100a828c97e012c6106566d99f041db6
already have revision, skipping fetch
# git checkout -q -f -B kisskb dbb5afad100a828c97e012c6106566d99f041db6
# git clean -qxdf
# < git log -1
# commit dbb5afad100a828c97e012c6106566d99f041db6
# Author: Oleg Nesterov <oleg@redhat.com>
# Date:   Wed May 12 15:33:08 2021 +0200
# 
#     ptrace: make ptrace() fail if the tracee changed its pid unexpectedly
#     
#     Suppose we have 2 threads, the group-leader L and a sub-theread T,
#     both parked in ptrace_stop(). Debugger tries to resume both threads
#     and does
#     
#             ptrace(PTRACE_CONT, T);
#             ptrace(PTRACE_CONT, L);
#     
#     If the sub-thread T execs in between, the 2nd PTRACE_CONT doesn not
#     resume the old leader L, it resumes the post-exec thread T which was
#     actually now stopped in PTHREAD_EVENT_EXEC. In this case the
#     PTHREAD_EVENT_EXEC event is lost, and the tracer can't know that the
#     tracee changed its pid.
#     
#     This patch makes ptrace() fail in this case until debugger does wait()
#     and consumes PTHREAD_EVENT_EXEC which reports old_pid. This affects all
#     ptrace requests except the "asynchronous" PTRACE_INTERRUPT/KILL.
#     
#     The patch doesn't add the new PTRACE_ option to not complicate the API,
#     and I _hope_ this won't cause any noticeable regression:
#     
#             - If debugger uses PTRACE_O_TRACEEXEC and the thread did an exec
#               and the tracer does a ptrace request without having consumed
#               the exec event, it's 100% sure that the thread the ptracer
#               thinks it is targeting does not exist anymore, or isn't the
#               same as the one it thinks it is targeting.
#     
#             - To some degree this patch adds nothing new. In the scenario
#               above ptrace(L) can fail with -ESRCH if it is called after the
#               execing sub-thread wakes the leader up and before it "steals"
#               the leader's pid.
#     
#     Test-case:
#     
#             #include <stdio.h>
#             #include <unistd.h>
#             #include <signal.h>
#             #include <sys/ptrace.h>
#             #include <sys/wait.h>
#             #include <errno.h>
#             #include <pthread.h>
#             #include <assert.h>
#     
#             void *tf(void *arg)
#             {
#                     execve("/usr/bin/true", NULL, NULL);
#                     assert(0);
#     
#                     return NULL;
#             }
#     
#             int main(void)
#             {
#                     int leader = fork();
#                     if (!leader) {
#                             kill(getpid(), SIGSTOP);
#     
#                             pthread_t th;
#                             pthread_create(&th, NULL, tf, NULL);
#                             for (;;)
#                                     pause();
#     
#                             return 0;
#                     }
#     
#                     waitpid(leader, NULL, WSTOPPED);
#     
#                     ptrace(PTRACE_SEIZE, leader, 0,
#                                     PTRACE_O_TRACECLONE | PTRACE_O_TRACEEXEC);
#                     waitpid(leader, NULL, 0);
#     
#                     ptrace(PTRACE_CONT, leader, 0,0);
#                     waitpid(leader, NULL, 0);
#     
#                     int status, thread = waitpid(-1, &status, 0);
#                     assert(thread > 0 && thread != leader);
#                     assert(status == 0x80137f);
#     
#                     ptrace(PTRACE_CONT, thread, 0,0);
#                     /*
#                      * waitid() because waitpid(leader, &status, WNOWAIT) does not
#                      * report status. Why ????
#                      *
#                      * Why WEXITED? because we have another kernel problem connected
#                      * to mt-exec.
#                      */
#                     siginfo_t info;
#                     assert(waitid(P_PID, leader, &info, WSTOPPED|WEXITED|WNOWAIT) == 0);
#                     assert(info.si_pid == leader && info.si_status == 0x0405);
#     
#                     /* OK, it sleeps in ptrace(PTRACE_EVENT_EXEC == 0x04) */
#                     assert(ptrace(PTRACE_CONT, leader, 0,0) == -1);
#                     assert(errno == ESRCH);
#     
#                     assert(leader == waitpid(leader, &status, WNOHANG));
#                     assert(status == 0x04057f);
#     
#                     assert(ptrace(PTRACE_CONT, leader, 0,0) == 0);
#     
#                     return 0;
#             }
#     
#     Signed-off-by: Oleg Nesterov <oleg@redhat.com>
#     Reported-by: Simon Marchi <simon.marchi@efficios.com>
#     Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
#     Acked-by: Pedro Alves <palves@redhat.com>
#     Acked-by: Simon Marchi <simon.marchi@efficios.com>
#     Acked-by: Jan Kratochvil <jan.kratochvil@redhat.com>
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-ld --version
# < git log --format=%s --max-count=1 dbb5afad100a828c97e012c6106566d99f041db6
# < make -s -j 48 ARCH=arm64 O=/kisskb/build/linus-rand_arm64-randconfig_arm64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-  randconfig
# Added to kconfig CONFIG_PREVENT_FIRMWARE_BUILD=y
# < make -s -j 48 ARCH=arm64 O=/kisskb/build/linus-rand_arm64-randconfig_arm64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-  help
# make -s -j 48 ARCH=arm64 O=/kisskb/build/linus-rand_arm64-randconfig_arm64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-  olddefconfig
.config:7191:warning: override: reassigning to symbol PREVENT_FIRMWARE_BUILD
# make -s -j 48 ARCH=arm64 O=/kisskb/build/linus-rand_arm64-randconfig_arm64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-  
Completed OK
# rm -rf /kisskb/build/linus-rand_arm64-randconfig_arm64-gcc8
# Build took: 0:07:54.778704