Commit 6580807da14c423f0d0a708108e6df6ebc8bc83d
Committed by
Linus Torvalds
1 parent
c6a47cc2cc
Exists in
master
and in
4 other branches
ptrace: copy_process() should disable stepping
If the tracee calls fork() after PTRACE_SINGLESTEP, the forked child starts with TIF_SINGLESTEP/X86_EFLAGS_TF bits copied from ptraced parent. This is not right, especially when the new child is not auto-attaced: in this case it is killed by SIGTRAP. Change copy_process() to call user_disable_single_step(). Tested on x86. Test-case: #include <stdio.h> #include <unistd.h> #include <signal.h> #include <sys/ptrace.h> #include <sys/wait.h> #include <assert.h> int main(void) { int pid, status; if (!(pid = fork())) { assert(ptrace(PTRACE_TRACEME) == 0); kill(getpid(), SIGSTOP); if (!fork()) { /* kernel bug: this child will be killed by SIGTRAP */ printf("Hello world\n"); return 43; } wait(&status); return WEXITSTATUS(status); } for (;;) { assert(pid == wait(&status)); if (WIFEXITED(status)) break; assert(ptrace(PTRACE_SINGLESTEP, pid, 0,0) == 0); } assert(WEXITSTATUS(status) == 43); return 0; } Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Showing 1 changed file with 3 additions and 2 deletions Side-by-side Diff
kernel/fork.c
... | ... | @@ -1210,9 +1210,10 @@ |
1210 | 1210 | p->sas_ss_sp = p->sas_ss_size = 0; |
1211 | 1211 | |
1212 | 1212 | /* |
1213 | - * Syscall tracing should be turned off in the child regardless | |
1214 | - * of CLONE_PTRACE. | |
1213 | + * Syscall tracing and stepping should be turned off in the | |
1214 | + * child regardless of CLONE_PTRACE. | |
1215 | 1215 | */ |
1216 | + user_disable_single_step(p); | |
1216 | 1217 | clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE); |
1217 | 1218 | #ifdef TIF_SYSCALL_EMU |
1218 | 1219 | clear_tsk_thread_flag(p, TIF_SYSCALL_EMU); |