Adhemerval Zanella fe05e1cb6d posix: Fix improper assert in Linux posix_spawn (BZ#22273) ... As noted by Florian Weimer, current Linux posix_spawn implementation can trigger an assert if the auxiliary process is terminated before actually setting the err member: 340 /* Child must set args.err to something non-negative - we rely on 341 the parent and child sharing VM. */ 342 args.err = -1; [...] 362 new_pid = CLONE (__spawni_child, STACK (stack, stack_size), stack_size, 363 CLONE_VM | CLONE_VFORK | SIGCHLD, &args); 364 365 if (new_pid > 0) 366 { 367 ec = args.err; 368 assert (ec >= 0); Another possible issue is killing the child between setting the err and actually calling execve. In this case the process will not ran, but posix_spawn also will not report any error: 269 270 args->err = 0; 271 args->exec (args->file, args->argv, args->envp); As suggested by Andreas Schwab, this patch removes the faulty assert and also handles any signal that happens before fork and execve as the spawn was successful (and thus relaying the handling to the caller to figure this out). Different than Florian, I can not see why using atomics to set err would help here, essentially the code runs sequentially (due CLONE_VFORK) and I think it would not be legal the compiler evaluate ec without checking for new_pid result (thus there is no need to compiler barrier). Summarizing the possible scenarios on posix_spawn execution, we have: 1. For default case with a success execution, args.err will be 0, pid will not be collected and it will be reported to caller. 2. For default failure case, args.err will be positive and the it will be collected by the waitpid. An error will be reported to the caller. 3. For the unlikely case where the process was terminated and not collected by a caller signal handler, it will be reported as succeful execution and not be collected by posix_spawn (since args.err will be 0). The caller will need to actually handle this case. 4. For the unlikely case where the process was terminated and collected by caller we have 3 other possible scenarios: 4.1. The auxiliary process was terminated with args.err equal to 0: it will handled as 1. (so it does not matter if we hit the pid reuse race since we won't possible collect an unexpected process). 4.2. The auxiliary process was terminated after execve (due a failure in calling it) and before setting args.err to -1: it will also be handle as 1. but with the issue of not be able to report the caller a possible execve failures. 4.3. The auxiliary process was terminated after args.err is set to -1: this is the case where it will be possible to hit the pid reuse case where we will need to collected the auxiliary pid but we can not be sure if it will be expected one. I think for this case we need to actually change waitpid to use WNOHANG to avoid hanging indefinitely on the call and report an error to caller since we can't differentiate between a default failure as 2. and a possible pid reuse race issue. Checked on x86_64-linux-gnu. * sysdeps/unix/sysv/linux/spawni.c (__spawnix): Handle the case where the auxiliary process is terminated by a signal before calling _exit or execve.		2017-10-20 16:25:59 -02:00
..
linux	posix: Fix improper assert in Linux posix_spawn (BZ#22273)	2017-10-20 16:25:59 -02:00