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([2804:1b3:a7c0:842a:1aa9:89f1:3b40:9ac]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-79f0af5e635sm6321269a12.22.2024.07.23.06.42.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Jul 2024 06:42:44 -0700 (PDT) From: Adhemerval Zanella To: libc-alpha@sourceware.org, Carlos O'Donell , Florian Weimer Subject: [PATCH v2 2/2] stdlib: Make abort/_Exit AS-safe (BZ 26275) Date: Tue, 23 Jul 2024 10:41:49 -0300 Message-ID: <20240723134235.1520483-3-adhemerval.zanella@linaro.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240723134235.1520483-1-adhemerval.zanella@linaro.org> References: <20240723134235.1520483-1-adhemerval.zanella@linaro.org> MIME-Version: 1.0 X-Spam-Status: No, score=-12.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces~patch=linaro.org@sourceware.org The recursive lock used on abort does not synchronize with new process creation (either by fork-like interfaces or posix_spawn ones), nor it is reinitialized after fork(). Also, the SIGABRT unblock before raise shows another race condition, where a fork or posix_spawn call by another thread just after the recursive lock release and before the SIGABRT raise might create programs with a non-expected signal mask. To fix the AS-safe, the raise issue without changing the process signal mask, and an AS-safe lock is used if a SIGABRT is installed or the process is blocked or ignored. The the signal mask change removal, there is no need to use a recursive lock. The lock is also on both _Fork and posix_spawn, to avoid the spawn process to see the abort handler as SIG_DFL. The posix_spawn possible issue is if the caller sets a SIG_IGN for SIGABRT, calls abort, and another thread issues posix_spawn just after the sigaction returns. With default options (not setting POSIX_SPAWN_SETSIGDEF), the process can still see SIG_DFL for SIGABRT, where it should be SIG_IGN. The fallback is also simplified, there is no need to use a loop of ABORT_INSTRUCTION after _exit (if the syscall does not terminate the process, the system is broken). Checked on x86_64-linux-gnu and aarch64-linux-gnu. --- include/bits/unistd_ext.h | 3 + include/stdlib.h | 6 + manual/startup.texi | 5 +- nptl/pthread_kill.c | 11 ++ posix/fork.c | 2 + signal/sigaction.c | 15 ++- stdlib/abort.c | 131 ++++++++------------- sysdeps/generic/internal-signals.h | 27 ++++- sysdeps/generic/internal-sigset.h | 26 ++++ sysdeps/htl/pthreadP.h | 2 + sysdeps/nptl/_Fork.c | 9 ++ sysdeps/nptl/pthreadP.h | 1 + sysdeps/unix/sysv/linux/internal-signals.h | 9 ++ sysdeps/unix/sysv/linux/internal-sigset.h | 2 +- sysdeps/unix/sysv/linux/spawni.c | 8 +- 15 files changed, 163 insertions(+), 94 deletions(-) create mode 100644 sysdeps/generic/internal-sigset.h diff --git a/include/bits/unistd_ext.h b/include/bits/unistd_ext.h index 277be05746..eeb07baf70 100644 --- a/include/bits/unistd_ext.h +++ b/include/bits/unistd_ext.h @@ -3,4 +3,7 @@ #ifndef _ISOMAC extern int __close_range (unsigned int lowfd, unsigned int highfd, int flags); libc_hidden_proto (__close_range); + +extern pid_t __gettid (void); +libc_hidden_proto (__gettid); #endif diff --git a/include/stdlib.h b/include/stdlib.h index 0cab3f5b56..07f074bcce 100644 --- a/include/stdlib.h +++ b/include/stdlib.h @@ -20,6 +20,7 @@ # include # include +# include extern __typeof (strtol_l) __strtol_l; extern __typeof (strtoul_l) __strtoul_l; @@ -77,6 +78,11 @@ libc_hidden_proto (__isoc23_strtoull_l) # define strtoull_l __isoc23_strtoull_l #endif +extern void __abort_fork_reset_child (void) attribute_hidden; +extern void __abort_lock_lock (internal_sigset_t *set) attribute_hidden; +extern void __abort_lock_unlock (const internal_sigset_t *set) + attribute_hidden; + libc_hidden_proto (exit) libc_hidden_proto (abort) libc_hidden_proto (getenv) diff --git a/manual/startup.texi b/manual/startup.texi index 747beed4d9..139e359258 100644 --- a/manual/startup.texi +++ b/manual/startup.texi @@ -1010,10 +1010,7 @@ for this function is in @file{stdlib.h}. @deftypefun void abort (void) @standards{ISO, stdlib.h} -@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@aculock{} @acucorrupt{}}} -@c The implementation takes a recursive lock and attempts to support -@c calls from signal handlers, but if we're in the middle of flushing or -@c using streams, we may encounter them in inconsistent states. +@safety{@prelim{}@mtsafe{}@asafe{}@acusafe{} The @code{abort} function causes abnormal program termination. This does not execute cleanup functions registered with @code{atexit} or @code{on_exit}. diff --git a/nptl/pthread_kill.c b/nptl/pthread_kill.c index 71e5a7bf5b..fa5121a583 100644 --- a/nptl/pthread_kill.c +++ b/nptl/pthread_kill.c @@ -69,6 +69,17 @@ __pthread_kill_implementation (pthread_t threadid, int signo, int no_tid) return ret; } +/* Send the signal SIGNO to the caller. Used by abort and called where the + signals are being already blocked and there is no need to synchronize with + exit_lock. */ +int +__pthread_raise_internal (int signo) +{ + /* Use the gettid syscall so it works after vfork. */ + int ret = INTERNAL_SYSCALL_CALL (tgkill, __getpid (), __gettid(), signo); + return INTERNAL_SYSCALL_ERROR_P (ret) ? INTERNAL_SYSCALL_ERRNO (ret) : 0; +} + int __pthread_kill_internal (pthread_t threadid, int signo) { diff --git a/posix/fork.c b/posix/fork.c index 298765a1ff..c2b476ff2d 100644 --- a/posix/fork.c +++ b/posix/fork.c @@ -84,6 +84,8 @@ __libc_fork (void) fork_system_setup_after_fork (); + call_function_static_weak (__abort_fork_reset_child); + /* Release malloc locks. */ call_function_static_weak (__malloc_fork_unlock_child); diff --git a/signal/sigaction.c b/signal/sigaction.c index 811062ae96..c2931b8b04 100644 --- a/signal/sigaction.c +++ b/signal/sigaction.c @@ -16,8 +16,9 @@ . */ #include -#include #include +#include +#include /* If ACT is not NULL, change the action for SIG to *ACT. If OACT is not NULL, put the old action for SIG in *OACT. */ @@ -30,7 +31,17 @@ __sigaction (int sig, const struct sigaction *act, struct sigaction *oact) return -1; } - return __libc_sigaction (sig, act, oact); + internal_sigset_t set; + + if (sig == SIGABRT) + __abort_lock_lock (&set); + + int r = __libc_sigaction (sig, act, oact); + + if (sig == SIGABRT) + __abort_lock_unlock (&set); + + return r; } libc_hidden_def (__sigaction) weak_alias (__sigaction, sigaction) diff --git a/stdlib/abort.c b/stdlib/abort.c index e2b84baac4..0ebebc55d1 100644 --- a/stdlib/abort.c +++ b/stdlib/abort.c @@ -15,13 +15,11 @@ License along with the GNU C Library; if not, see . */ -#include #include -#include -#include -#include -#include #include +#include +#include +#include /* Try to get a machine dependent instruction which will make the program crash. This is used in case everything else fails. */ @@ -35,89 +33,56 @@ struct abort_msg_s *__abort_msg; libc_hidden_def (__abort_msg) -/* We must avoid to run in circles. Therefore we remember how far we - already got. */ -static int stage; +/* The lock is used to prevent multiple thread to change the SIGABRT + to SIG_IGN while abort tries to change to SIG_DFL, and to avoid + a new process to see a wrong disposition if there is a SIGABRT + handler installed. */ +__libc_lock_define_initialized (static, lock); + +void +__abort_fork_reset_child (void) +{ + __libc_lock_init (lock); +} -/* We should be prepared for multiple threads trying to run abort. */ -__libc_lock_define_initialized_recursive (static, lock); +void +__abort_lock_lock (internal_sigset_t *set) +{ + internal_signal_block_all (set); + __libc_lock_lock (lock); +} +void +__abort_lock_unlock (const internal_sigset_t *set) +{ + __libc_lock_unlock (lock); + internal_signal_restore_set (set); +} /* Cause an abnormal program termination with core-dump. */ -void +_Noreturn void abort (void) { - struct sigaction act; - - /* First acquire the lock. */ - __libc_lock_lock_recursive (lock); - - /* Now it's for sure we are alone. But recursive calls are possible. */ - - /* Unblock SIGABRT. */ - if (stage == 0) - { - ++stage; - internal_sigset_t sigs; - internal_sigemptyset (&sigs); - internal_sigaddset (&sigs, SIGABRT); - internal_sigprocmask (SIG_UNBLOCK, &sigs, NULL); - } - - /* Send signal which possibly calls a user handler. */ - if (stage == 1) - { - /* This stage is special: we must allow repeated calls of - `abort' when a user defined handler for SIGABRT is installed. - This is risky since the `raise' implementation might also - fail but I don't see another possibility. */ - int save_stage = stage; - - stage = 0; - __libc_lock_unlock_recursive (lock); - - raise (SIGABRT); - - __libc_lock_lock_recursive (lock); - stage = save_stage + 1; - } - - /* There was a handler installed. Now remove it. */ - if (stage == 2) - { - ++stage; - memset (&act, '\0', sizeof (struct sigaction)); - act.sa_handler = SIG_DFL; - __sigfillset (&act.sa_mask); - act.sa_flags = 0; - __sigaction (SIGABRT, &act, NULL); - } - - /* Try again. */ - if (stage == 3) - { - ++stage; - raise (SIGABRT); - } - - /* Now try to abort using the system specific command. */ - if (stage == 4) - { - ++stage; - ABORT_INSTRUCTION; - } - - /* If we can't signal ourselves and the abort instruction failed, exit. */ - if (stage == 5) - { - ++stage; - _exit (127); - } - - /* If even this fails try to use the provided instruction to crash - or otherwise make sure we never return. */ - while (1) - /* Try for ever and ever. */ - ABORT_INSTRUCTION; + raise (SIGABRT); + + /* There is a SIGABRT handle installed and it returned, or SIGABRT was + blocked or ignored. In this case use a AS-safe lock to prevent sigaction + to change the signal dispositioni (it will block on __abort_lock), + reinstall the handle to abort the process, and re-raise the signal. + + The handle can not change again because sigaction blocks on the lock. */ + __abort_lock_lock (NULL); + + struct sigaction act = {.sa_handler = SIG_DFL, .sa_flags = 0 }; + __sigfillset (&act.sa_mask); + __libc_sigaction (SIGABRT, &act, NULL); + __pthread_raise_internal (SIGABRT); + internal_signal_unblock_signal (SIGABRT); + + /* This code should be unreachable, try the arch-specific code and the + syscall fallback. */ + ABORT_INSTRUCTION; + + _exit (127); } libc_hidden_def (abort) diff --git a/sysdeps/generic/internal-signals.h b/sysdeps/generic/internal-signals.h index 3db100be10..e031a96bac 100644 --- a/sysdeps/generic/internal-signals.h +++ b/sysdeps/generic/internal-signals.h @@ -20,6 +20,7 @@ # define __INTERNAL_SIGNALS_H #include +#include #include #include #include @@ -39,10 +40,32 @@ clear_internal_signals (sigset_t *set) { } -typedef sigset_t internal_sigset_t; - #define internal_sigemptyset(__s) __sigemptyset (__s) +#define internal_sigfillset(__s) __sigfillset (__s) #define internal_sigaddset(__s, __i) __sigaddset (__s, __i) #define internal_sigprocmask(__h, __s, __o) __sigprocmask (__h, __s, __o) +static inline void +internal_signal_block_all (internal_sigset_t *oset) +{ + internal_sigset_t set; + internal_sigfillset (&set); + internal_sigprocmask (SIG_BLOCK, &set, oset); +} + +static inline void +internal_signal_restore_set (const internal_sigset_t *set) +{ + internal_sigprocmask (SIG_SETMASK, set, NULL); +} + +static inline void +internal_signal_unblock_signal (int sig) +{ + internal_sigset_t set; + internal_sigemptyset (&set); + internal_sigaddset (&set, sig); + internal_sigprocmask (SIG_UNBLOCK, &set, NULL); +} + #endif /* __INTERNAL_SIGNALS_H */ diff --git a/sysdeps/generic/internal-sigset.h b/sysdeps/generic/internal-sigset.h new file mode 100644 index 0000000000..80279ffc47 --- /dev/null +++ b/sysdeps/generic/internal-sigset.h @@ -0,0 +1,26 @@ +/* Internal sigset_t definition. + Copyright (C) 2022-2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#ifndef _INTERNAL_SIGSET_H +#define _INTERNAL_SIGSET_H + +#include + +typedef sigset_t internal_sigset_t; + +#endif diff --git a/sysdeps/htl/pthreadP.h b/sysdeps/htl/pthreadP.h index cf8a2efe86..b0c9ceb23a 100644 --- a/sysdeps/htl/pthreadP.h +++ b/sysdeps/htl/pthreadP.h @@ -92,6 +92,8 @@ int __pthread_attr_setstack (pthread_attr_t *__attr, void *__stackaddr, int __pthread_attr_getstack (const pthread_attr_t *, void **, size_t *); void __pthread_testcancel (void); +#define __pthread_raise_internal(__sig) raise (__sig) + libc_hidden_proto (__pthread_self) #if IS_IN (libpthread) diff --git a/sysdeps/nptl/_Fork.c b/sysdeps/nptl/_Fork.c index ef199ddbc3..7d970e3978 100644 --- a/sysdeps/nptl/_Fork.c +++ b/sysdeps/nptl/_Fork.c @@ -17,11 +17,17 @@ . */ #include +#include #include pid_t _Fork (void) { + /* The lock acquisition needs to be AS-safe to avoid deadlock if _Fork is + called from the signal handler that has interrupted fork itself. */ + internal_sigset_t set; + __abort_lock_lock (&set); + pid_t pid = arch_fork (&THREAD_SELF->tid); if (pid == 0) { @@ -44,6 +50,9 @@ _Fork (void) INTERNAL_SYSCALL_CALL (set_robust_list, &self->robust_head, sizeof (struct robust_list_head)); } + + __abort_lock_unlock (&set); + return pid; } libc_hidden_def (_Fork) diff --git a/sysdeps/nptl/pthreadP.h b/sysdeps/nptl/pthreadP.h index 30e8a2d177..b8ed954e5a 100644 --- a/sysdeps/nptl/pthreadP.h +++ b/sysdeps/nptl/pthreadP.h @@ -508,6 +508,7 @@ libc_hidden_proto (__pthread_kill) extern int __pthread_cancel (pthread_t th); extern int __pthread_kill_internal (pthread_t threadid, int signo) attribute_hidden; +extern int __pthread_raise_internal (int signo) attribute_hidden; extern void __pthread_exit (void *value) __attribute__ ((__noreturn__)); libc_hidden_proto (__pthread_exit) extern int __pthread_join (pthread_t threadid, void **thread_return); diff --git a/sysdeps/unix/sysv/linux/internal-signals.h b/sysdeps/unix/sysv/linux/internal-signals.h index a6fae59aaa..6e3a3d7692 100644 --- a/sysdeps/unix/sysv/linux/internal-signals.h +++ b/sysdeps/unix/sysv/linux/internal-signals.h @@ -90,6 +90,15 @@ internal_signal_restore_set (const internal_sigset_t *set) __NSIG_BYTES); } +static inline void +internal_signal_unblock_signal (int sig) +{ + internal_sigset_t set; + internal_sigemptyset (&set); + internal_sigaddset (&set, sig); + INTERNAL_SYSCALL_CALL (rt_sigprocmask, SIG_UNBLOCK, &set, NULL, + __NSIG_BYTES); +} /* It is used on timer_create code directly on sigwaitinfo call, so it can not use the internal_sigset_t definitions. */ diff --git a/sysdeps/unix/sysv/linux/internal-sigset.h b/sysdeps/unix/sysv/linux/internal-sigset.h index 5d7020b42d..4b19affd75 100644 --- a/sysdeps/unix/sysv/linux/internal-sigset.h +++ b/sysdeps/unix/sysv/linux/internal-sigset.h @@ -21,7 +21,7 @@ #include -typedef struct +typedef struct _internal_sigset_t { unsigned long int __val[__NSIG_WORDS]; } internal_sigset_t; diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c index f57e92815e..be72fa716f 100644 --- a/sysdeps/unix/sysv/linux/spawni.c +++ b/sysdeps/unix/sysv/linux/spawni.c @@ -383,7 +383,11 @@ __spawnix (int *pid, const char *file, args.pidfd = 0; args.xflags = xflags; - internal_signal_block_all (&args.oldmask); + /* Avoid the potential issues is if caller sets a SIG_IGN for SIGABRT, calls + abort, and another thread issues posix_spawn just after the sigaction + returns. With default options (not setting POSIX_SPAWN_SETSIGDEF), the + process can still see SIG_DFL for SIGABRT, where it should be SIG_IGN. */ + __abort_lock_lock (&args.oldmask); /* The clone flags used will create a new child that will run in the same memory space (CLONE_VM) and the execution of calling thread will be @@ -474,7 +478,7 @@ __spawnix (int *pid, const char *file, if ((ec == 0) && (pid != NULL)) *pid = use_pidfd ? args.pidfd : new_pid; - internal_signal_restore_set (&args.oldmask); + __abort_lock_unlock (&args.oldmask); __pthread_setcancelstate (state, NULL);