From faf904b9f9789d6e921ab0bf0fb788594f97ef3b Mon Sep 17 00:00:00 2001 From: Narayan Kamath Date: Mon, 7 Nov 2016 16:22:48 +0000 Subject: Zygote : Block SIGCHLD during fork. We close the android logging related sockets prior as late as possible before every fork to avoid having to whitelist them. If one of the zygote's children dies after this point (but prior to the fork), we can end up reopening the logging sockets from the SIGCHLD signal handler. To prevent this from happening, block SIGCHLD during this critical section. Bug: 32693692 Test: Manual (cherry picked from commit e9a525829a354c92983a35455ccab16d1b0d3892) Zygote: Unblock SIGCHLD in the parent after fork. Follow up to change e9a525829a354c92983a. Allows the zygote to receive SIGCHLD again and prevents the zygote from getting into a zombie state if it's killed. Contributed-By: rhed_jao Bug: 32693692 Test: manual (cherry picked from commit c7161f756e86b98f2244a04d9207b47149965fd7) Change-Id: If89903a29c84dfc9b056f9e19618046874bba689 (cherry picked from commit dfcc79ee8ecd4166cba19be7493c6175cb0c65a9) --- core/jni/com_android_internal_os_Zygote.cpp | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/core/jni/com_android_internal_os_Zygote.cpp b/core/jni/com_android_internal_os_Zygote.cpp index d1fe07bcc779..f94c86150dc6 100644 --- a/core/jni/com_android_internal_os_Zygote.cpp +++ b/core/jni/com_android_internal_os_Zygote.cpp @@ -454,6 +454,20 @@ static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArra SetForkLoad(true); #endif + sigset_t sigchld; + sigemptyset(&sigchld); + sigaddset(&sigchld, SIGCHLD); + + // Temporarily block SIGCHLD during forks. The SIGCHLD handler might + // log, which would result in the logging FDs we close being reopened. + // This would cause failures because the FDs are not whitelisted. + // + // Note that the zygote process is single threaded at this point. + if (sigprocmask(SIG_BLOCK, &sigchld, nullptr) == -1) { + ALOGE("sigprocmask(SIG_SETMASK, { SIGCHLD }) failed: %s", strerror(errno)); + RuntimeAbort(env, __LINE__, "Call to sigprocmask(SIG_BLOCK, { SIGCHLD }) failed."); + } + // Close any logging related FDs before we start evaluating the list of // file descriptors. __android_log_close(); @@ -485,6 +499,11 @@ static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArra RuntimeAbort(env, __LINE__, "Unable to reopen whitelisted descriptors."); } + if (sigprocmask(SIG_UNBLOCK, &sigchld, nullptr) == -1) { + ALOGE("sigprocmask(SIG_SETMASK, { SIGCHLD }) failed: %s", strerror(errno)); + RuntimeAbort(env, __LINE__, "Call to sigprocmask(SIG_UNBLOCK, { SIGCHLD }) failed."); + } + // Keep capabilities across UID change, unless we're staying root. if (uid != 0) { EnableKeepCapabilities(env); @@ -618,6 +637,11 @@ static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArra SetForkLoad(false); #endif + // We blocked SIGCHLD prior to a fork, we unblock it here. + if (sigprocmask(SIG_UNBLOCK, &sigchld, nullptr) == -1) { + ALOGE("sigprocmask(SIG_SETMASK, { SIGCHLD }) failed: %s", strerror(errno)); + RuntimeAbort(env, __LINE__, "Call to sigprocmask(SIG_UNBLOCK, { SIGCHLD }) failed."); + } } return pid; } -- cgit v1.2.3