Linux gained new close_range() syscall (in v5.9) that allows closing a range of FDs in a single syscall. Ideally, we would use it to close FDs when spawning a process (e.g. via virCommand module). Glibc has close_range() wrapper over the syscall, which falls back to iterative closing of all FDs inside the range if running under older kernel. We don't wan that as in that case we might just close opened FDs (see Linux version of virCommandMassClose()). And musl doesn't have close_range() at all. Therefore, call syscall directly. Now, mass close of FDs happen in a fork()-ed off child. While it could detect whether the kernel does support close_range(), it has no way of passing this info back to the parent and thus each child would need to query it again and again. Since this can't change while we are running we can cache the information - hence virCloseRangeInit(). Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- src/libvirt_private.syms | 3 ++ src/util/virfile.c | 89 ++++++++++++++++++++++++++++++++++++++++ src/util/virfile.h | 4 ++ 3 files changed, 96 insertions(+) diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms index da60c965dd..3782f7f3c7 100644 --- a/src/libvirt_private.syms +++ b/src/libvirt_private.syms @@ -2269,6 +2269,9 @@ saferead; safewrite; safezero; virBuildPathInternal; +virCloseRange; +virCloseRangeInit; +virCloseRangeIsSupported; virDirClose; virDirCreate; virDirIsEmpty; diff --git a/src/util/virfile.c b/src/util/virfile.c index fe456596ae..7696910e00 100644 --- a/src/util/virfile.c +++ b/src/util/virfile.c @@ -87,6 +87,7 @@ #include "virlog.h" #include "virprocess.h" #include "virstring.h" +#include "virthread.h" #include "virutil.h" #include "virsocket.h" @@ -109,6 +110,9 @@ VIR_LOG_INIT("util.file"); # define O_DIRECT 0 #endif +static virOnceControl virCloseRangeOnce = VIR_ONCE_CONTROL_INITIALIZER; +static bool virCloseRangeSupported; + int virFileClose(int *fdptr, virFileCloseFlags flags) { int saved_errno = 0; @@ -176,6 +180,91 @@ FILE *virFileFdopen(int *fdptr, const char *mode) } +static int +virCloseRangeImpl(unsigned int first G_GNUC_UNUSED, + unsigned int last G_GNUC_UNUSED) +{ +#if defined(WITH_SYS_SYSCALL_H) && defined(__NR_close_range) + return syscall(__NR_close_range, first, last, 0); +#endif + + errno = ENOSYS; + return -1; +} + + +static void +virCloseRangeOnceInit(void) +{ + int fd[2] = { -1, -1}; + + if (virPipeQuiet(fd) < 0) + return; + + VIR_FORCE_CLOSE(fd[1]); + if (virCloseRangeImpl(fd[0], fd[0]) < 0) { + VIR_FORCE_CLOSE(fd[0]); + return; + } + + virCloseRangeSupported = true; +} + + +/** + * virCloseRange: + * + * Closes all open file descriptors from @first to @last (included). + * + * Returns: 0 on success, + * -1 on failure (with errno set). + */ +int +virCloseRange(unsigned int first, + unsigned int last) +{ + if (virCloseRangeInit() < 0) + return -1; + + if (!virCloseRangeSupported) { + errno = ENOSYS; + return -1; + } + + return virCloseRangeImpl(first, last); +} + + +/** + * virCloseRangeInit: + * + * Detects whether close_range() is available and cache the result. + */ +int +virCloseRangeInit(void) +{ + if (virOnce(&virCloseRangeOnce, virCloseRangeOnceInit) < 0) + return -1; + + return 0; +} + + +/** + * virCloseRangeIsSupported: + * + * Returns whether close_range() is supported or not. + */ +bool +virCloseRangeIsSupported(void) +{ + if (virCloseRangeInit() < 0) + return false; + + return virCloseRangeSupported; +} + + /** * virFileDirectFdFlag: * diff --git a/src/util/virfile.h b/src/util/virfile.h index 60bb1d64e7..be0b02fdf0 100644 --- a/src/util/virfile.h +++ b/src/util/virfile.h @@ -61,6 +61,10 @@ static inline void virForceCloseHelper(int *fd) ignore_value(virFileClose(fd, VIR_FILE_CLOSE_PRESERVE_ERRNO)); } +int virCloseRange(unsigned int from, unsigned int to); +int virCloseRangeInit(void); +bool virCloseRangeIsSupported(void); + /* For use on normal paths; caller must check return value, and failure sets errno per close. */ #define VIR_CLOSE(FD) virFileClose(&(FD), 0) -- 2.41.0

It is handy to close all FDs from given FD to infinity. On FreeBSD the libc even has a function for that: closefrom(). It was ported to glibc too, but not musl. At least glibc implementation falls back to calling: close_range(from, ~0U, 0); Now that we have a wrapper for close_range() we implement closefrom() trivially. Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- src/libvirt_private.syms | 1 + src/util/virfile.c | 21 +++++++++++++++++++++ src/util/virfile.h | 1 + 3 files changed, 23 insertions(+) diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms index 3782f7f3c7..9477a07834 100644 --- a/src/libvirt_private.syms +++ b/src/libvirt_private.syms @@ -2269,6 +2269,7 @@ saferead; safewrite; safezero; virBuildPathInternal; +virCloseFrom; virCloseRange; virCloseRangeInit; virCloseRangeIsSupported; diff --git a/src/util/virfile.c b/src/util/virfile.c index 7696910e00..c74bdd1264 100644 --- a/src/util/virfile.c +++ b/src/util/virfile.c @@ -265,6 +265,27 @@ virCloseRangeIsSupported(void) } +/** + * virCloseFrom: + * + * Closes all open file descriptors greater than or equal to @fromfd. + * + * Returns: 0 on success, + * -1 on error (with errno set). + */ +int +virCloseFrom(int fromfd) +{ +#ifdef __FreeBSD__ + /* FreeBSD has closefrom() since FreeBSD-8.0, i.e. since 2009. */ + closefrom(fromfd); + return 0; +#else /* !__FreeBSD__ */ + return virCloseRange(fromfd, ~0U); +#endif /* !__FreeBSD__ */ +} + + /** * virFileDirectFdFlag: * diff --git a/src/util/virfile.h b/src/util/virfile.h index be0b02fdf0..adc032ba33 100644 --- a/src/util/virfile.h +++ b/src/util/virfile.h @@ -64,6 +64,7 @@ static inline void virForceCloseHelper(int *fd) int virCloseRange(unsigned int from, unsigned int to); int virCloseRangeInit(void); bool virCloseRangeIsSupported(void); +int virCloseFrom(int fromfd); /* For use on normal paths; caller must check return value, and failure sets errno per close. */ -- 2.41.0

This is brand new way of closing FDs before exec(). We need to close all FDs except those we want to explicitly pass to avoid leaking FDs into the child. Historically, we've done this by either iterating over all opened FDs and closing them one by one (or preserving them), or by iterating over an FD interval [2 ... N] and closing them one by one followed by calling closefrom(N + 1). This is a lot of syscalls. That's why Linux kernel developers introduced new close_from syscall. It closes all FDs within given range, in a single syscall. Since we keep list of FDs we want to preserve and pass to the child process, we can use this syscall to close all FDs in between. We don't even need to care about opened FDs. Of course, we have to check whether the syscall is available and fall back to the old implementation if it isn't. Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- src/util/vircommand.c | 77 ++++++++++++++++++++++++++++++++++++++++--- tests/commandtest.c | 2 ++ 2 files changed, 75 insertions(+), 4 deletions(-) diff --git a/src/util/vircommand.c b/src/util/vircommand.c index 867f45b57b..5f094c625a 100644 --- a/src/util/vircommand.c +++ b/src/util/vircommand.c @@ -527,10 +527,10 @@ virCommandMassCloseGetFDsGeneric(virCommand *cmd G_GNUC_UNUSED, # endif /* !__linux__ */ static int -virCommandMassClose(virCommand *cmd, - int childin, - int childout, - int childerr) +virCommandMassCloseFrom(virCommand *cmd, + int childin, + int childout, + int childerr) { g_autoptr(virBitmap) fds = NULL; int openmax = sysconf(_SC_OPEN_MAX); @@ -597,6 +597,75 @@ virCommandMassClose(virCommand *cmd, } +static int +virCommandMassCloseRange(virCommand *cmd, + int childin, + int childout, + int childerr) +{ + g_autoptr(virBitmap) fds = virBitmapNew(0); + ssize_t first; + ssize_t last; + size_t i; + + virBitmapSetBitExpand(fds, childin); + virBitmapSetBitExpand(fds, childout); + virBitmapSetBitExpand(fds, childerr); + + for (i = 0; i < cmd->npassfd; i++) { + int fd = cmd->passfd[i].fd; + + virBitmapSetBitExpand(fds, fd); + + if (virSetInherit(fd, true) < 0) { + virReportSystemError(errno, _("failed to preserve fd %1$d"), fd); + return -1; + } + } + + first = 2; + while ((last = virBitmapNextSetBit(fds, first)) >= 0) { + if (first + 1 == last) { + first = last; + continue; + } + + /* Preserve @first and @last and close everything in between. */ + if (virCloseRange(first + 1, last - 1) < 0) { + virReportSystemError(errno, + _("Unable to mass close FDs (first=%1$zd, last=%2$zd)"), + first + 1, last - 1); + return -1; + } + + first = last; + } + + if (virCloseRange(first + 1, ~0U) < 0) { + virReportSystemError(errno, + _("Unable to mass close FDs (first=%1$zd, last=%2$d"), + first + 1, ~0U); + return -1; + } + + return 0; +} + + + +static int +virCommandMassClose(virCommand *cmd, + int childin, + int childout, + int childerr) +{ + if (virCloseRangeIsSupported()) + return virCommandMassCloseRange(cmd, childin, childout, childerr); + + return virCommandMassCloseFrom(cmd, childin, childout, childerr); +} + + /* * virExec: * @cmd virCommand * containing all information about the program to diff --git a/tests/commandtest.c b/tests/commandtest.c index 688cf59160..aa108ce583 100644 --- a/tests/commandtest.c +++ b/tests/commandtest.c @@ -1247,6 +1247,8 @@ mymain(void) setpgid(0, 0); ignore_value(setsid()); + virCloseRangeInit(); + /* Our test expects particular fd values; to get that, we must not * leak fds that we inherited from a lazy parent. At the same * time, virInitialize may open some fds (perhaps via third-party -- 2.41.0