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Message-ID: <20230901080224.10889-1-ncopa@alpinelinux.org>
Date: Fri, 1 Sep 2023 10:02:00 +0200
From: Natanael Copa <ncopa@...inelinux.org>
To: musl@...ts.openwall.com
Cc: Natanael Copa <ncopa@...inelinux.org>
Subject: [PATCH] add close_range() syscall wrapper
close_range() is a syscall present in FreeBSD 8.0 and Linux 5.9. glibc
2.34 added a wrapper.
Expose it under _GNU_SOURCE similar to what GNU libc does. Also expose
it under _BSD_SOURCE since it is also a FreeBSD function.
---
This is a re-take of close_range() syscall wrapper. It was previously
discussed in mailing list: https://www.openwall.com/lists/musl/2022/08/18/5
Difference from previous submission:
- Use correct values for CLOSE_RANGE_UNSHARE and CLOSE_RANGE_CLOEXEC.
- Set errno on errors.
- Drop the (unsigned int) cast for flags, as it raised questions last
time.
I think it is a good idea to add this to musl because it is difficult to
the close before exec properly without it.
Most workaounrds currently out there are either parsing /proc or try to
close everything to maxfd reported by getrlimit(), sysconf() or
getdtablesize().
opendir("/proc/self/fd") is problematic becase 1) /proc may not be
mounted and 2) some versions of musl hangs on malloc between fork and
exec.
Trying to close everything between a maxfd is also problematic. On some
systems (under docker for example) the maxfd can be 1G, which
effectively results in a hang. (See https://github.com/k0sproject/k0s/pull/3436)
I think its better to encourage the use of close_range().
See also: https://github.com/OpenRC/openrc/pull/645
include/unistd.h | 3 +++
src/linux/close_range.c | 8 ++++++++
2 files changed, 11 insertions(+)
create mode 100644 src/linux/close_range.c
diff --git a/include/unistd.h b/include/unistd.h
index 5bc7f798..d89e3d4c 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -161,6 +161,9 @@ unsigned ualarm(unsigned, unsigned);
#define L_INCR 1
#define L_XTND 2
int brk(void *);
+#define CLOSE_RANGE_UNSHARE (1U << 1)
+#define CLOSE_RANGE_CLOEXEC (1U << 2)
+int close_range(unsigned int, unsigned int, int);
void *sbrk(intptr_t);
pid_t vfork(void);
int vhangup(void);
diff --git a/src/linux/close_range.c b/src/linux/close_range.c
new file mode 100644
index 00000000..258ba8bd
--- /dev/null
+++ b/src/linux/close_range.c
@@ -0,0 +1,8 @@
+#define _GNU_SOURCE
+#include <unistd.h>
+#include "syscall.h"
+
+int close_range(unsigned int first, unsigned int last, int flags)
+{
+ return __syscall_ret(syscall(SYS_close_range, first, last, flags));
+}
--
2.42.0
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