From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 12 Feb 2024 10:23:54 +0000 (+0100)
Subject: missing: change our close_range() syscall wrapper to map glibc's
X-Git-Tag: v256-rc1~897
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=39d69836ad47788b7a4ec13f8a4145d5118a50a5;p=thirdparty%2Fsystemd.git

missing: change our close_range() syscall wrapper to map glibc's

So glibc exposes a close_range() syscall wrapper now, but they decided
to use "unsigned" as type for the fds. Which is a bit weird, because fds
are universally understood to be "int". The kernel internally uses
"unsigned", both for close() and for close_range(), but weirdly,
userspace didn't fix that for close_range() unlike what they did for
close()... Weird.

But anyway, let's follow suit, and make our wrapper match glibc's.

Fixes #31270
---

diff --git a/src/basic/fd-util.c b/src/basic/fd-util.c
index 38866ebb782..d2ff456cc7b 100644
--- a/src/basic/fd-util.c
+++ b/src/basic/fd-util.c
@@ -308,7 +308,7 @@ static int close_all_fds_special_case(const int except[], size_t n_except) {
         case 0:
                 /* Close everything. Yay! */
 
-                if (close_range(3, -1, 0) >= 0)
+                if (close_range(3, INT_MAX, 0) >= 0)
                         return 1;
 
                 if (ERRNO_IS_NOT_SUPPORTED(errno) || ERRNO_IS_PRIVILEGE(errno)) {
@@ -419,7 +419,7 @@ int close_all_fds(const int except[], size_t n_except) {
                                 if (sorted[n_sorted-1] >= INT_MAX) /* Dont let the addition below overflow */
                                         return 0;
 
-                                if (close_range(sorted[n_sorted-1] + 1, -1, 0) >= 0)
+                                if (close_range(sorted[n_sorted-1] + 1, INT_MAX, 0) >= 0)
                                         return 0;
 
                                 if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
diff --git a/src/basic/missing_syscall.h b/src/basic/missing_syscall.h
index d795efd8f28..86280771c49 100644
--- a/src/basic/missing_syscall.h
+++ b/src/basic/missing_syscall.h
@@ -412,23 +412,14 @@ static inline int missing_execveat(int dirfd, const char *pathname,
 /* ======================================================================= */
 
 #if !HAVE_CLOSE_RANGE
-static inline int missing_close_range(int first_fd, int end_fd, unsigned flags) {
+static inline int missing_close_range(unsigned first_fd, unsigned end_fd, unsigned flags) {
 #  ifdef __NR_close_range
         /* Kernel-side the syscall expects fds as unsigned integers (just like close() actually), while
-         * userspace exclusively uses signed integers for fds. We don't know just yet how glibc is going to
-         * wrap this syscall, but let's assume it's going to be similar to what they do for close(),
-         * i.e. make the same unsigned → signed type change from the raw kernel syscall compared to the
-         * userspace wrapper. There's only one caveat for this: unlike for close() there's the special
-         * UINT_MAX fd value for the 'end_fd' argument. Let's safely map that to -1 here. And let's refuse
-         * any other negative values. */
-        if ((first_fd < 0) || (end_fd < 0 && end_fd != -1)) {
-                errno = -EBADF;
-                return -1;
-        }
-
+         * userspace exclusively uses signed integers for fds. glibc chose to expose it 1:1 however, hence we
+         * do so here too, even if we end up passing signed fds to it most of the time. */
         return syscall(__NR_close_range,
-                       (unsigned) first_fd,
-                       end_fd == -1 ? UINT_MAX : (unsigned) end_fd, /* Of course, the compiler should figure out that this is the identity mapping IRL */
+                       first_fd,
+                       end_fd,
                        flags);
 #  else
         errno = ENOSYS;