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-rw-r--r--src/basic/tmpfile-util.c70
-rw-r--r--src/basic/tmpfile-util.h4
-rw-r--r--src/boot/bootctl-install.c10
-rw-r--r--src/coredump/coredump.c2
-rw-r--r--src/portable/portable.c2
-rw-r--r--src/shared/copy.c52
-rw-r--r--src/test/test-tmpfiles.c20
7 files changed, 97 insertions, 63 deletions
diff --git a/src/basic/tmpfile-util.c b/src/basic/tmpfile-util.c
index 95adf9d374..379d81d5c8 100644
--- a/src/basic/tmpfile-util.c
+++ b/src/basic/tmpfile-util.c
@@ -14,6 +14,7 @@
#include "path-util.h"
#include "process-util.h"
#include "random-util.h"
+#include "stat-util.h"
#include "stdio-util.h"
#include "string-util.h"
#include "tmpfile-util.h"
@@ -328,24 +329,71 @@ int fopen_tmpfile_linkable(const char *target, int flags, char **ret_path, FILE
return 0;
}
-int link_tmpfile(int fd, const char *path, const char *target) {
+static int link_fd(int fd, int newdirfd, const char *newpath) {
+ int r;
+
+ assert(fd >= 0);
+ assert(newdirfd >= 0 || newdirfd == AT_FDCWD);
+ assert(newpath);
+
+ /* Try symlinking via /proc/fd/ first. */
+ r = RET_NERRNO(linkat(AT_FDCWD, FORMAT_PROC_FD_PATH(fd), newdirfd, newpath, AT_SYMLINK_FOLLOW));
+ if (r != -ENOENT)
+ return r;
+
+ /* Fall back to symlinking via AT_EMPTY_PATH as fallback (this requires CAP_DAC_READ_SEARCH and a
+ * more recent kernel, but does not require /proc/ mounted) */
+ if (proc_mounted() != 0)
+ return r;
+
+ return RET_NERRNO(linkat(fd, "", newdirfd, newpath, AT_EMPTY_PATH));
+}
+
+int link_tmpfile(int fd, const char *path, const char *target, bool replace) {
+ _cleanup_free_ char *tmp = NULL;
+ int r;
+
assert(fd >= 0);
assert(target);
- /* Moves a temporary file created with open_tmpfile() above into its final place. if "path" is NULL an fd
- * created with O_TMPFILE is assumed, and linkat() is used. Otherwise it is assumed O_TMPFILE is not supported
- * on the directory, and renameat2() is used instead.
- *
- * Note that in both cases we will not replace existing files. This is because linkat() does not support this
- * operation currently (renameat2() does), and there is no nice way to emulate this. */
+ /* Moves a temporary file created with open_tmpfile() above into its final place. If "path" is NULL
+ * an fd created with O_TMPFILE is assumed, and linkat() is used. Otherwise it is assumed O_TMPFILE
+ * is not supported on the directory, and renameat2() is used instead. */
+
+ if (path) {
+ if (replace)
+ return RET_NERRNO(rename(path, target));
- if (path)
return rename_noreplace(AT_FDCWD, path, AT_FDCWD, target);
+ }
+
+ r = link_fd(fd, AT_FDCWD, target);
+ if (r != -EEXIST || !replace)
+ return r;
+
+ /* So the target already exists and we were asked to replace it. That sucks a bit, since the kernel's
+ * linkat() logic does not allow that. We work-around this by linking the file to a random name
+ * first, and then renaming that to the final name. This reintroduces the race O_TMPFILE kinda is
+ * trying to fix, but at least the vulnerability window (i.e. where the file is linked into the file
+ * system under a temporary name) is very short. */
+
+ r = tempfn_random(target, NULL, &tmp);
+ if (r < 0)
+ return r;
+
+ if (link_fd(fd, AT_FDCWD, tmp) < 0)
+ return -EEXIST; /* propagate original error */
- return RET_NERRNO(linkat(AT_FDCWD, FORMAT_PROC_FD_PATH(fd), AT_FDCWD, target, AT_SYMLINK_FOLLOW));
+ r = RET_NERRNO(rename(tmp, target));
+ if (r < 0) {
+ (void) unlink(tmp);
+ return r;
+ }
+
+ return 0;
}
-int flink_tmpfile(FILE *f, const char *path, const char *target) {
+int flink_tmpfile(FILE *f, const char *path, const char *target, bool replace) {
int fd, r;
assert(f);
@@ -359,7 +407,7 @@ int flink_tmpfile(FILE *f, const char *path, const char *target) {
if (r < 0)
return r;
- return link_tmpfile(fd, path, target);
+ return link_tmpfile(fd, path, target, replace);
}
int mkdtemp_malloc(const char *template, char **ret) {
diff --git a/src/basic/tmpfile-util.h b/src/basic/tmpfile-util.h
index e5b7709e3f..4665dafb24 100644
--- a/src/basic/tmpfile-util.h
+++ b/src/basic/tmpfile-util.h
@@ -25,8 +25,8 @@ int open_tmpfile_unlinkable(const char *directory, int flags);
int open_tmpfile_linkable(const char *target, int flags, char **ret_path);
int fopen_tmpfile_linkable(const char *target, int flags, char **ret_path, FILE **ret_file);
-int link_tmpfile(int fd, const char *path, const char *target);
-int flink_tmpfile(FILE *f, const char *path, const char *target);
+int link_tmpfile(int fd, const char *path, const char *target, bool replace);
+int flink_tmpfile(FILE *f, const char *path, const char *target, bool replace);
int mkdtemp_malloc(const char *template, char **ret);
int mkdtemp_open(const char *template, int flags, char **ret);
diff --git a/src/boot/bootctl-install.c b/src/boot/bootctl-install.c
index ebb0d486c9..624b88abe3 100644
--- a/src/boot/bootctl-install.c
+++ b/src/boot/bootctl-install.c
@@ -426,12 +426,14 @@ static int install_binaries(const char *esp_path, const char *arch, bool force)
static int install_loader_config(const char *esp_path) {
_cleanup_(unlink_and_freep) char *t = NULL;
_cleanup_fclose_ FILE *f = NULL;
- const char *p;
+ _cleanup_free_ char *p = NULL;
int r;
assert(arg_make_entry_directory >= 0);
- p = prefix_roota(esp_path, "/loader/loader.conf");
+ p = path_join(esp_path, "/loader/loader.conf");
+ if (!p)
+ return log_oom();
if (access(p, F_OK) >= 0) /* Silently skip creation if the file already exists (early check) */
return 0;
@@ -447,7 +449,7 @@ static int install_loader_config(const char *esp_path) {
fprintf(f, "default %s-*\n", arg_entry_token);
}
- r = flink_tmpfile(f, t, p);
+ r = flink_tmpfile(f, t, p, /* replace= */ false);
if (r == -EEXIST)
return 0; /* Silently skip creation if the file exists now (recheck) */
if (r < 0)
@@ -476,7 +478,7 @@ static int install_loader_specification(const char *root) {
fprintf(f, "type1\n");
- r = flink_tmpfile(f, t, p);
+ r = flink_tmpfile(f, t, p, /* replace= */ false);
if (r == -EEXIST)
return 0; /* Silently skip creation if the file exists now (recheck) */
if (r < 0)
diff --git a/src/coredump/coredump.c b/src/coredump/coredump.c
index d9db98bf32..d5d1f49d08 100644
--- a/src/coredump/coredump.c
+++ b/src/coredump/coredump.c
@@ -277,7 +277,7 @@ static int fix_permissions(
if (r < 0)
return log_error_errno(r, "Failed to sync coredump %s: %m", coredump_tmpfile_name(filename));
- r = link_tmpfile(fd, filename, target);
+ r = link_tmpfile(fd, filename, target, /* replace= */ false);
if (r < 0)
return log_error_errno(r, "Failed to move coredump %s into place: %m", target);
diff --git a/src/portable/portable.c b/src/portable/portable.c
index 7811833fac..377e1a9937 100644
--- a/src/portable/portable.c
+++ b/src/portable/portable.c
@@ -1188,7 +1188,7 @@ static int attach_unit_file(
if (fchmod(fd, 0644) < 0)
return log_debug_errno(errno, "Failed to change unit file access mode for '%s': %m", path);
- r = link_tmpfile(fd, tmp, path);
+ r = link_tmpfile(fd, tmp, path, /* replace= */ false);
if (r < 0)
return log_debug_errno(r, "Failed to install unit file '%s': %m", path);
diff --git a/src/shared/copy.c b/src/shared/copy.c
index 9963e10f4d..146293acdf 100644
--- a/src/shared/copy.c
+++ b/src/shared/copy.c
@@ -1452,43 +1452,16 @@ int copy_file_atomic_full(
assert(from);
assert(to);
- /* We try to use O_TMPFILE here to create the file if we can. Note that this only works if COPY_REPLACE is not
- * set though as we need to use linkat() for linking the O_TMPFILE file into the file system but that system
- * call can't replace existing files. Hence, if COPY_REPLACE is set we create a temporary name in the file
- * system right-away and unconditionally which we then can renameat() to the right name after we completed
- * writing it. */
-
- if (copy_flags & COPY_REPLACE) {
- _cleanup_free_ char *f = NULL;
-
- r = tempfn_random(to, NULL, &f);
+ if (copy_flags & COPY_MAC_CREATE) {
+ r = mac_selinux_create_file_prepare(to, S_IFREG);
if (r < 0)
return r;
-
- if (copy_flags & COPY_MAC_CREATE) {
- r = mac_selinux_create_file_prepare(to, S_IFREG);
- if (r < 0)
- return r;
- }
- fdt = open(f, O_CREAT|O_EXCL|O_NOFOLLOW|O_NOCTTY|O_WRONLY|O_CLOEXEC, 0600);
- if (copy_flags & COPY_MAC_CREATE)
- mac_selinux_create_file_clear();
- if (fdt < 0)
- return -errno;
-
- t = TAKE_PTR(f);
- } else {
- if (copy_flags & COPY_MAC_CREATE) {
- r = mac_selinux_create_file_prepare(to, S_IFREG);
- if (r < 0)
- return r;
- }
- fdt = open_tmpfile_linkable(to, O_WRONLY|O_CLOEXEC, &t);
- if (copy_flags & COPY_MAC_CREATE)
- mac_selinux_create_file_clear();
- if (fdt < 0)
- return fdt;
}
+ fdt = open_tmpfile_linkable(to, O_WRONLY|O_CLOEXEC, &t);
+ if (copy_flags & COPY_MAC_CREATE)
+ mac_selinux_create_file_clear();
+ if (fdt < 0)
+ return fdt;
if (chattr_mask != 0)
(void) chattr_fd(fdt, chattr_flags, chattr_mask & CHATTR_EARLY_FL, NULL);
@@ -1506,14 +1479,9 @@ int copy_file_atomic_full(
return -errno;
}
- if (copy_flags & COPY_REPLACE) {
- if (renameat(AT_FDCWD, t, AT_FDCWD, to) < 0)
- return -errno;
- } else {
- r = link_tmpfile(fdt, t, to);
- if (r < 0)
- return r;
- }
+ r = link_tmpfile(fdt, t, to, copy_flags & COPY_REPLACE);
+ if (r < 0)
+ return r;
t = mfree(t);
diff --git a/src/test/test-tmpfiles.c b/src/test/test-tmpfiles.c
index 83d11f5cf6..0a856200c7 100644
--- a/src/test/test-tmpfiles.c
+++ b/src/test/test-tmpfiles.c
@@ -52,12 +52,28 @@ TEST(tmpfiles) {
assert_se(write(fd, "foobar\n", 7) == 7);
assert_se(touch(d) >= 0);
- assert_se(link_tmpfile(fd, tmp, d) == -EEXIST);
+ assert_se(link_tmpfile(fd, tmp, d, /* replace= */ false) == -EEXIST);
assert_se(unlink(d) >= 0);
- assert_se(link_tmpfile(fd, tmp, d) >= 0);
+ assert_se(link_tmpfile(fd, tmp, d, /* replace= */ false) >= 0);
assert_se(read_one_line_file(d, &line) >= 0);
assert_se(streq(line, "foobar"));
+
+ fd = safe_close(fd);
+ tmp = mfree(tmp);
+
+ fd = open_tmpfile_linkable(d, O_RDWR|O_CLOEXEC, &tmp);
+ assert_se(fd >= 0);
+
+ assert_se(write(fd, "waumiau\n", 8) == 8);
+
+ assert_se(link_tmpfile(fd, tmp, d, /* replace= */ false) == -EEXIST);
+ assert_se(link_tmpfile(fd, tmp, d, /* replace= */ true) >= 0);
+
+ line = mfree(line);
+ assert_se(read_one_line_file(d, &line) >= 0);
+ assert_se(streq(line, "waumiau"));
+
assert_se(unlink(d) >= 0);
}
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