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util: rework fgetxattrat_fake() to use O_PATH

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That way, we don't ever open the file, thus leave the atime untouched,
and this works even when unprivileged.
This commit is contained in:
Lennart Poettering 2015-10-02 11:43:19 +02:00
parent e46831f0f1
commit df241a67c0
2 changed files with 40 additions and 2 deletions
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7
src/basic/util.c
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@ -6168,16 +6168,19 @@ int openpt_in_namespace(pid_t pid, int flags) {
}
ssize_t fgetxattrat_fake(int dirfd, const char *filename, const char *attribute, void *value, size_t size, int flags) {
char fn[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
_cleanup_close_ int fd = -1;
ssize_t l;
/* The kernel doesn't have a fgetxattrat() command, hence let's emulate one */
fd = openat(dirfd, filename, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOATIME|(flags & AT_SYMLINK_NOFOLLOW ? O_NOFOLLOW : 0));
fd = openat(dirfd, filename, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_PATH|(flags & AT_SYMLINK_NOFOLLOW ? O_NOFOLLOW : 0));
if (fd < 0)
return -errno;
l = fgetxattr(fd, attribute, value, size);
xsprintf(fn, "/proc/self/fd/%i", fd);
l = getxattr(fn, attribute, value, size);
if (l < 0)
return -errno;

35
src/test/test-util.c
View file

@ -26,7 +26,9 @@
#include <math.h>
#include <signal.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/xattr.h>
#include <unistd.h>
#include "conf-parser.h"
@ -2263,6 +2265,38 @@ static void test_strcmp_ptr(void) {
assert_se(strcmp_ptr("", "") == 0);
}
static void test_fgetxattrat_fake(void) {
char t[] = "/var/tmp/xattrtestXXXXXX";
_cleanup_close_ int fd = -1;
const char *x;
char v[3] = {};
int r;
assert_se(mkdtemp(t));
x = strjoina(t, "/test");
assert_se(touch(x) >= 0);
r = setxattr(x, "user.foo", "bar", 3, 0);
if (r < 0 && errno == EOPNOTSUPP) /* no xattrs supported on /var/tmp... */
goto cleanup;
assert_se(r >= 0);
fd = open(t, O_RDONLY|O_DIRECTORY|O_CLOEXEC|O_NOCTTY);
assert_se(fd >= 0);
assert_se(fgetxattrat_fake(fd, "test", "user.foo", v, 3, 0) >= 0);
assert_se(memcmp(v, "bar", 3) == 0);
safe_close(fd);
fd = open("/", O_RDONLY|O_DIRECTORY|O_CLOEXEC|O_NOCTTY);
assert_se(fd >= 0);
assert_se(fgetxattrat_fake(fd, "usr", "user.idontexist", v, 3, 0) == -ENODATA);
cleanup:
assert_se(unlink(x) >= 0);
assert_se(rmdir(t) >= 0);
}
int main(int argc, char *argv[]) {
log_parse_environment();
log_open();
@ -2353,6 +2387,7 @@ int main(int argc, char *argv[]) {
test_parse_mode();
test_tempfn();
test_strcmp_ptr();
test_fgetxattrat_fake();
return 0;
}