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util-lib: optionally, when writing a string to a file, verify string on failure 

With this change, the idiom:

    r = write_string_file(p, buf, 0);
    if (r < 0) {
           if (verify_one_line_file(p, buf) > 0)
                   r = 0;
    }

gets reduced to:

    r = write_string_file(p, buf, WRITE_STRING_FILE_VERIFY_ON_FAILURE);

i.e. when writing the string fails and the new flag
WRITE_STRING_FILE_VERIFY_ON_FAILURE is specified we'll not return a
failure immediately, but check the contents of the file. If it matches
what we wanted to write we suppress the error and exit cleanly.
This commit is contained in:
Lennart Poettering 2015-11-13 00:54:56 +01:00
parent 87fde73e18
commit eb3da9012f
4 changed files with 104 additions and 57 deletions
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83
src/basic/fileio.c
View File

@ -78,6 +78,7 @@ static int write_string_file_atomic(const char *fn, const char *line, bool enfor
int write_string_file(const char *fn, const char *line, WriteStringFileFlags flags) {
_cleanup_fclose_ FILE *f = NULL;
int q, r;
assert(fn);
assert(line);
@ -85,30 +86,58 @@ int write_string_file(const char *fn, const char *line, WriteStringFileFlags fla
if (flags & WRITE_STRING_FILE_ATOMIC) {
assert(flags & WRITE_STRING_FILE_CREATE);
return write_string_file_atomic(fn, line, !(flags & WRITE_STRING_FILE_AVOID_NEWLINE));
r = write_string_file_atomic(fn, line, !(flags & WRITE_STRING_FILE_AVOID_NEWLINE));
if (r < 0)
goto fail;
return r;
}
if (flags & WRITE_STRING_FILE_CREATE) {
f = fopen(fn, "we");
if (!f)
return -errno;
if (!f) {
r = -errno;
goto fail;
}
} else {
int fd;
/* We manually build our own version of fopen(..., "we") that
* works without O_CREAT */
fd = open(fn, O_WRONLY|O_CLOEXEC|O_NOCTTY);
if (fd < 0)
return -errno;
if (fd < 0) {
r = -errno;
goto fail;
}
f = fdopen(fd, "we");
if (!f) {
r = -errno;
safe_close(fd);
return -errno;
goto fail;
}
}
return write_string_stream(f, line, !(flags & WRITE_STRING_FILE_AVOID_NEWLINE));
r = write_string_stream(f, line, !(flags & WRITE_STRING_FILE_AVOID_NEWLINE));
if (r < 0)
goto fail;
return 0;
fail:
if (!(flags & WRITE_STRING_FILE_VERIFY_ON_FAILURE))
return r;
f = safe_fclose(f);
/* OK, the operation failed, but let's see if the right
* contents in place already. If so, eat up the error. */
q = verify_file(fn, line, !(flags & WRITE_STRING_FILE_AVOID_NEWLINE));
if (q <= 0)
return r;
return 0;
}
int read_one_line_file(const char *fn, char **line) {
@ -139,15 +168,41 @@ int read_one_line_file(const char *fn, char **line) {
return 0;
}
int verify_one_line_file(const char *fn, const char *line) {
_cleanup_free_ char *value = NULL;
int r;
int verify_file(const char *fn, const char *blob, bool accept_extra_nl) {
_cleanup_fclose_ FILE *f = NULL;
_cleanup_free_ char *buf = NULL;
size_t l, k;
r = read_one_line_file(fn, &value);
if (r < 0)
return r;
assert(fn);
assert(blob);
return streq(value, line);
l = strlen(blob);
if (accept_extra_nl && endswith(blob, "\n"))
accept_extra_nl = false;
buf = malloc(l + accept_extra_nl + 1);
if (!buf)
return -ENOMEM;
f = fopen(fn, "re");
if (!f)
return -errno;
/* We try to read one byte more than we need, so that we know whether we hit eof */
errno = 0;
k = fread(buf, 1, l + accept_extra_nl + 1, f);
if (ferror(f))
return errno > 0 ? -errno : -EIO;
if (k != l && k != l + accept_extra_nl)
return 0;
if (memcmp(buf, blob, l) != 0)
return 0;
if (k > l && buf[l] != '\n')
return 0;
return 1;
}
int read_full_stream(FILE *f, char **contents, size_t *size) {

3
src/basic/fileio.h
View File

@ -34,6 +34,7 @@ typedef enum {
WRITE_STRING_FILE_CREATE = 1,
WRITE_STRING_FILE_ATOMIC = 2,
WRITE_STRING_FILE_AVOID_NEWLINE = 4,
WRITE_STRING_FILE_VERIFY_ON_FAILURE = 8,
} WriteStringFileFlags;
int write_string_stream(FILE *f, const char *line, bool enforce_newline);
@ -43,7 +44,7 @@ int read_one_line_file(const char *fn, char **line);
int read_full_file(const char *fn, char **contents, size_t *size);
int read_full_stream(FILE *f, char **contents, size_t *size);
int verify_one_line_file(const char *fn, const char *line);
int verify_file(const char *fn, const char *blob, bool accept_extra_nl);
int parse_env_file(const char *fname, const char *separator, ...) _sentinel_;
int load_env_file(FILE *f, const char *fname, const char *separator, char ***l);

54
src/network/networkd-link.c
View File

@ -1859,14 +1859,9 @@ static int link_set_ipv4_forward(Link *link) {
p = strjoina("/proc/sys/net/ipv4/conf/", link->ifname, "/forwarding");
v = one_zero(link_ipv4_forward_enabled(link));
r = write_string_file(p, v, 0);
if (r < 0) {
/* If the right value is set anyway, don't complain */
if (verify_one_line_file(p, v) > 0)
return 0;
r = write_string_file(p, v, WRITE_STRING_FILE_VERIFY_ON_FAILURE);
if (r < 0)
log_link_warning_errno(link, r, "Cannot configure IPv4 forwarding for interface %s: %m", link->ifname);
}
return 0;
}
@ -1888,14 +1883,9 @@ static int link_set_ipv6_forward(Link *link) {
p = strjoina("/proc/sys/net/ipv6/conf/", link->ifname, "/forwarding");
v = one_zero(link_ipv6_forward_enabled(link));
r = write_string_file(p, v, 0);
if (r < 0) {
/* If the right value is set anyway, don't complain */
if (verify_one_line_file(p, v) > 0)
return 0;
r = write_string_file(p, v, WRITE_STRING_FILE_VERIFY_ON_FAILURE);
if (r < 0)
log_link_warning_errno(link, r, "Cannot configure IPv6 forwarding for interface: %m");
}
return 0;
}
@ -1917,14 +1907,9 @@ static int link_set_ipv6_privacy_extensions(Link *link) {
p = strjoina("/proc/sys/net/ipv6/conf/", link->ifname, "/use_tempaddr");
xsprintf(buf, "%u", link->network->ipv6_privacy_extensions);
r = write_string_file(p, buf, 0);
if (r < 0) {
/* If the right value is set anyway, don't complain */
if (verify_one_line_file(p, buf) > 0)
return 0;
r = write_string_file(p, buf, WRITE_STRING_FILE_VERIFY_ON_FAILURE);
if (r < 0)
log_link_warning_errno(link, r, "Cannot configure IPv6 privacy extension for interface: %m");
}
return 0;
}
@ -1943,14 +1928,9 @@ static int link_set_ipv6_accept_ra(Link *link) {
p = strjoina("/proc/sys/net/ipv6/conf/", link->ifname, "/accept_ra");
/* we handle router advertisments ourselves, tell the kernel to GTFO */
r = write_string_file(p, "0", 0);
if (r < 0) {
/* If the right value is set anyway, don't complain */
if (verify_one_line_file(p, "0") > 0)
return 0;
r = write_string_file(p, "0", WRITE_STRING_FILE_VERIFY_ON_FAILURE);
if (r < 0)
log_link_warning_errno(link, r, "Cannot disable kernel IPv6 accept_ra for interface: %m");
}
return 0;
}
@ -1974,14 +1954,9 @@ static int link_set_ipv6_dad_transmits(Link *link) {
xsprintf(buf, "%u", link->network->ipv6_dad_transmits);
r = write_string_file(p, buf, 0);
if (r < 0) {
/* If the right value is set anyway, don't complain */
if (verify_one_line_file(p, buf) > 0)
return 0;
r = write_string_file(p, buf, WRITE_STRING_FILE_VERIFY_ON_FAILURE);
if (r < 0)
log_link_warning_errno(link, r, "Cannot set IPv6 dad transmits for interface: %m");
}
return 0;
}
@ -2005,14 +1980,9 @@ static int link_set_ipv6_hop_limit(Link *link) {
xsprintf(buf, "%u", link->network->ipv6_hop_limit);
r = write_string_file(p, buf, 0);
if (r < 0) {
/* If the right value is set anyway, don't complain */
if (verify_one_line_file(p, buf) > 0)
return 0;
r = write_string_file(p, buf, WRITE_STRING_FILE_VERIFY_ON_FAILURE);
if (r < 0)
log_link_warning_errno(link, r, "Cannot set IPv6 hop limit for interface: %m");
}
return 0;
}

21
src/test/test-fileio.c
View File

@ -363,6 +363,26 @@ static void test_write_string_file_no_create(void) {
unlink(fn);
}
static void test_write_string_file_verify(void) {
_cleanup_free_ char *buf = NULL, *buf2 = NULL;
int r;
assert_se(read_one_line_file("/proc/cmdline", &buf) >= 0);
assert_se((buf2 = strjoin(buf, "\n", NULL)));
r = write_string_file("/proc/cmdline", buf, 0);
assert_se(r == -EACCES || r == -EIO);
r = write_string_file("/proc/cmdline", buf2, 0);
assert_se(r == -EACCES || r == -EIO);
assert_se(write_string_file("/proc/cmdline", buf, WRITE_STRING_FILE_VERIFY_ON_FAILURE) == 0);
assert_se(write_string_file("/proc/cmdline", buf2, WRITE_STRING_FILE_VERIFY_ON_FAILURE) == 0);
r = write_string_file("/proc/cmdline", buf, WRITE_STRING_FILE_VERIFY_ON_FAILURE|WRITE_STRING_FILE_AVOID_NEWLINE);
assert_se(r == -EACCES || r == -EIO);
assert_se(write_string_file("/proc/cmdline", buf2, WRITE_STRING_FILE_VERIFY_ON_FAILURE|WRITE_STRING_FILE_AVOID_NEWLINE) == 0);
}
static void test_load_env_file_pairs(void) {
char fn[] = "/tmp/test-load_env_file_pairs-XXXXXX";
int fd;
@ -419,6 +439,7 @@ int main(int argc, char *argv[]) {
test_write_string_stream();
test_write_string_file();
test_write_string_file_no_create();
test_write_string_file_verify();
test_load_env_file_pairs();
return 0;