tree-wide: check memstream buffer after closing the handle

When closing the FILE handle attached to a memstream, it may attempt to
do a realloc() that may fail during OOM situations, in which case we are
left with the buffer pointer pointing to NULL and buffer size > 0. For
example:

```
    #include <errno.h>
    #include <stdio.h>
    #include <stdlib.h>

    void *realloc(void *ptr, size_t size) {
        return NULL;
    }

    int main(int argc, char *argv[])
    {
        FILE *f;
        char *buf;
        size_t sz = 0;

        f = open_memstream(&buf, &sz);
        if (!f)
            return -ENOMEM;

        fputs("Hello", f);

        fflush(f);
        printf("buf: 0x%lx, sz: %lu, errno: %d\n",
                    (unsigned long) buf, sz, errno);
        fclose(f);
        printf("buf: 0x%lx, sz: %lu, errno: %d\n",
                    (unsigned long) buf, sz, errno);

        return 0;
    }
```

```
$ gcc -o main main.c
$ ./main
buf: 0x74d4a0, sz: 5, errno: 0
buf: 0x0, sz: 5, errno: 0
```

This might do unexpected things if the underlying code expects a valid
pointer to the memstream buffer after closing the handle.

Found by Nallocfuzz.

src/basic/string-util.c

@@ -9,6 +9,7 @@
 #include "alloc-util.h"
 #include "escape.h"
 #include "extract-word.h"
+#include "fd-util.h"
 #include "fileio.h"
 #include "gunicode.h"
 #include "locale-util.h"
@@ -603,9 +604,9 @@ char *strip_tab_ansi(char **ibuf, size_t *_isz, size_t highlight[2]) {
                 STATE_CSI,
                 STATE_CSO,
         } state = STATE_OTHER;
-        char *obuf = NULL;
+        _cleanup_free_ char *obuf = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
         size_t osz = 0, isz, shift[2] = {}, n_carriage_returns = 0;
-        FILE *f;
 
         assert(ibuf);
         assert(*ibuf);
@@ -713,11 +714,13 @@ char *strip_tab_ansi(char **ibuf, size_t *_isz, size_t highlight[2]) {
                 }
         }
 
-        if (fflush_and_check(f) < 0) {
-                fclose(f);
-                return mfree(obuf);
-        }
-        fclose(f);
+        if (fflush_and_check(f) < 0)
+                return NULL;
+
+        f = safe_fclose(f);
+
+        if (!obuf)
+                return NULL;
 
         free_and_replace(*ibuf, obuf);
 

src/busctl/busctl.c

@@ -1072,6 +1072,9 @@ static int introspect(int argc, char **argv, void *userdata) {
 
                         mf = safe_fclose(mf);
 
+                        if (!buf)
+                                return bus_log_parse_error(ENOMEM);
+
                         z = set_get(members, &((Member) {
                                                 .type = "property",
                                                 .interface = m->interface,

src/core/manager-dump.c

@@ -95,6 +95,9 @@ int manager_get_dump_string(Manager *m, char **patterns, char **ret) {
 
         f = safe_fclose(f);
 
+        if (!dump)
+                return -ENOMEM;
+
         *ret = TAKE_PTR(dump);
 
         return 0;

src/coredump/coredump.c

@@ -707,6 +707,9 @@ static int compose_open_fds(pid_t pid, char **open_fds) {
         if (errno > 0)
                 return -errno;
 
+        if (!buffer)
+                return -ENOMEM;
+
         *open_fds = TAKE_PTR(buffer);
 
         return 0;

src/journal/journalctl.c

@@ -1811,6 +1811,10 @@ static int format_journal_url(
                 return r;
 
         f = safe_fclose(f);
+
+        if (!url)
+                return -ENOMEM;
+
         *ret_url = TAKE_PTR(url);
         return 0;
 }

src/libsystemd/sd-bus/bus-introspect.c

@@ -268,6 +268,10 @@ int introspect_finish(struct introspect *i, char **ret) {
                 return r;
 
         i->f = safe_fclose(i->f);
+
+        if (!i->introspection)
+                return -ENOMEM;
+
         *ret = TAKE_PTR(i->introspection);
 
         return 0;

src/libsystemd/sd-bus/bus-match.c

@@ -824,6 +824,7 @@ int bus_match_parse(
 
 char *bus_match_to_string(struct bus_match_component *components, size_t n_components) {
         _cleanup_free_ char *buffer = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
         size_t size = 0;
         int r;
 
@@ -832,7 +833,7 @@ char *bus_match_to_string(struct bus_match_component *components, size_t n_compo
 
         assert(components);
 
-        FILE *f = open_memstream_unlocked(&buffer, &size);
+        f = open_memstream_unlocked(&buffer, &size);
         if (!f)
                 return NULL;
 
@@ -855,9 +856,11 @@ char *bus_match_to_string(struct bus_match_component *components, size_t n_compo
         }
 
         r = fflush_and_check(f);
-        safe_fclose(f);
         if (r < 0)
                 return NULL;
+
+        f = safe_fclose(f);
+
         return TAKE_PTR(buffer);
 }
 

src/network/generator/network-generator.c

@@ -1199,30 +1199,31 @@ void link_dump(Link *link, FILE *f) {
 
 int network_format(Network *network, char **ret) {
         _cleanup_free_ char *s = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
         size_t sz = 0;
         int r;
 
         assert(network);
         assert(ret);
 
-        {
-                _cleanup_fclose_ FILE *f = NULL;
+        f = open_memstream_unlocked(&s, &sz);
+        if (!f)
+                return -ENOMEM;
 
-                f = open_memstream_unlocked(&s, &sz);
-                if (!f)
-                        return -ENOMEM;
+        network_dump(network, f);
 
-                network_dump(network, f);
+        /* Add terminating 0, so that the output buffer is a valid string. */
+        fputc('\0', f);
 
-                /* Add terminating 0, so that the output buffer is a valid string. */
-                fputc('\0', f);
-
-                r = fflush_and_check(f);
-        }
+        r = fflush_and_check(f);
         if (r < 0)
                 return r;
 
-        assert(s);
+        f = safe_fclose(f);
+
+        if (!s)
+                return -ENOMEM;
+
         *ret = TAKE_PTR(s);
         assert(sz > 0);
         return (int) sz - 1;
@@ -1230,30 +1231,31 @@ int network_format(Network *network, char **ret) {
 
 int netdev_format(NetDev *netdev, char **ret) {
         _cleanup_free_ char *s = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
         size_t sz = 0;
         int r;
 
         assert(netdev);
         assert(ret);
 
-        {
-                _cleanup_fclose_ FILE *f = NULL;
+        f = open_memstream_unlocked(&s, &sz);
+        if (!f)
+                return -ENOMEM;
 
-                f = open_memstream_unlocked(&s, &sz);
-                if (!f)
-                        return -ENOMEM;
+        netdev_dump(netdev, f);
 
-                netdev_dump(netdev, f);
+        /* Add terminating 0, so that the output buffer is a valid string. */
+        fputc('\0', f);
 
-                /* Add terminating 0, so that the output buffer is a valid string. */
-                fputc('\0', f);
-
-                r = fflush_and_check(f);
-        }
+        r = fflush_and_check(f);
         if (r < 0)
                 return r;
 
-        assert(s);
+        f = safe_fclose(f);
+
+        if (!s)
+                return -ENOMEM;
+
         *ret = TAKE_PTR(s);
         assert(sz > 0);
         return (int) sz - 1;
@@ -1261,30 +1263,31 @@ int netdev_format(NetDev *netdev, char **ret) {
 
 int link_format(Link *link, char **ret) {
         _cleanup_free_ char *s = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
         size_t sz = 0;
         int r;
 
         assert(link);
         assert(ret);
 
-        {
-                _cleanup_fclose_ FILE *f = NULL;
+        f = open_memstream_unlocked(&s, &sz);
+        if (!f)
+                return -ENOMEM;
 
-                f = open_memstream_unlocked(&s, &sz);
-                if (!f)
-                        return -ENOMEM;
+        link_dump(link, f);
 
-                link_dump(link, f);
+        /* Add terminating 0, so that the output buffer is a valid string. */
+        fputc('\0', f);
 
-                /* Add terminating 0, so that the output buffer is a valid string. */
-                fputc('\0', f);
-
-                r = fflush_and_check(f);
-        }
+        r = fflush_and_check(f);
         if (r < 0)
                 return r;
 
-        assert(s);
+        f = safe_fclose(f);
+
+        if (!s)
+                return -ENOMEM;
+
         *ret = TAKE_PTR(s);
         assert(sz > 0);
         return (int) sz - 1;

src/oom/oomd-manager.c

@@ -847,6 +847,9 @@ int manager_get_dump_string(Manager *m, char **ret) {
 
         f = safe_fclose(f);
 
+        if (!dump)
+                return -ENOMEM;
+
         *ret = TAKE_PTR(dump);
         return 0;
 }

src/oom/oomd-util.c

@@ -299,6 +299,11 @@ static int dump_kill_candidates(OomdCGroupContext **sorted, int n, int dump_unti
         if (r < 0)
                 return r;
 
+        f = safe_fclose(f);
+
+        if (!dump)
+                return -ENOMEM;
+
         return log_dump(LOG_INFO, dump);
 }
 

src/resolve/resolved-dns-dnssec.c

@@ -867,10 +867,14 @@ static int dnssec_rrset_serialize_sig(
         }
 
         r = fflush_and_check(f);
-        f = safe_fclose(f);  /* sig_data may be reallocated when f is closed. */
         if (r < 0)
                 return r;
 
+        f = safe_fclose(f);  /* sig_data may be reallocated when f is closed. */
+
+        if (!sig_data)
+                return -ENOMEM;
+
         *ret_sig_data = TAKE_PTR(sig_data);
         *ret_sig_size = sig_size;
         return 0;

src/resolve/resolved-manager.c

@@ -519,6 +519,11 @@ static int manager_sigusr1(sd_event_source *s, const struct signalfd_siginfo *si
         if (fflush_and_check(f) < 0)
                 return log_oom();
 
+        f = safe_fclose(f);
+
+        if (!buffer)
+                return -ENOMEM;
+
         log_dump(LOG_INFO, buffer);
         return 0;
 }

src/shared/bus-util.c

@@ -628,6 +628,9 @@ static int method_dump_memory_state_by_fd(sd_bus_message *message, void *userdat
 
         dump_file = safe_fclose(dump_file);
 
+        if (!dump)
+                return -ENOMEM;
+
         fd = acquire_data_fd(dump, dump_size, 0);
         if (fd < 0)
                 return fd;

src/shared/calendarspec.c

@@ -12,6 +12,7 @@
 #include "alloc-util.h"
 #include "calendarspec.h"
 #include "errno-util.h"
+#include "fd-util.h"
 #include "fileio.h"
 #include "macro.h"
 #include "parse-util.h"
@@ -337,9 +338,9 @@ static void format_chain(FILE *f, int space, const CalendarComponent *c, bool us
 }
 
 int calendar_spec_to_string(const CalendarSpec *c, char **p) {
-        char *buf = NULL;
+        _cleanup_free_ char *buf = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
         size_t sz = 0;
-        FILE *f;
         int r;
 
         assert(c);
@@ -384,14 +385,15 @@ int calendar_spec_to_string(const CalendarSpec *c, char **p) {
         }
 
         r = fflush_and_check(f);
-        fclose(f);
-
-        if (r < 0) {
-                free(buf);
+        if (r < 0)
                 return r;
-        }
 
-        *p = buf;
+        f = safe_fclose(f);
+
+        if (!buf)
+                return -ENOMEM;
+
+        *p = TAKE_PTR(buf);
         return 0;
 }
 

src/shared/elf-util.c

@@ -621,8 +621,13 @@ static int parse_core(int fd, const char *executable, char **ret, JsonVariant **
                         return log_warning_errno(r, "Could not parse core file, flushing file buffer failed: %m");
 
                 c.f = safe_fclose(c.f);
+
+                if (!buf)
+                        return log_oom();
+
                 *ret = TAKE_PTR(buf);
         }
+
         if (ret_package_metadata)
                 *ret_package_metadata = TAKE_PTR(package_metadata);
 
@@ -735,8 +740,13 @@ static int parse_elf(int fd, const char *executable, char **ret, JsonVariant **r
                         return log_warning_errno(r, "Could not parse ELF file, flushing file buffer failed: %m");
 
                 c.f = safe_fclose(c.f);
+
+                if (!buf)
+                        return log_oom();
+
                 *ret = TAKE_PTR(buf);
         }
+
         if (ret_package_metadata)
                 *ret_package_metadata = TAKE_PTR(elf_metadata);
 

src/shared/format-table.c

@@ -2537,6 +2537,9 @@ int table_format(Table *t, char **ret) {
 
         f = safe_fclose(f);
 
+        if (!buf)
+                return -ENOMEM;
+
         *ret = TAKE_PTR(buf);
 
         return 0;

src/shared/json.c

@@ -1769,6 +1769,7 @@ static int json_format(FILE *f, JsonVariant *v, JsonFormatFlags flags, const cha
 
 int json_variant_format(JsonVariant *v, JsonFormatFlags flags, char **ret) {
         _cleanup_free_ char *s = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
         size_t sz = 0;
         int r;
 
@@ -1781,26 +1782,26 @@ int json_variant_format(JsonVariant *v, JsonFormatFlags flags, char **ret) {
         if (flags & JSON_FORMAT_OFF)
                 return -ENOEXEC;
 
-        {
-                _cleanup_fclose_ FILE *f = NULL;
+        f = open_memstream_unlocked(&s, &sz);
+        if (!f)
+                return -ENOMEM;
 
-                f = open_memstream_unlocked(&s, &sz);
-                if (!f)
-                        return -ENOMEM;
-
-                r = json_variant_dump(v, flags, f, NULL);
-                if (r < 0)
-                        return r;
-
-                /* Add terminating 0, so that the output buffer is a valid string. */
-                fputc('\0', f);
-
-                r = fflush_and_check(f);
-        }
+        r = json_variant_dump(v, flags, f, NULL);
         if (r < 0)
                 return r;
 
-        assert(s);
+        /* Add terminating 0, so that the output buffer is a valid string. */
+        fputc('\0', f);
+
+        r = fflush_and_check(f);
+        if (r < 0)
+                return r;
+
+        f = safe_fclose(f);
+
+        if (!s)
+                return -ENOMEM;
+
         *ret = TAKE_PTR(s);
         assert(sz > 0);
         return (int) sz - 1;