systemd-path: fix memory leak reported by ASAN (#8874)

The leak can be reproduced by running systemd-path --suffix .tmp under valgrind or asan:

    $ ./build/systemd-path --suffix .tmp search-binaries
    /usr/local/bin/.tmp:/usr/bin/.tmp:/usr/local/sbin/.tmp:/usr/sbin/.tmp:/home/vagrant/.local/bin/.tmp:/home/vagrant/bin/.tmp

    =================================================================
    ==19177==ERROR: LeakSanitizer: detected memory leaks

    Direct leak of 56 byte(s) in 1 object(s) allocated from:
        *0 0x7fd6adf72850 in malloc (/lib64/libasan.so.4+0xde850)
        *1 0x7fd6ad2b93d2 in malloc_multiply ../src/basic/alloc-util.h:69
        *2 0x7fd6ad2bafd2 in strv_split ../src/basic/strv.c:269
        *3 0x7fd6ad42ba67 in search_from_environment ../src/libsystemd/sd-path/sd-path.c:409
        *4 0x7fd6ad42bffe in get_search ../src/libsystemd/sd-path/sd-path.c:482
        *5 0x7fd6ad42c55b in sd_path_search ../src/libsystemd/sd-path/sd-path.c:607
        *6 0x7fd6ad42b3a2 in sd_path_home ../src/libsystemd/sd-path/sd-path.c:348
        *7 0x55f59c65ebea in print_home ../src/path/path.c:97
        *8 0x55f59c65f157 in main ../src/path/path.c:177
        *9 0x7fd6abaea009 in __libc_start_main (/lib64/libc.so.6+0x21009)

    Indirect leak of 68 byte(s) in 5 object(s) allocated from:
        *0 0x7fd6adf72850 in malloc (/lib64/libasan.so.4+0xde850)
        *1 0x7fd6abb5f689 in strndup (/lib64/libc.so.6+0x96689)

    Indirect leak of 25 byte(s) in 1 object(s) allocated from:
        *0 0x7fd6adf72850 in malloc (/lib64/libasan.so.4+0xde850)
        *1 0x7fd6abb5f689 in strndup (/lib64/libc.so.6+0x96689)
        *2 0x6c2e2f746e617266  (<unknown module>)

    SUMMARY: AddressSanitizer: 149 byte(s) leaked in 7 allocation(s).

1 files changed, 7 insertions, 11 deletions

diff --git a/src/libsystemd/sd-path/sd-path.c b/src/libsystemd/sd-path/sd-path.c
index c75a39613b..b1a1cdc4f4 100644
--- a/src/libsystemd/sd-path/sd-path.c
+++ b/src/libsystemd/sd-path/sd-path.c
@@ -570,7 +570,8 @@ static int get_search(uint64_t type, char ***list) {
 }
 
 _public_ int sd_path_search(uint64_t type, const char *suffix, char ***paths) {
-        char **l, **i, **j, **n;
+        char **i, **j;
+        _cleanup_strv_free_ char **l = NULL, **n = NULL;
         int r;
 
         assert_return(paths, -EINVAL);
@@ -600,7 +601,7 @@ _public_ int sd_path_search(uint64_t type, const char *suffix, char ***paths) {
                 l[0] = p;
                 l[1] = NULL;
 
-                *paths = l;
+                *paths = TAKE_PTR(l);
                 return 0;
         }
 
@@ -609,15 +610,13 @@ _public_ int sd_path_search(uint64_t type, const char *suffix, char ***paths) {
                 return r;
 
         if (!suffix) {
-                *paths = l;
+                *paths = TAKE_PTR(l);
                 return 0;
         }
 
         n = new(char*, strv_length(l)+1);
-        if (!n) {
-                strv_free(l);
+        if (!n)
                 return -ENOMEM;
-        }
 
         j = n;
         STRV_FOREACH(i, l) {
@@ -627,16 +626,13 @@ _public_ int sd_path_search(uint64_t type, const char *suffix, char ***paths) {
                 else
                         *j = strjoin(*i, "/", suffix);
 
-                if (!*j) {
-                        strv_free(l);
-                        strv_free(n);
+                if (!*j)
                         return -ENOMEM;
-                }
 
                 j++;
         }
 
         *j = NULL;
-        *paths = n;
+        *paths = TAKE_PTR(n);
         return 0;
 }