path: Skip directories when finalising $PATH search

Imagine $PATH /a:/b. There is an echo command at /b/echo. Under this
configuration, this works fine:

    % systemd-run --user --scope echo .
    Running scope as unit: run-rfe98e0574b424d63a641644af511ff30.scope
    .

However, if I do `mkdir /a/echo`, this happens:

    % systemd-run --user --scope echo .
    Running scope as unit: run-rcbe9369537ed47f282ee12ce9f692046.scope
    Failed to execute: Permission denied

We check whether the resulting file is executable for the performing
user, but of course, most directories are anyway, since that's needed to
list within it. As such, another is_dir() check is needed prior to
considering the search result final.

Another approach might be to check S_ISREG, but there may be more gnarly
edge cases there than just eliminating this obviously pathological
example, so let's just do this for now.

(cherry picked from commit 8b5cb69bc8b70d1dcc39ed2165907723099bd9d8)

diff --git a/src/basic/path-util.c b/src/basic/path-util.c
index c4e022b3a1187806635f771c7825322b42e4913c..d3b4978239475c656850fca3aae4c81021cb3be0 100644 (file)
--- a/src/basic/path-util.c
+++ b/src/basic/path-util.c
@@ -637,6 +637,9 @@ int find_binary(const char *name, char **ret) {
                 if (!j)
                         return -ENOMEM;
 
+                if (is_dir(j, true))
+                        continue;
+
                 if (access(j, X_OK) >= 0) {
                         /* Found it! */