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user-util: stop mangling groupname in get_group_creds

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The param was input/output, which is unexpected and confusing and
actually made most callers much more complicated than they needed to be.
The function was playing fast and loose with the return value. In some
cases it was returning a static string, which would be completely fine.
But in other case it was returning a pointer into the getgrgid static
buffer, i.e. that return value could be overwritten. AFAICT, this didn't
matter in any of the callers, but we shouldn't do that anyway.

So use a separate output param with an allocated string that the caller
is responsible for.

It turns out that all callers pass NULL (outside of tests) and zero for
flags. So the function _could_ be simplified. But get_user_creds is
called with all the params actually used, and I think having the the
functions so different wouldn't be nice. I first wrote a commit to
drop the unused params, but then I discarded it.

The error message in exec-invoke.c is fixed.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2026-05-21 18:02:05 +02:00
parent 3d0a05dcc3
commit 3ecd6b69cf
8 changed files with 64 additions and 105 deletions
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src/run/run.c
+4 -5
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@@ -2571,7 +2571,7 @@ static int start_transient_scope(sd_bus *bus) {
if (arg_exec_group) {
gid_t gid;
r = get_group_creds(&arg_exec_group, &gid, 0);
r = get_group_creds(arg_exec_group, /* flags= */ 0, /* ret_name= */ NULL, &gid);
if (r < 0)
return log_error_errno(r, "Failed to resolve group '%s': %s",
arg_exec_group, STRERROR_GROUP(r));
@@ -2615,10 +2615,9 @@ static int start_transient_scope(sd_bus *bus) {
if (r < 0)
return log_oom();
if (!arg_exec_group) {
if (setresgid(gid, gid, gid) < 0)
return log_error_errno(errno, "Failed to change GID to " GID_FMT ": %m", gid);
}
if (!arg_exec_group &&
setresgid(gid, gid, gid) < 0)
return log_error_errno(errno, "Failed to change GID to " GID_FMT ": %m", gid);
if (setresuid(uid, uid, uid) < 0)
return log_error_errno(errno, "Failed to change UID to " UID_FMT ": %m", uid);