Currently there does not exist a way to specify a path relative to which
all binaries executed by Exec should be found. The only way is to
specify the absolute path.
This change implements the functionality to specify a path relative to which
binaries executed by Exec*= can be found.
Closes#6308
When the root parameter in find_executable_full is set, chase_symlinks prefixes this root
to every check of the path name to find the complete path of the execuatble in case the
path provided is not absolute. This is only done for the non NULL root because otherwise
the chase_symlinks function would alter the behavior of some of the callers which would
in turn alter the outputs in a way that is undesirable. The find_execuatble_full function is
invoked by the verify_executable function in analyze-verify.
The two are completely identical, only the return code is inverted.
let's hence make it easy for the compiler to make it the same function
call even in lowest optimization modes.
I always found this a bit annoying.
With the patch:
$ SYSTEMD_LOG_LEVEL=debug build/udevadm test /sys/class/block/dm-1
...
Loaded timestamp for '/etc/systemd/network'.
Loaded timestamp for '/usr/lib/systemd/network'.
Parsed configuration file /usr/lib/systemd/network/99-default.link
Parsed configuration file /etc/systemd/network/10-eth0.link
Created link configuration context.
Loaded timestamp for '/etc/udev/rules.d'.
Loaded timestamp for '/usr/lib/udev/rules.d'.
...
This makes the functions handle "xx/" and "xx/." as equivalent.
Moreover, now path_extract_directory() returns normalized path, that is
no redundant "/" or "/./" are contained.
This also makes path_compare() may return arbitrary integer as it now
simply pass the result of strcmp() or memcmp().
This changes the behavior of path_extract_filename/directory() when
e.g. "/." or "/./" are input. But the change should be desired.
Let's fine-tune the path_extract_filename() interface: on succes return
O_DIRECTORY as indicator that the input path was slash-suffixed, and
regular 0 otherwise. This is useful since in many cases it is useful to
filter out paths that must refer to dirs early on.
I opted for O_DIRECTORY instead of the following other ideas:
1. return -EISDIR: I think the function should return an extracted
filename even when referring to an obvious dir, so this is not an
option.
2. S_ISDIR, this was a strong contender, but I think O_DIRECTORY is a
tiny bit nicer since quite likely we will go on and open the thing,
maybe with openat(), and hence it's quite nice to be able to OR in
the return value into the flags argument of openat().
3. A new enum defined with two values "dont-know" and
"definitely-directory". But I figured this was unnecessary, given we
have other options too, that reuse existing definitions for very
similar purposes.
These two together are a lot like dirname() + basename() but have the
benefit that they return clear errors when one passes a special case
path to them where the extraction doesn't make sense, i.e. "", "/",
"foo", "foo/" and so on.
Sooner or later we should probably port all our uses of
dirname()/basename() over to this, to catch these special cases more
safely.
Let's tighten the logic behind path_extract_filename() a bit: first of
all, refuse all cases of invalid paths with -EINVAL. More importantly
though return a recognizable error when a valid path is specified that
does not contain any filename. Specifically, "/" will now result in
-EADDRNOTAVAIL.
This changes API, but none of the existing callers care about the return
value, hence the change should be fine.
Follow-up for ece852c845.
This addresses the following comments by the Lennart:
---
hmm, so this now does two access() calls for the case where the fd is
not requested, and opens things up for races (theoretically, …). now,
the access() code path was in place for optimization, but if an optimization
is less sexy than the original (and i think it is less sexy, since more
than one syscall, and non-atomic), i think we shouldn't do the optimization.
maybe we should just always use open(O_PATH) now, and then fstat() it to
check if regular file, and then access_fd() it for checking if its executable.
Previously:
1. last_error wouldn't be updated with errors from is_dir;
2. We'd always issue a stat(), even for binaries without execute;
3. We used stat() instead of access(), which is cheaper.
This change avoids all of those, by only checking inside X_OK-positive
case whether access() works on the path with an extra slash appended.
Thanks to Lennart for the suggestion.
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.
It annoyed me for quite a while that running "journalctl --file=…" on a
file that is not readable failed with a "File not found" error instead
of a permission error. Let's fix that.
We make this work by using the GLOB_NOCHECK flag for glob() which means
that files are not accessible will be returned in the array as they are
instead of being filtered away. This then means that our later attemps
to open the files will fail cleanly with a good error message.
Lennart Poettering
alexlzhu
Yu Watanabe
Maanya Goenka
Zbigniew Jędrzejewski-Szmek
Luca Boccassi
Chris Down
Topi Miettinen