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sd-device: don't accept non-sysfs paths

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There are some file systems mounted below /sys/ that are not actually
sysfs, i.e. are not arranged in a sysfs/kobject style. Let's refuse
those early. (Example, /sys/fs/cgroup/ and similar.)

(Also, let's add an env var for this, so that it can be turned off for
test cases.)
This commit is contained in:
Lennart Poettering 2022-04-11 22:04:06 +02:00
parent 1793bb6112
commit a7910612a5
3 changed files with 26 additions and 1 deletions
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6
docs/ENVIRONMENT.md
View file

@ -199,7 +199,7 @@ All tools:
or whenever they change if it wants to integrate with `systemd-logind`'s
APIs.
`systemd-udevd`:
`systemd-udevd` and sd-device library:
* `$NET_NAMING_SCHEME=` — if set, takes a network naming scheme (i.e. one of
"v238", "v239", "v240"…, or the special value "latest") as parameter. If
@ -211,6 +211,10 @@ All tools:
prefixed with `:` in which case the kernel command line option takes
precedence, if it is specified as well.
* `$SYSTEMD_DEVICE_VERIFY_SYSFS` — if set to "0", disables verification that
devices sysfs path are actually backed by sysfs. Relaxing this verification
is useful for testing purposes.
`nss-systemd`:
* `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize

17
src/libsystemd/sd-device/sd-device.c
View file

@ -13,6 +13,7 @@
#include "device-private.h"
#include "device-util.h"
#include "dirent-util.h"
#include "env-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "format-util.h"
@ -20,6 +21,7 @@
#include "hashmap.h"
#include "id128-util.h"
#include "macro.h"
#include "missing_magic.h"
#include "netlink-util.h"
#include "parse-util.h"
#include "path-util.h"
@ -208,6 +210,21 @@ int device_set_syspath(sd_device *device, const char *_syspath, bool verify) {
return log_debug_errno(SYNTHETIC_ERRNO(ENODEV),
"sd-device: the syspath \"%s\" is not a directory.", syspath);
}
/* Only operate on sysfs, i.e. refuse going down into /sys/fs/cgroup/ or similar places where
* things are not arranged as kobjects in kernel, and hence don't necessarily have
* kobject/attribute structure. */
r = getenv_bool_secure("SYSTEMD_DEVICE_VERIFY_SYSFS");
if (r < 0 && r != -ENXIO)
log_debug_errno(r, "Failed to parse $SYSTEMD_DEVICE_VERIFY_SYSFS value: %m");
if (r != 0) {
r = fd_is_fs_type(fd, SYSFS_MAGIC);
if (r < 0)
return log_debug_errno(r, "sd-device: failed to check if syspath \"%s\" is backed by sysfs.", syspath);
if (r == 0)
return log_debug_errno(SYNTHETIC_ERRNO(ENODEV),
"sd-device: the syspath \"%s\" is outside of sysfs, refusing.", syspath);
}
} else {
syspath = strdup(_syspath);
if (!syspath)

4
test/udev-test.pl
View file

@ -33,6 +33,10 @@ BEGIN {
}
}
# Relax sd-device's sysfs verification, since we want to provide a fake sysfs
# here that actually is a tmpfs.
$ENV{"SYSTEMD_DEVICE_VERIFY_SYSFS"}="0";
my $udev_bin = "./test-udev";
my $valgrind = 0;
my $gdb = 0;