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gpt-auto-generator: be more defensive when checking the presence of ESP in fstab

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Looking for the ESP node is useful to shortcut things but if we're told that
the node is not referenced in fstab that doesn't necessarily mean that ESP is
not mounted via fstab. Indeed the check is not reliable in all cases. Firstly
because it assumes that udev already set the symlinks up. This is not the case
for initrd-less boots. Secondly the devname of the ESP partition can be wrongly
constructed by the dissect code. For example, the approach which consists in
appending "p<partnum>" suffix to construct the partition devname from the disk
devname doesn't work for DM devices.

Hence this patch makes the logic more defensive and do not mount neither ESP
nor XBOOTLDR automatically if any path in paths that starts with /efi or /boot
exists.
This commit is contained in:
Franck Bui 2024-02-07 13:41:48 +01:00
parent de39202426
commit 8a1326581d
4 changed files with 55 additions and 52 deletions
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16
man/systemd-gpt-auto-generator.xml
View File

@ -32,18 +32,22 @@
<para><filename>systemd-gpt-auto-generator</filename> is a unit generator that automatically discovers
the root partition, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>,
<filename>/var/tmp/</filename>, the EFI System Partition, the Extended Boot Loader Partition, and swap
partitions and creates mount and swap units for them, based on the partition type GUIDs of GUID partition
tables (GPT). See <ulink url="https://uefi.org/specifications">UEFI Specification</ulink>, chapter 5 for
more details. It implements the <ulink
<filename>/var/tmp/</filename>, the EFI System Partition (ESP), the Extended Boot Loader Partition
(XBOOTLDR), and swap partitions and creates mount and swap units for them, based on the partition type
GUIDs of GUID partition tables (GPT). See <ulink url="https://uefi.org/specifications">UEFI
Specification</ulink>, chapter 5 for more details. It implements the <ulink
url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable
Partitions Specification</ulink>.</para>
<para>Note that this generator has no effect on non-GPT systems. It will also not create mount point
configuration for directories which already contain files or if the mount point is explicitly configured
in <citerefentry
project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. If
the units this generator creates are overridden, for example by units in directories with higher
project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Additionally
no unit will be created for the ESP or the XBOOTLDR partition if mount entries are found in the
<filename>/boot/</filename> or <filename>/efi/</filename> hierarchies in <citerefentry
project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>If the units this generator creates are overridden, for example by units in directories with higher
precedence, drop-ins and additional dependencies created by this generator might still be used.</para>
<para>This generator will only look for the root partition on the same physical disk where the EFI System

61
src/gpt-auto-generator/gpt-auto-generator.c
View File

@ -463,18 +463,6 @@ static int add_automount(
return generator_add_symlink(arg_dest, SPECIAL_LOCAL_FS_TARGET, "wants", unit);
}
static int slash_boot_in_fstab(void) {
static int cache = -1;
if (cache >= 0)
return cache;
cache = fstab_is_mount_point("/boot");
if (cache < 0)
return log_error_errno(cache, "Failed to parse fstab: %m");
return cache;
}
static int add_partition_xbootldr(DissectedPartition *p) {
_cleanup_free_ char *options = NULL;
int r;
@ -486,14 +474,6 @@ static int add_partition_xbootldr(DissectedPartition *p) {
return 0;
}
r = slash_boot_in_fstab();
if (r < 0)
return r;
if (r > 0) {
log_debug("/boot/ specified in fstab, ignoring XBOOTLDR partition.");
return 0;
}
r = path_is_busy("/boot");
if (r < 0)
return r;
@ -523,18 +503,6 @@ static int add_partition_xbootldr(DissectedPartition *p) {
}
#if ENABLE_EFI
static int slash_efi_in_fstab(void) {
static int cache = -1;
if (cache >= 0)
return cache;
cache = fstab_is_mount_point("/efi");
if (cache < 0)
return log_error_errno(cache, "Failed to parse fstab: %m");
return cache;
}
static bool slash_boot_exists(void) {
static int cache = -1;
@ -574,27 +542,16 @@ static int add_partition_esp(DissectedPartition *p, bool has_xbootldr) {
* Otherwise, if /efi/ is unused and empty (or missing), we'll take that.
* Otherwise, we do nothing. */
if (!has_xbootldr && slash_boot_exists()) {
r = slash_boot_in_fstab();
r = path_is_busy("/boot");
if (r < 0)
return r;
if (r == 0) {
r = path_is_busy("/boot");
if (r < 0)
return r;
if (r == 0) {
esp_path = "/boot";
id = "boot";
}
esp_path = "/boot";
id = "boot";
}
}
if (!esp_path) {
r = slash_efi_in_fstab();
if (r < 0)
return r;
if (r > 0)
return 0;
r = path_is_busy("/efi");
if (r < 0)
return r;
@ -781,6 +738,18 @@ static int process_loader_partitions(DissectedPartition *esp, DissectedPartition
assert(esp);
assert(xbootldr);
/* If any paths in fstab look similar to our favorite paths for ESP or XBOOTLDR, we just exit
* early. We also don't bother with cases where one is configured explicitly and the other shall be
* mounted automatically. */
r = fstab_has_mount_point_prefix_strv(STRV_MAKE("/boot", "/efi"));
if (r > 0) {
log_debug("Found mount entries in the /boot/ or /efi/ hierarchies in fstab, not generating ESP or XBOOTLDR mounts.");
return 0;
}
if (r < 0)
log_debug_errno(r, "Failed to check fstab existing paths, ignoring: %m");
if (!is_efi_boot()) {
log_debug("Not an EFI boot, skipping loader partition UUID check.");
goto mount;

28
src/shared/fstab-util.c
View File

@ -105,6 +105,34 @@ static int fstab_is_same_node(const char *what_fstab, const char *path) {
return false;
}
int fstab_has_mount_point_prefix_strv(char **prefixes) {
_cleanup_endmntent_ FILE *f = NULL;
assert(prefixes);
/* This function returns true if at least one entry in fstab has a mount point that starts with one
* of the passed prefixes. */
if (!fstab_enabled())
return false;
f = setmntent(fstab_path(), "re");
if (!f)
return errno == ENOENT ? false : -errno;
for (;;) {
struct mntent *me;
errno = 0;
me = getmntent(f);
if (!me)
return errno != 0 ? -errno : false;
if (path_startswith_strv(me->mnt_dir, prefixes))
return true;
}
}
int fstab_is_mount_point_full(const char *where, const char *path) {
_cleanup_endmntent_ FILE *f = NULL;
int r;

2
src/shared/fstab-util.h
View File

@ -25,6 +25,8 @@ static inline int fstab_has_node(const char *path) {
return fstab_is_mount_point_full(NULL, path);
}
int fstab_has_mount_point_prefix_strv(char **prefixes);
int fstab_filter_options(
const char *opts,
const char *names,