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udev/node: fix issue in removing device node symlink (#38419)

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Fixes #37823.
This commit is contained in:
Luca Boccassi
2025-07-31 23:20:05 +01:00
committed by GitHub
parent 8cc1748ddc fdb8600575
commit cb88cf9760
2 changed files with 215 additions and 95 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/udev/udev-node.c
+102 -52
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@@ -213,6 +213,24 @@ static int stack_directory_find_prioritized_devnode(sd_device *dev, int dirfd, b
return !!*ret;
}
static int link_search_and_update(sd_device *dev, const char *slink, int dirfd, bool add) {
int r;
assert(dev);
assert(slink);
assert(dirfd >= 0);
_cleanup_free_ char *devnode = NULL;
r = stack_directory_find_prioritized_devnode(dev, dirfd, add, &devnode);
if (r < 0)
return log_device_debug_errno(dev, r, "Failed to determine device node with the highest priority for '%s': %m", slink);
if (r > 0)
return node_create_symlink(dev, devnode, slink);
log_device_debug(dev, "No reference left for '%s', removing", slink);
return node_remove_symlink(dev, slink);
}
static int stack_directory_update(sd_device *dev, int fd, bool add) {
const char *id;
int r;
@@ -420,7 +438,7 @@ static int link_update(sd_device *dev, const char *slink, bool add) {
_cleanup_(release_lock_file) LockFile lockfile = LOCK_FILE_INIT; /* #3 */
_cleanup_(rmdir_and_freep) char *dirpath = NULL; /* #2 */
_cleanup_close_ int dirfd = -EBADF; /* #1 */
_cleanup_free_ char *current_id = NULL, *devnode = NULL;
_cleanup_free_ char *current_id = NULL;
int r, current_prio;
assert(dev);
@@ -430,72 +448,104 @@ static int link_update(sd_device *dev, const char *slink, bool add) {
if (r < 0)
return r;
r = node_get_current(slink, dirfd, &current_id, add ? &current_prio : NULL);
if (r < 0 && !ERRNO_IS_DEVICE_ABSENT_OR_EMPTY(r))
return log_device_debug_errno(dev, r, "Failed to get the current device node priority for '%s': %m", slink);
if (add) {
r = node_get_current(slink, dirfd, &current_id, &current_prio);
if (r < 0 && !ERRNO_IS_DEVICE_ABSENT_OR_EMPTY(r))
return log_device_debug_errno(dev, r, "Failed to get the current device node priority for '%s': %m", slink);
}
r = stack_directory_update(dev, dirfd, add);
if (r < 0)
return log_device_debug_errno(dev, r, "Failed to update stack directory for '%s': %m", slink);
if (current_id) {
const char *id;
if (!add) {
_cleanup_free_ char *target = NULL;
r = sd_device_get_device_id(dev, &id);
if (r < 0)
return log_device_debug_errno(dev, r, "Failed to get device id: %m");
/* Especially on 'remove' event, the device ID obtained by node_get_current() may not be
* reliable, as the device node and/or device number may be reused. Hence, let's read the
* devlink here and if it points to our device node, then we need to update the devlink. If
* it points to another device node, then it is already owned by another device, hence we
* should not touch it and keep it as is. */
if (add) {
int prio;
r = readlink_malloc(slink, &target);
if (r < 0) {
if (r != -ENOENT)
log_device_debug_errno(dev, r, "Failed to read symbolic link '%s', ignoring: %m", slink);
r = device_get_devlink_priority(dev, &prio);
if (r < 0)
return log_device_debug_errno(dev, r, "Failed to get devlink priority: %m");
if (streq(current_id, id)) {
if (current_prio <= prio)
/* The devlink is ours and already exists, and the new priority is
* equal or higher than the previous. Hence, it is not necessary to
* recreate it. */
return 0;
/* The devlink priority is downgraded. Another device may have a higher
* priority now. Let's find the device node with the highest priority. */
} else {
if (current_prio > prio)
/* The devlink with a higher priority already exists and is owned by
* another device. Hence, it is not necessary to recreate it. */
return 0;
/* This device has the equal or a higher priority than the current. Let's
* create the devlink to our device node. */
return node_create_symlink(dev, /* devnode = */ NULL, slink);
}
} else {
if (!streq(current_id, id))
/* The devlink already exists and is owned by another device. Hence, it is
* not necessary to recreate it. */
return 0;
/* The current devlink is ours, and the target device will be removed. Hence, we need
* to search the device that has the highest priority. and update the devlink. */
/* The devlink does not exist. Let's find the most suitable owner, and create the
* devlink. This is typically not necessary and does nothing, but for safety in the
* case that the devlink is removed manually. */
return link_search_and_update(dev, slink, dirfd, add);
}
} else {
const char *node;
r = sd_device_get_devname(dev, &node);
if (r < 0)
return log_device_debug_errno(dev, r, "Failed to get device node: %m");
if (streq(node, target)) /* owned by us, needs to update. */
return link_search_and_update(dev, slink, dirfd, add);
/* The devlink does not point to our device node. For extra safety, let's validate the
* current devlink, in case that the devlink is manually modified by user. */
if (!path_startswith(target, "/dev/")) {
log_device_debug(dev, "Symbolic link '%s' points to '%s' which is outside of '/dev/', updating it.", slink, target);
return link_search_and_update(dev, slink, dirfd, add);
}
struct stat st;
if (lstat(target, &st) < 0) {
if (errno != ENOENT)
log_device_debug_errno(dev, errno, "Failed to stat '%s', ignoring: %m", target);
/* The current target device is also already removed? Let's update. */
return link_search_and_update(dev, slink, dirfd, add);
}
if (!IN_SET(st.st_mode & S_IFMT, S_IFBLK, S_IFCHR)) {
log_device_debug(dev, "Symbolic link '%s' points to '%s' which is not a device node, updating it.", slink, target);
return link_search_and_update(dev, slink, dirfd, add);
}
return 0; /* the devlink is owned by another device, and we should keep it as is. */
}
if (!current_id)
/* The requested devlink does not exist, or the target device does not exist and the devlink
* points to a non-existing device. Let's search the device that has the highest priority,
* and update the devlink. */
;
return link_search_and_update(dev, slink, dirfd, add);
const char *id;
r = sd_device_get_device_id(dev, &id);
if (r < 0)
return log_device_debug_errno(dev, r, "Failed to get device id: %m");
int prio;
r = device_get_devlink_priority(dev, &prio);
if (r < 0)
return log_device_debug_errno(dev, r, "Failed to get devlink priority: %m");
if (streq(current_id, id)) {
if (current_prio <= prio)
/* The devlink is ours and already exists, and the new priority is equal or higher
* than the previous. Hence, it is not necessary to recreate it. */
return 0;
/* The devlink priority is downgraded. Another device may have a higher priority now. Let's
* find the device node with the highest priority. */
return link_search_and_update(dev, slink, dirfd, add);
}
r = stack_directory_find_prioritized_devnode(dev, dirfd, add, &devnode);
if (r < 0)
return log_device_debug_errno(dev, r, "Failed to determine device node with the highest priority for '%s': %m", slink);
if (r > 0)
return node_create_symlink(dev, devnode, slink);
if (current_prio > prio)
/* The devlink with a higher priority already exists and is owned by another device. Hence,
* it is not necessary to recreate it. */
return 0;
log_device_debug(dev, "No reference left for '%s', removing", slink);
return node_remove_symlink(dev, slink);
/* This device has the equal or a higher priority than the current. Let's create the devlink to our
* device node. */
return node_create_symlink(dev, /* devnode = */ NULL, slink);
}
static int device_get_devpath_by_devnum(sd_device *dev, char **ret) {