Re: [PATCH v3 17/30] liveupdate: luo_files: luo_ioctl: Unregister all FDs on device close
From: Pratyush Yadav <pratyush@kernel.org>
Date: 2025-08-27 15:34:41
Also in:
linux-api, linux-fsdevel, linux-mm, lkml
Hi Pasha, On Thu, Aug 07 2025, Pasha Tatashin wrote:
Currently, a file descriptor registered for preservation via the remains globally registered with LUO until it is explicitly unregistered. This creates a potential for resource leaks into the next kernel if the userspace agent crashes or exits without proper cleanup before a live update is fully initiated. This patch ties the lifetime of FD preservation requests to the lifetime of the open file descriptor for /dev/liveupdate, creating an implicit "session". When the /dev/liveupdate file descriptor is closed (either explicitly via close() or implicitly on process exit/crash), the .release handler, luo_release(), is now called. This handler invokes the new function luo_unregister_all_files(), which iterates through all FDs that were preserved through that session and unregisters them.
Why special case files here? Shouldn't you undo all the serialization done for all the subsystems? Anyway, this is buggy. I found this when testing the memfd patches. If you preserve a memfd and close the /dev/liveupdate FD before reboot, luo_unregister_all_files() calls the cancel callback, which calls kho_unpreserve_folio(). But kho_unpreserve_folio() fails because KHO is still in finalized state. This doesn't happen when cancelling explicitly because luo_cancel() calls kho_abort(). I think you should just make the release go through the cancel flow, since the operation is essentially a cancel anyway. There are subtle differences here though, since the release might be called before prepare, so we need to be careful of that.
quoted hunk ↗ jump to hunk
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com> --- kernel/liveupdate/luo_files.c | 19 +++++++++++++++++++ kernel/liveupdate/luo_internal.h | 1 + kernel/liveupdate/luo_ioctl.c | 1 + 3 files changed, 21 insertions(+)diff --git a/kernel/liveupdate/luo_files.c b/kernel/liveupdate/luo_files.c index 33577c9e9a64..63f8b086b785 100644 --- a/kernel/liveupdate/luo_files.c +++ b/kernel/liveupdate/luo_files.c@@ -721,6 +721,25 @@ int luo_unregister_file(u64 token) return ret; } +/** + * luo_unregister_all_files - Unpreserve all currently registered files. + * + * Iterates through all file descriptors currently registered for preservation + * and unregisters them, freeing all associated resources. This is typically + * called when LUO agent exits. + */ +void luo_unregister_all_files(void) +{ + struct luo_file *luo_file; + unsigned long token; + + luo_state_read_enter(); + xa_for_each(&luo_files_xa_out, token, luo_file) + __luo_unregister_file(token); + luo_state_read_exit(); + WARN_ON_ONCE(atomic64_read(&luo_files_count) != 0); +} + /** * luo_retrieve_file - Find a registered file instance by its token. * @token: The unique token of the file instance to retrieve.diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h index 5692196fd425..189e032d7738 100644 --- a/kernel/liveupdate/luo_internal.h +++ b/kernel/liveupdate/luo_internal.h@@ -37,5 +37,6 @@ void luo_do_subsystems_cancel_calls(void); int luo_retrieve_file(u64 token, struct file **filep); int luo_register_file(u64 token, int fd); int luo_unregister_file(u64 token); +void luo_unregister_all_files(void); #endif /* _LINUX_LUO_INTERNAL_H */diff --git a/kernel/liveupdate/luo_ioctl.c b/kernel/liveupdate/luo_ioctl.c index 6f61569c94e8..7ca33d1c868f 100644 --- a/kernel/liveupdate/luo_ioctl.c +++ b/kernel/liveupdate/luo_ioctl.c@@ -137,6 +137,7 @@ static int luo_open(struct inode *inodep, struct file *filep) static int luo_release(struct inode *inodep, struct file *filep) { + luo_unregister_all_files(); atomic_set(&luo_device_in_use, 0); return 0;
-- Regards, Pratyush Yadav