The patch titled Subject: nilfs2: fix use-after-free of timer for log writer thread has been added to the -mm mm-hotfixes-unstable branch. Its filename is nilfs2-fix-use-after-free-of-timer-for-log-writer-thread.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ryusuke Konishi konishi.ryusuke@gmail.com Subject: nilfs2: fix use-after-free of timer for log writer thread Date: Mon, 20 May 2024 22:26:19 +0900

Patch series "nilfs2: fix log writer related issues".

This bug fix series covers three nilfs2 log writer-related issues, including a timer use-after-free issue and potential deadlock issue on unmount, and a potential freeze issue in event synchronization found during their analysis. Details are described in each commit log.

This patch (of 3):

A use-after-free issue has been reported regarding the timer sc_timer on the nilfs_sc_info structure.

The problem is that even though it is used to wake up a sleeping log writer thread, sc_timer is not shut down until the nilfs_sc_info structure is about to be freed, and is used regardless of the thread's lifetime.

Fix this issue by limiting the use of sc_timer only while the log writer thread is alive.

Link: https://lkml.kernel.org/r/20240520132621.4054-1-konishi.ryusuke@gmail.com Link: https://lkml.kernel.org/r/20240520132621.4054-2-konishi.ryusuke@gmail.com Fixes: fdce895ea5dd ("nilfs2: change sc_timer from a pointer to an embedded one in struct nilfs_sc_info") Signed-off-by: Ryusuke Konishi konishi.ryusuke@gmail.com Reported-by: "Bai, Shuangpeng" sjb7183@psu.edu Closes: https://groups.google.com/g/syzkaller/c/MK_LYqtt8ko/m/8rgdWeseAwAJ Tested-by: Ryusuke Konishi konishi.ryusuke@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/nilfs2/segment.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-)

--- a/fs/nilfs2/segment.c~nilfs2-fix-use-after-free-of-timer-for-log-writer-thread +++ a/fs/nilfs2/segment.c @@ -2118,8 +2118,10 @@ static void nilfs_segctor_start_timer(st { spin_lock(&sci->sc_state_lock); if (!(sci->sc_state & NILFS_SEGCTOR_COMMIT)) { - sci->sc_timer.expires = jiffies + sci->sc_interval; - add_timer(&sci->sc_timer); + if (sci->sc_task) { + sci->sc_timer.expires = jiffies + sci->sc_interval; + add_timer(&sci->sc_timer); + } sci->sc_state |= NILFS_SEGCTOR_COMMIT; } spin_unlock(&sci->sc_state_lock); @@ -2320,10 +2322,21 @@ int nilfs_construct_dsync_segment(struct */ static void nilfs_segctor_accept(struct nilfs_sc_info *sci) { + bool thread_is_alive; + spin_lock(&sci->sc_state_lock); sci->sc_seq_accepted = sci->sc_seq_request; + thread_is_alive = (bool)sci->sc_task; spin_unlock(&sci->sc_state_lock); - del_timer_sync(&sci->sc_timer); + + /* + * This function does not race with the log writer thread's + * termination. Therefore, deleting sc_timer, which should not be + * done after the log writer thread exits, can be done safely outside + * the area protected by sc_state_lock. + */ + if (thread_is_alive) + del_timer_sync(&sci->sc_timer); }

/** @@ -2349,7 +2362,7 @@ static void nilfs_segctor_notify(struct sci->sc_flush_request &= ~FLUSH_DAT_BIT;

/* re-enable timer if checkpoint creation was not done */ - if ((sci->sc_state & NILFS_SEGCTOR_COMMIT) && + if ((sci->sc_state & NILFS_SEGCTOR_COMMIT) && sci->sc_task && time_before(jiffies, sci->sc_timer.expires)) add_timer(&sci->sc_timer); } @@ -2539,6 +2552,7 @@ static int nilfs_segctor_thread(void *ar int timeout = 0;

sci->sc_timer_task = current; + timer_setup(&sci->sc_timer, nilfs_construction_timeout, 0);

/* start sync. */ sci->sc_task = current; @@ -2606,6 +2620,7 @@ static int nilfs_segctor_thread(void *ar end_thread: /* end sync. */ sci->sc_task = NULL; + timer_shutdown_sync(&sci->sc_timer); wake_up(&sci->sc_wait_task); /* for nilfs_segctor_kill_thread() */ spin_unlock(&sci->sc_state_lock); return 0; @@ -2669,7 +2684,6 @@ static struct nilfs_sc_info *nilfs_segct INIT_LIST_HEAD(&sci->sc_gc_inodes); INIT_LIST_HEAD(&sci->sc_iput_queue); INIT_WORK(&sci->sc_iput_work, nilfs_iput_work_func); - timer_setup(&sci->sc_timer, nilfs_construction_timeout, 0);

sci->sc_interval = HZ * NILFS_SC_DEFAULT_TIMEOUT; sci->sc_mjcp_freq = HZ * NILFS_SC_DEFAULT_SR_FREQ; @@ -2748,7 +2762,6 @@ static void nilfs_segctor_destroy(struct

down_write(&nilfs->ns_segctor_sem);

- timer_shutdown_sync(&sci->sc_timer); kfree(sci); }

_

Patches currently in -mm which might be from konishi.ryusuke@gmail.com are

nilfs2-fix-use-after-free-of-timer-for-log-writer-thread.patch nilfs2-fix-unexpected-freezing-of-nilfs_segctor_sync.patch nilfs2-fix-potential-hang-in-nilfs_detach_log_writer.patch