commit f5d4e04634c9cf68bdf23de08ada0bb92e8befe7 upstream. 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@xxxxxxxxx Link: https://lkml.kernel.org/r/20240520132621.4054-2-konishi.ryusuke@xxxxxxxxx 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@xxxxxxxxx> Reported-by: "Bai, Shuangpeng" <sjb7183@xxxxxxx> Closes: https://groups.google.com/g/syzkaller/c/MK_LYqtt8ko/m/8rgdWeseAwAJ Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Please apply this patch to the stable trees indicated by the subject prefix instead of the patch that failed. This patch is tailored to replace a call to timer_shutdown_sync(), which does not yet exist in these versions, with an equivalent function call, and is applicable from v4.15 to v6.1. Also, all the builds and tests I did on each stable tree passed. Thanks, Ryusuke Konishi fs/nilfs2/segment.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c index 006df4eac9fa..dfc459a62fb3 100644 --- a/fs/nilfs2/segment.c +++ b/fs/nilfs2/segment.c @@ -2159,8 +2159,10 @@ static void nilfs_segctor_start_timer(struct nilfs_sc_info *sci) { 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); @@ -2378,10 +2380,21 @@ int nilfs_construct_dsync_segment(struct super_block *sb, struct inode *inode, */ 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); } /** @@ -2407,7 +2420,7 @@ static void nilfs_segctor_notify(struct nilfs_sc_info *sci, int mode, int err) 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); } @@ -2597,6 +2610,7 @@ static int nilfs_segctor_thread(void *arg) int timeout = 0; sci->sc_timer_task = current; + timer_setup(&sci->sc_timer, nilfs_construction_timeout, 0); /* start sync. */ sci->sc_task = current; @@ -2663,6 +2677,7 @@ static int nilfs_segctor_thread(void *arg) end_thread: /* end sync. */ sci->sc_task = NULL; + del_timer_sync(&sci->sc_timer); wake_up(&sci->sc_wait_task); /* for nilfs_segctor_kill_thread() */ spin_unlock(&sci->sc_state_lock); return 0; @@ -2726,7 +2741,6 @@ static struct nilfs_sc_info *nilfs_segctor_new(struct super_block *sb, 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; @@ -2812,7 +2826,6 @@ static void nilfs_segctor_destroy(struct nilfs_sc_info *sci) down_write(&nilfs->ns_segctor_sem); - del_timer_sync(&sci->sc_timer); kfree(sci); } -- 2.43.0
