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nilfs2: fix use-after-free of timer for log writer thread

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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: fdce895ea5 ("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>
This commit is contained in:
Ryusuke Konishi 2024-05-20 22:26:19 +09:00 committed by Andrew Morton
parent 1901472fa8
commit f5d4e04634
1 changed files with 19 additions and 6 deletions
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25
fs/nilfs2/segment.c
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@ -2118,8 +2118,10 @@ 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);
@ -2320,10 +2322,21 @@ 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);
}
/**
@ -2349,7 +2362,7 @@ 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);
}
@ -2539,6 +2552,7 @@ 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;
@ -2606,6 +2620,7 @@ static int nilfs_segctor_thread(void *arg)
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_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;
@ -2748,7 +2762,6 @@ static void nilfs_segctor_destroy(struct nilfs_sc_info *sci)
down_write(&nilfs->ns_segctor_sem);
timer_shutdown_sync(&sci->sc_timer);
kfree(sci);
}