[syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    2c9b3512402e Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=158ef15e980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f4925140c45a2a50
dashboard link: https://syzkaller.appspot.com/bug?extid=1a8e2b31f2ac9bd3d148
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=136eee95980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1510b445980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3c29a41eae6b/disk-2c9b3512.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/938da4f6bc30/vmlinux-2c9b3512.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4f9521f6c1ef/bzImage-2c9b3512.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/1d96e2146be6/mount_0.gz
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/f1a30c7339a7/mount_14.gz
mounted in repro #3: https://storage.googleapis.com/syzbot-assets/b4ae6212a921/mount_18.gz

The issue was bisected to:

commit 3bdb7f161697e2d5123b89fe1778ef17a44858e7
Author: Jaegeuk Kim <jaegeuk@kernel.org>
Date:   Wed Apr 3 23:07:53 2024 +0000

    f2fs: don't set RO when shutting down f2fs

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15dcb445980000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=17dcb445980000
console output: https://syzkaller.appspot.com/x/log.txt?x=13dcb445980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com
Fixes: 3bdb7f161697 ("f2fs: don't set RO when shutting down f2fs")

F2FS-fs (loop4): Mounted with checkpoint version = 48b305e5
F2FS-fs (loop4): Stopped filesystem due to reason: 0
==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: null-ptr-deref in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
BUG: KASAN: null-ptr-deref in __refcount_add include/linux/refcount.h:184 [inline]
BUG: KASAN: null-ptr-deref in __refcount_inc include/linux/refcount.h:241 [inline]
BUG: KASAN: null-ptr-deref in refcount_inc include/linux/refcount.h:258 [inline]
BUG: KASAN: null-ptr-deref in get_task_struct include/linux/sched/task.h:118 [inline]
BUG: KASAN: null-ptr-deref in kthread_stop+0xca/0x630 kernel/kthread.c:704
Write of size 4 at addr 0000000000000028 by task syz-executor169/7772

CPU: 1 PID: 7772 Comm: syz-executor169 Not tainted 6.10.0-syzkaller-11185-g2c9b3512402e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 print_report+0xe8/0x550 mm/kasan/report.c:491
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
 __refcount_add include/linux/refcount.h:184 [inline]
 __refcount_inc include/linux/refcount.h:241 [inline]
 refcount_inc include/linux/refcount.h:258 [inline]
 get_task_struct include/linux/sched/task.h:118 [inline]
 kthread_stop+0xca/0x630 kernel/kthread.c:704
 f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210
 f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
 f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
 __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fac5a221249
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 71 1d 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fac5a1ce218 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fac5a2a8708 RCX: 00007fac5a221249
RDX: 0000000020000140 RSI: 000000008004587d RDI: 0000000000000005
RBP: 00007fac5a2a8700 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fac5a274b1c
R13: 00007fac5a274040 R14: 00007fac5a26e057 R15: 8c02ea27aa268e19
 </TASK>
==================================================================


---
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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

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Re: [syzbot] Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread
Author: lizhi.xu@windriver.com

shutting down f2fs set ro, and check bdev_thaw return value

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index c1ad9b278c47..0e607cb3bc9a 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2244,7 +2244,9 @@ int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsigned int flag,
 		if (ret)
 			goto out;
 		f2fs_stop_checkpoint(sbi, false, STOP_CP_REASON_SHUTDOWN);
-		bdev_thaw(sb->s_bdev);
+		ret = bdev_thaw(sb->s_bdev);
+		if (ret == -EINVAL)
+			goto out;
 		break;
 	case F2FS_GOING_DOWN_METASYNC:
 		/* do checkpoint only */
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index df4cf31f93df..e507379762ff 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4177,7 +4177,7 @@ void f2fs_handle_critical_error(struct f2fs_sb_info *sbi, unsigned char reason,
 	 * RO by shutdown, since RO bypasses thaw_super which can hang the
 	 * system.
 	 */
-	if (continue_fs || f2fs_readonly(sb) || shutdown) {
+	if (continue_fs || f2fs_readonly(sb)) {
 		f2fs_warn(sbi, "Stopped filesystem due to reason: %d", reason);
 		return;
 	}

Re: [syzbot] Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

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linux-kernel@vger.kernel.org.

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Subject: Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread
Author: lizhi.xu@windriver.com

before thread stop and free gc_thread, set sbi->gc_thread to NULL

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..ef7b4b0ed164 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -207,10 +207,10 @@ void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 
 	if (!gc_th)
 		return;
+	sbi->gc_thread = NULL;
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);
-	sbi->gc_thread = NULL;
 }
 
 static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)

Re: [syzbot] Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

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Subject: Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread
Author: lizhi.xu@windriver.com

before thread stop and free gc_thread, set sbi->gc_thread to NULL

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..363f95237383 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -204,13 +204,16 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
 	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	static DEFINE_MUTEX(gct_mutex);
 
 	if (!gc_th)
 		return;
+	mutex_lock(&gct_mutex);
+	sbi->gc_thread = NULL;
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);
-	sbi->gc_thread = NULL;
+	mutex_unlock(&gct_mutex);
 }
 
 static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)

Re: [syzbot] Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread
Author: lizhi.xu@windriver.com

before thread stop and free gc_thread, set sbi->gc_thread to NULL, 
and add lock for reentry f2fs_stop_gc_thread.

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..9d7b10831d88 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -204,13 +204,16 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
 	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	static DEFINE_MUTEX(gct_mutex);
 
 	if (!gc_th)
 		return;
+	mutex_lock(&gct_mutex);
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
-	kfree(gc_th);
 	sbi->gc_thread = NULL;
+	kfree(gc_th);
+	mutex_unlock(&gct_mutex);
 }
 
 static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)

Re: [syzbot] Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread
Author: lizhi.xu@windriver.com

before thread stop and free gc_thread, set sbi->gc_thread to NULL, 
and add lock for reentry f2fs_stop_gc_thread.

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..228cad05b32b 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -203,14 +203,20 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	struct f2fs_gc_kthread *gc_th;
+	static DEFINE_MUTEX(gct_mutex);
 
+	mutex_lock(&gct_mutex);
+	gc_th = sbi->gc_thread;
 	if (!gc_th)
-		return;
+		goto unlock;
+
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
-	kfree(gc_th);
 	sbi->gc_thread = NULL;
+	kfree(gc_th);
+unlock:
+	mutex_unlock(&gct_mutex);
 }
 
 static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)

Re: [syzbot] Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread
Author: lizhi.xu@windriver.com

before thread stop and free gc_thread, set sbi->gc_thread to NULL, 
and add lock for reentry f2fs_stop_gc_thread.

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..462f8957ea9a 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -203,14 +203,20 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	struct f2fs_gc_kthread *gc_th;
+	static DEFINE_MUTEX(gct_mutex);
 
+	mutex_lock(&gct_mutex);
+	gc_th = sbi->gc_thread;
 	if (!gc_th)
-		return;
+		goto unlock;
+
+	sbi->gc_thread = NULL;
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);
-	sbi->gc_thread = NULL;
+unlock:
+	mutex_unlock(&gct_mutex);
 }
 
 static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)

Re: [syzbot] Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread
Author: lizhi.xu@windriver.com

before thread stop and free gc_thread, set sbi->gc_thread to NULL, 
and add lock for reentry f2fs_stop_gc_thread.

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..ebaf6b6fc65c 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -203,14 +203,22 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	struct f2fs_gc_kthread *gc_th;
+	static DEFINE_MUTEX(gct_mutex);
 
-	if (!gc_th)
-		return;
+	mutex_lock(&gct_mutex);
+	gc_th = sbi->gc_thread;
+	printk("gc thread: %p, gc thread valid: %d, %s\n", gc_th, virt_addr_valid(gc_th), __func__);
+	if (!gc_th || !virt_addr_valid(gc_th))
+		goto unlock;
+
+	sbi->gc_thread = NULL;
+	printk("2gc thread: %p, %s\n", gc_th, __func__);
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);
-	sbi->gc_thread = NULL;
+unlock:
+	mutex_unlock(&gct_mutex);
 }
 
 static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)

Re: [syzbot] Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread
Author: lizhi.xu@windriver.com

before thread stop and free gc_thread, set sbi->gc_thread to NULL, 
and add lock for reentry f2fs_stop_gc_thread.

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..484eb5082604 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -203,14 +203,20 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	struct f2fs_gc_kthread *gc_th;
+	static DEFINE_MUTEX(gct_mutex);
 
-	if (!gc_th)
-		return;
+	mutex_lock(&gct_mutex);
+	gc_th = sbi->gc_thread;
+	if (!gc_th || !virt_addr_valid(gc_th))
+		goto unlock;
+
+	sbi->gc_thread = NULL;
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);
-	sbi->gc_thread = NULL;
+unlock:
+	mutex_unlock(&gct_mutex);
 }
 
 static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)

Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[Edward Adam Davis]

add mutex sync remount and shutdown

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..269e11fa477a 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -27,6 +27,7 @@ static struct kmem_cache *victim_entry_slab;
 
 static unsigned int count_bits(const unsigned long *addr,
 				unsigned int offset, unsigned int len);
+static DEFINE_MUTEX(gc_lock);
 
 static int gc_thread_func(void *data)
 {
@@ -203,10 +204,13 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	struct f2fs_gc_kthread *gc_th;
 
-	if (!gc_th)
+	guard(mutex)(&gc_lock);
+	gc_th = sbi->gc_thread;
+	if (!gc_th)
 		return;
+
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);

Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

F2FS-fs (loop3): Stopped filesystem due to reason: 0
==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: null-ptr-deref in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
BUG: KASAN: null-ptr-deref in __refcount_add include/linux/refcount.h:184 [inline]
BUG: KASAN: null-ptr-deref in __refcount_inc include/linux/refcount.h:241 [inline]
BUG: KASAN: null-ptr-deref in refcount_inc include/linux/refcount.h:258 [inline]
BUG: KASAN: null-ptr-deref in get_task_struct include/linux/sched/task.h:118 [inline]
BUG: KASAN: null-ptr-deref in kthread_stop+0xca/0x630 kernel/kthread.c:704
Write of size 4 at addr 0000000000000028 by task syz.3.116/7392

CPU: 0 PID: 7392 Comm: syz.3.116 Not tainted 6.10.0-syzkaller-11185-g2c9b3512402e-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 print_report+0xe8/0x550 mm/kasan/report.c:491
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
 __refcount_add include/linux/refcount.h:184 [inline]
 __refcount_inc include/linux/refcount.h:241 [inline]
 refcount_inc include/linux/refcount.h:258 [inline]
 get_task_struct include/linux/sched/task.h:118 [inline]
 kthread_stop+0xca/0x630 kernel/kthread.c:704
 f2fs_stop_gc_thread+0x73/0xc0 fs/f2fs/gc.c:214
 f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
 f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
 __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f28ae575b59
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f28af3cc048 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f28ae706038 RCX: 00007f28ae575b59
RDX: 0000000020000140 RSI: 000000008004587d RDI: 0000000000000005
RBP: 00007f28ae5e4e5d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f28ae706038 R15: 00007ffeb6d24ae8
 </TASK>
==================================================================


Tested on:

commit:         2c9b3512 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=137bde11980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f4925140c45a2a50
dashboard link: https://syzkaller.appspot.com/bug?extid=1a8e2b31f2ac9bd3d148
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=146ff0d9980000

Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[Edward Adam Davis]

add mutex sync remount and shutdown

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..1f4542a899c3 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -27,6 +27,7 @@ static struct kmem_cache *victim_entry_slab;
 
 static unsigned int count_bits(const unsigned long *addr,
 				unsigned int offset, unsigned int len);
+static DEFINE_MUTEX(gc_lock);
 
 static int gc_thread_func(void *data)
 {
@@ -203,10 +204,13 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	struct f2fs_gc_kthread *gc_th;
 
-	if (!gc_th)
+	guard(mutex)(&gc_lock);
+	gc_th = sbi->gc_thread;
+	if (gc_th < PAGE_OFFSET)
 		return;
+
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);

Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

F2FS-fs (loop1): Stopped filesystem due to reason: 0
==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: null-ptr-deref in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
BUG: KASAN: null-ptr-deref in __refcount_add include/linux/refcount.h:184 [inline]
BUG: KASAN: null-ptr-deref in __refcount_inc include/linux/refcount.h:241 [inline]
BUG: KASAN: null-ptr-deref in refcount_inc include/linux/refcount.h:258 [inline]
BUG: KASAN: null-ptr-deref in get_task_struct include/linux/sched/task.h:118 [inline]
BUG: KASAN: null-ptr-deref in kthread_stop+0xca/0x630 kernel/kthread.c:704
Write of size 4 at addr 0000000000000028 by task syz.1.265/8090

CPU: 1 PID: 8090 Comm: syz.1.265 Not tainted 6.10.0-syzkaller-11185-g2c9b3512402e-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 print_report+0xe8/0x550 mm/kasan/report.c:491
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
 __refcount_add include/linux/refcount.h:184 [inline]
 __refcount_inc include/linux/refcount.h:241 [inline]
 refcount_inc include/linux/refcount.h:258 [inline]
 get_task_struct include/linux/sched/task.h:118 [inline]
 kthread_stop+0xca/0x630 kernel/kthread.c:704
 f2fs_stop_gc_thread+0x83/0xd0 fs/f2fs/gc.c:214
 f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
 f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
 __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f604c575b59
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f604d3e9048 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f604c706038 RCX: 00007f604c575b59
RDX: 0000000020000140 RSI: 000000008004587d RDI: 0000000000000005
RBP: 00007f604c5e4e5d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f604c706038 R15: 00007fff3d7c10f8
 </TASK>
==================================================================


Tested on:

commit:         2c9b3512 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=17f2dd73980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f4925140c45a2a50
dashboard link: https://syzkaller.appspot.com/bug?extid=1a8e2b31f2ac9bd3d148
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=113ee499980000

Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[Edward Adam Davis]

add mutex sync remount and shutdown

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..a624e8271fbc 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -27,6 +27,7 @@ static struct kmem_cache *victim_entry_slab;
 
 static unsigned int count_bits(const unsigned long *addr,
 				unsigned int offset, unsigned int len);
+static DEFINE_MUTEX(gc_lock);
 
 static int gc_thread_func(void *data)
 {
@@ -203,10 +204,13 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	struct f2fs_gc_kthread *gc_th;
 
-	if (!gc_th)
+	guard(mutex)(&gc_lock);
+	gc_th = sbi->gc_thread;
+	if (!gc_th || gc_th->f2fs_gc_task < PAGE_OFFSET)
 		return;
+
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);

Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com
Tested-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com

Tested on:

commit:         2c9b3512 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=13bc41a1980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f4925140c45a2a50
dashboard link: https://syzkaller.appspot.com/bug?extid=1a8e2b31f2ac9bd3d148
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=125559a1980000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[Edward Adam Davis]

use s_umount read lock sync remount and shutdown

#syz test: upstream 2c9b3512402e

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index c1ad9b278c47..3940c0b11868 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2280,7 +2280,9 @@ int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsigned int flag,
 	if (readonly)
 		goto out;
 
+	down_read(&sb->s_umount);
 	f2fs_stop_gc_thread(sbi);
+	up_read(&sb->s_umount);
 	f2fs_stop_discard_thread(sbi);
 
 	f2fs_drop_discard_cmd(sbi);

Re: [syzbot] [f2fs?] KASAN: null-ptr-deref Write in f2fs_stop_gc_thread

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in f2fs_stop_gc_thread

INFO: task syz.1.294:8828 blocked for more than 143 seconds.
      Not tainted 6.10.0-syzkaller-11185-g2c9b3512402e-dirty #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.294       state:D stack:23808 pid:8828  tgid:8827  ppid:5828   flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5188 [inline]
 __schedule+0x17ae/0x4a10 kernel/sched/core.c:6529
 __schedule_loop kernel/sched/core.c:6606 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6621
 schedule_timeout+0xb0/0x310 kernel/time/timer.c:2557
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common kernel/sched/completion.c:116 [inline]
 wait_for_common kernel/sched/completion.c:127 [inline]
 wait_for_completion+0x355/0x620 kernel/sched/completion.c:148
 kthread_stop+0x19e/0x630 kernel/kthread.c:710
 f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210
 f2fs_do_shutdown+0x258/0x550 fs/f2fs/file.c:2284
 f2fs_ioc_shutdown fs/f2fs/file.c:2327 [inline]
 __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4327
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6582b75b59
RSP: 002b:00007f65825ff048 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f6582d05f60 RCX: 00007f6582b75b59
RDX: 0000000020000140 RSI: 000000008004587d RDI: 0000000000000005
RBP: 00007f6582be4e5d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f6582d05f60 R15: 00007fff126c76c8
 </TASK>
INFO: task syz.1.294:8849 blocked for more than 144 seconds.
      Not tainted 6.10.0-syzkaller-11185-g2c9b3512402e-dirty #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.294       state:D stack:26464 pid:8849  tgid:8827  ppid:5828   flags:0x00000004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5188 [inline]
 __schedule+0x17ae/0x4a10 kernel/sched/core.c:6529
 __schedule_loop kernel/sched/core.c:6606 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6621
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
 rwsem_down_write_slowpath+0xeeb/0x13b0 kernel/locking/rwsem.c:1178
 __down_write_common kernel/locking/rwsem.c:1306 [inline]
 __down_write kernel/locking/rwsem.c:1315 [inline]
 down_write+0x1d7/0x220 kernel/locking/rwsem.c:1580
 vfs_cmd_reconfigure fs/fsopen.c:262 [inline]
 vfs_fsconfig_locked fs/fsopen.c:292 [inline]
 __do_sys_fsconfig fs/fsopen.c:473 [inline]
 __se_sys_fsconfig+0xb64/0xf80 fs/fsopen.c:345
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6582b75b59
RSP: 002b:00007f65825de048 EFLAGS: 00000246 ORIG_RAX: 00000000000001af
RAX: ffffffffffffffda RBX: 00007f6582d06038 RCX: 00007f6582b75b59
RDX: 0000000000000000 RSI: 0000000000000007 RDI: 0000000000000006
RBP: 00007f6582be4e5d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f6582d06038 R15: 00007fff126c76c8
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/30:
 #0: ffffffff8e336e60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:327 [inline]
 #0: ffffffff8e336e60 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:839 [inline]
 #0: ffffffff8e336e60 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x2a0 kernel/locking/lockdep.c:6620
3 locks held by kworker/u8:5/144:
2 locks held by getty/4844:
 #0: ffff88802afe40a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc900031332f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x6b5/0x1e10 drivers/tty/n_tty.c:2211
2 locks held by syz.1.294/8828:
 #0: ffff88801fb32420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write_file+0x61/0x200 fs/namespace.c:559
 #1: ffff88801fb320e0 (&type->s_umount_key#53){++++}-{3:3}, at: f2fs_do_shutdown+0x250/0x550 fs/f2fs/file.c:2283
2 locks held by syz.1.294/8849:
 #0: ffff88807eccac70 (&fc->uapi_mutex){+.+.}-{3:3}, at: __do_sys_fsconfig fs/fsopen.c:471 [inline]
 #0: ffff88807eccac70 (&fc->uapi_mutex){+.+.}-{3:3}, at: __se_sys_fsconfig+0x9a7/0xf80 fs/fsopen.c:345
 #1: ffff88801fb320e0 (&type->s_umount_key#53){++++}-{3:3}, at: vfs_cmd_reconfigure fs/fsopen.c:262 [inline]
 #1: ffff88801fb320e0 (&type->s_umount_key#53){++++}-{3:3}, at: vfs_fsconfig_locked fs/fsopen.c:292 [inline]
 #1: ffff88801fb320e0 (&type->s_umount_key#53){++++}-{3:3}, at: __do_sys_fsconfig fs/fsopen.c:473 [inline]
 #1: ffff88801fb320e0 (&type->s_umount_key#53){++++}-{3:3}, at: __se_sys_fsconfig+0xb64/0xf80 fs/fsopen.c:345
2 locks held by syz.4.517/10408:
 #0: ffff88802a168420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write_file+0x61/0x200 fs/namespace.c:559
 #1: ffff88802a1680e0 (&type->s_umount_key#53){++++}-{3:3}, at: f2fs_do_shutdown+0x250/0x550 fs/f2fs/file.c:2283
2 locks held by syz.4.517/10432:
 #0: ffff88801e248470 (&fc->uapi_mutex){+.+.}-{3:3}, at: __do_sys_fsconfig fs/fsopen.c:471 [inline]
 #0: ffff88801e248470 (&fc->uapi_mutex){+.+.}-{3:3}, at: __se_sys_fsconfig+0x9a7/0xf80 fs/fsopen.c:345
 #1: ffff88802a1680e0 (&type->s_umount_key#53){++++}-{3:3}, at: vfs_cmd_reconfigure fs/fsopen.c:262 [inline]
 #1: ffff88802a1680e0 (&type->s_umount_key#53){++++}-{3:3}, at: vfs_fsconfig_locked fs/fsopen.c:292 [inline]
 #1: ffff88802a1680e0 (&type->s_umount_key#53){++++}-{3:3}, at: __do_sys_fsconfig fs/fsopen.c:473 [inline]
 #1: ffff88802a1680e0 (&type->s_umount_key#53){++++}-{3:3}, at: __se_sys_fsconfig+0xb64/0xf80 fs/fsopen.c:345
2 locks held by syz.2.560/10729:
 #0: ffff88807866e420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write_file+0x61/0x200 fs/namespace.c:559
 #1: ffff88807866e0e0 (&type->s_umount_key#53){++++}-{3:3}, at: f2fs_do_shutdown+0x250/0x550 fs/f2fs/file.c:2283
2 locks held by syz.2.560/10730:
 #0: ffff88801cfb5870 (&fc->uapi_mutex){+.+.}-{3:3}, at: __do_sys_fsconfig fs/fsopen.c:471 [inline]
 #0: ffff88801cfb5870 (&fc->uapi_mutex){+.+.}-{3:3}, at: __se_sys_fsconfig+0x9a7/0xf80 fs/fsopen.c:345
 #1: ffff88807866e0e0 (&type->s_umount_key#53){++++}-{3:3}, at: vfs_cmd_reconfigure fs/fsopen.c:262 [inline]
 #1: ffff88807866e0e0 (&type->s_umount_key#53){++++}-{3:3}, at: vfs_fsconfig_locked fs/fsopen.c:292 [inline]
 #1: ffff88807866e0e0 (&type->s_umount_key#53){++++}-{3:3}, at: __do_sys_fsconfig fs/fsopen.c:473 [inline]
 #1: ffff88807866e0e0 (&type->s_umount_key#53){++++}-{3:3}, at: __se_sys_fsconfig+0xb64/0xf80 fs/fsopen.c:345
2 locks held by syz.3.637/11108:
2 locks held by syz.0.640/11110:
2 locks held by syz.2.643/11116:

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 30 Comm: khungtaskd Not tainted 6.10.0-syzkaller-11185-g2c9b3512402e-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 nmi_cpu_backtrace+0x49c/0x4d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x198/0x320 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:223 [inline]
 watchdog+0xfde/0x1020 kernel/hung_task.c:379
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 12 Comm: kworker/u8:1 Not tainted 6.10.0-syzkaller-11185-g2c9b3512402e-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Workqueue: events_unbound cfg80211_wiphy_work
RIP: 0010:get_current arch/x86/include/asm/current.h:49 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x8/0x70 kernel/kcov.c:206
Code: 8b 3d 4c 70 4a 0c 48 89 de 5b e9 73 7c 57 00 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 8b 04 24 <65> 48 8b 0c 25 40 d5 03 00 65 8b 15 70 92 70 7e f7 c2 00 01 ff 00
RSP: 0018:ffffc90000117790 EFLAGS: 00000297
RAX: ffffffff8b03874a RBX: 0000000000000008 RCX: ffff8880172bda00
RDX: 0000000000000000 RSI: 0000000000000008 RDI: 0000000000000002
RBP: 0000000000000014 R08: ffffffff8b03873b R09: 1ffffffff1f5d135
R10: dffffc0000000000 R11: fffffbfff1f5d136 R12: dffffc0000000000
R13: 0000000000000008 R14: ffff88807e0c30d0 R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1c7a489000 CR3: 000000001f196000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <NMI>
 </NMI>
 <TASK>
 ieee80211_sta_get_rates+0x20a/0x660 net/mac80211/util.c:1540
 ieee80211_update_sta_info net/mac80211/ibss.c:989 [inline]
 ieee80211_rx_bss_info net/mac80211/ibss.c:1098 [inline]
 ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1579 [inline]
 ieee80211_ibss_rx_queued_mgmt+0x11e1/0x2d70 net/mac80211/ibss.c:1606
 ieee80211_iface_process_skb net/mac80211/iface.c:1588 [inline]
 ieee80211_iface_work+0x8a5/0xf20 net/mac80211/iface.c:1642
 cfg80211_wiphy_work+0x2db/0x490 net/wireless/core.c:440
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
 worker_thread+0x86d/0xd40 kernel/workqueue.c:3390
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>


Tested on:

commit:         2c9b3512 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14b2bea1980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f4925140c45a2a50
dashboard link: https://syzkaller.appspot.com/bug?extid=1a8e2b31f2ac9bd3d148
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=146ecebd980000

[PATCH] f2fs: Add mutex to prevent gc task from being accessed before initialization

[Edward Adam Davis]

syzbot report null-ptr-deref Write in f2fs_stop_gc_thread, because 
shutdown and remount can cause multi-path entry into f2fs_stop_gc_thread,
resulting in incorrect access to f2fs_gc_task before it is properly
initialized.

Reported-and-tested-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1a8e2b31f2ac9bd3d148
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/f2fs/gc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..a624e8271fbc 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -27,6 +27,7 @@ static struct kmem_cache *victim_entry_slab;
 
 static unsigned int count_bits(const unsigned long *addr,
 				unsigned int offset, unsigned int len);
+static DEFINE_MUTEX(gc_lock);
 
 static int gc_thread_func(void *data)
 {
@@ -203,10 +204,13 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	struct f2fs_gc_kthread *gc_th;
 
-	if (!gc_th)
+	guard(mutex)(&gc_lock);
+	gc_th = sbi->gc_thread;
+	if (!gc_th || gc_th->f2fs_gc_task < PAGE_OFFSET)
 		return;
+
 	kthread_stop(gc_th->f2fs_gc_task);
 	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);
-- 
2.43.0