[syzbot] [usb?] KASAN: slab-use-after-free Read in ep_open

[syzbot] [usb?] KASAN: slab-use-after-free Read in ep_open

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    365f9c7a6b81 Merge branches 'for-next/core' and 'for-next/..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=13731632580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=72c97575381cec47
dashboard link: https://syzkaller.appspot.com/bug?extid=df9e891bf8ea586f846b
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=136d6499580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=138d6449580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/eafe0adb7386/disk-365f9c7a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/29422d607579/vmlinux-365f9c7a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/98ca955a8b54/Image-365f9c7a.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+df9e891bf8ea586f846b@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_lock_common kernel/locking/mutex.c:625 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock+0x130/0xf14 kernel/locking/mutex.c:821
Read of size 8 at addr ffff0000efe3d058 by task syz-executor/5909

CPU: 1 UID: 0 PID: 5909 Comm: syz-executor Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_address_description+0xb0/0x238 mm/kasan/report.c:378
 print_report+0x68/0x84 mm/kasan/report.c:482
 kasan_report+0x8c/0xc4 mm/kasan/report.c:595
 __asan_report_load8_noabort+0x20/0x2c mm/kasan/report_generic.c:381
 __mutex_lock_common kernel/locking/mutex.c:625 [inline]
 __mutex_lock+0x130/0xf14 kernel/locking/mutex.c:821
 mutex_lock_interruptible_nested+0x24/0x30 kernel/locking/mutex.c:899
 ep_open+0x58/0x25c drivers/usb/gadget/legacy/inode.c:823
 do_dentry_open+0x5c4/0xfc0 fs/open.c:947
 vfs_open+0x44/0x2dc fs/open.c:1052
 do_open fs/namei.c:4700 [inline]
 path_openat+0x21fc/0x2a60 fs/namei.c:4863
 do_file_open+0x1c8/0x2e8 fs/namei.c:4892
 do_sys_openat2+0x114/0x1e8 fs/open.c:1368
 do_sys_open+0xb0/0xe0 fs/open.c:1374
 __do_sys_openat fs/open.c:1390 [inline]
 __se_sys_openat fs/open.c:1385 [inline]
 __arm64_sys_openat+0xa0/0xbc fs/open.c:1385
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

Allocated by task 6282:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:78
 kasan_save_alloc_info+0x44/0x54 mm/kasan/generic.c:570
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x2e8/0x5ec mm/slub.c:5515
 _kmalloc_noprof include/linux/slab.h:969 [inline]
 _kzalloc_noprof include/linux/slab.h:1290 [inline]
 activate_ep_files drivers/usb/gadget/legacy/inode.c:1601 [inline]
 gadgetfs_bind+0x204/0x75c drivers/usb/gadget/legacy/inode.c:1692
 gadget_bind_driver+0x274/0x834 drivers/usb/gadget/udc/core.c:1662
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x29c/0x800 drivers/base/dd.c:706
 __driver_probe_device+0x1e0/0x350 drivers/base/dd.c:868
 driver_probe_device+0x6c/0x19c drivers/base/dd.c:898
 __driver_attach+0x168/0x384 drivers/base/dd.c:1292
 bus_for_each_dev+0x128/0x1b4 drivers/base/bus.c:383
 driver_attach+0x50/0x60 drivers/base/dd.c:1310
 bus_add_driver+0x208/0x500 drivers/base/bus.c:763
 driver_register+0x220/0x310 drivers/base/driver.c:174
 usb_gadget_register_driver_owner+0xf0/0x25c drivers/usb/gadget/udc/core.c:1752
 dev_config+0x91c/0xcc0 drivers/usb/gadget/legacy/inode.c:1883
 vfs_write+0x2a4/0xa0c fs/read_write.c:685
 ksys_write+0x12c/0x228 fs/read_write.c:739
 __do_sys_write fs/read_write.c:750 [inline]
 __se_sys_write fs/read_write.c:747 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:747
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

Freed by task 6283:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:78
 kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x74/0xa4 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2705 [inline]
 slab_free mm/slub.c:6405 [inline]
 kfree+0x188/0x690 mm/slub.c:6720
 put_ep+0xd0/0x144 drivers/usb/gadget/legacy/inode.c:225
 destroy_ep_files+0x244/0x2dc drivers/usb/gadget/legacy/inode.c:1582
 gadgetfs_unbind+0x114/0x1f0 drivers/usb/gadget/legacy/inode.c:1655
 gadget_unbind_driver+0x188/0x790 drivers/usb/gadget/udc/core.c:1724
 device_remove+0xc4/0x134 drivers/base/dd.c:616
 __device_release_driver drivers/base/dd.c:1349 [inline]
 device_release_driver_internal+0x124/0x20c drivers/base/dd.c:1372
 driver_detach+0x124/0x1b4 drivers/base/dd.c:1435
 bus_remove_driver+0x124/0x22c drivers/base/bus.c:832
 driver_unregister+0x78/0xac drivers/base/driver.c:202
 usb_gadget_unregister_driver+0x50/0x78 drivers/usb/gadget/udc/core.c:1784
 dev_release+0x8c/0x15c drivers/usb/gadget/legacy/inode.c:1198
 __fput+0x338/0x74c fs/file_table.c:512
 ____fput+0x20/0x30 fs/file_table.c:540
 task_work_run+0x1cc/0x25c kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x58c/0x1a74 kernel/exit.c:1009
 __do_sys_exit kernel/exit.c:1119 [inline]
 __se_sys_exit kernel/exit.c:1117 [inline]
 do_group_exit+0x0/0x238 kernel/exit.c:1117
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

The buggy address belongs to the object at ffff0000efe3d000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 88 bytes inside of
 freed 512-byte region [ffff0000efe3d000, ffff0000efe3d200)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff0000efe3dc00 pfn:0x12fe3c


---
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Re: [syzbot] [usb?] KASAN: slab-use-after-free Read in ep_open

[syzbot]

syzbot has bisected this issue to:

commit aa00f67adc2c0d6439f81b5a81ff181377c47a7e
Author: Jens Axboe <axboe@kernel.dk>
Date:   Tue Oct 22 19:47:00 2024 +0000

    io_uring: add support for fixed wait regions

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10e60679580000
start commit:   9a143525f62b Merge tag 'ata-7.2-rc7' of git://git.kernel.o..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=12e60679580000
console output: https://syzkaller.appspot.com/x/log.txt?x=14e60679580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c44651ea7dd2f307
dashboard link: https://syzkaller.appspot.com/bug?extid=df9e891bf8ea586f846b
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120defb9580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16323fb9580000

Reported-by: syzbot+df9e891bf8ea586f846b@syzkaller.appspotmail.com
Fixes: aa00f67adc2c ("io_uring: add support for fixed wait regions")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] [usb?] KASAN: slab-use-after-free Read in ep_open

[Jens Axboe]

On 8/17/26 7:42 AM, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit aa00f67adc2c0d6439f81b5a81ff181377c47a7e
> Author: Jens Axboe <axboe@kernel.dk>
> Date:   Tue Oct 22 19:47:00 2024 +0000
> 
>     io_uring: add support for fixed wait regions
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10e60679580000
> start commit:   9a143525f62b Merge tag 'ata-7.2-rc7' of git://git.kernel.o..
> git tree:       upstream
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=12e60679580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=14e60679580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c44651ea7dd2f307
> dashboard link: https://syzkaller.appspot.com/bug?extid=df9e891bf8ea586f846b
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120defb9580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16323fb9580000
> 
> Reported-by: syzbot+df9e891bf8ea586f846b@syzkaller.appspotmail.com
> Fixes: aa00f67adc2c ("io_uring: add support for fixed wait regions")

That looks like nonsense, I strongly suspect it's a race and hence your
bisection ends up being mostly useless as it sends you in random directions.

-- 
Jens Axboe

Re: [syzbot] [usb?] KASAN: slab-use-after-free Read in ep_open

[Alan Stern]

On Mon, Aug 17, 2026 at 09:04:06AM -0600, Jens Axboe wrote:
> On 8/17/26 7:42 AM, syzbot wrote:
> > syzbot has bisected this issue to:
> > 
> > commit aa00f67adc2c0d6439f81b5a81ff181377c47a7e
> > Author: Jens Axboe <axboe@kernel.dk>
> > Date:   Tue Oct 22 19:47:00 2024 +0000
> > 
> >     io_uring: add support for fixed wait regions
> > 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10e60679580000
> > start commit:   9a143525f62b Merge tag 'ata-7.2-rc7' of git://git.kernel.o..
> > git tree:       upstream
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=12e60679580000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14e60679580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=c44651ea7dd2f307
> > dashboard link: https://syzkaller.appspot.com/bug?extid=df9e891bf8ea586f846b
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120defb9580000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16323fb9580000
> > 
> > Reported-by: syzbot+df9e891bf8ea586f846b@syzkaller.appspotmail.com
> > Fixes: aa00f67adc2c ("io_uring: add support for fixed wait regions")
> 
> That looks like nonsense, I strongly suspect it's a race and hence your
> bisection ends up being mostly useless as it sends you in random directions.

Agreed.

The patch below has already been sent to the USB mailing list.  Has 
syzbot tested it?

Alan Stern

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/ v7.2

From: Aleksandr Nogikh <nogikh@google.com>

A race condition exists between opening a gadgetfs endpoint file and the
destruction of the endpoint files, leading to a use-after-free of the
ep_data object.

When an endpoint file is opened, the VFS looks up the dentry and calls
ep_open(). ep_open() retrieves the ep_data pointer from inode->i_private
and attempts to lock its mutex. Concurrently, if the gadget is unbound,
destroy_ep_files() iterates over the endpoints, unhashes their dentries,
and immediately calls put_ep(). This drops the initial reference to the
ep_data object, freeing it. If another thread is already in the process of
opening the file, it holds a reference to the dentry and the inode. The
inode remains alive, and its i_private pointer still points to the
now-freed ep_data. When ep_open() proceeds to lock data->lock, it accesses
freed memory.

BUG: KASAN: slab-use-after-free in __mutex_lock_common
kernel/locking/mutex.c:625 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock+0x130/0xf14
kernel/locking/mutex.c:821
Read of size 8 at addr ffff0000f43acc58 by task syz-executor/5900

Call trace:
 __mutex_lock_common kernel/locking/mutex.c:625 [inline]
 __mutex_lock+0x130/0xf14 kernel/locking/mutex.c:821
 mutex_lock_interruptible_nested+0x24/0x30 kernel/locking/mutex.c:899
 ep_open+0x58/0x25c drivers/usb/gadget/legacy/inode.c:823
 do_dentry_open+0x5c4/0xfc0 fs/open.c:947
 vfs_open+0x44/0x2dc fs/open.c:1052

Freed by task 6138:
 kfree+0x188/0x690 mm/slub.c:6692
 put_ep+0xd0/0x144 drivers/usb/gadget/legacy/inode.c:225
 destroy_ep_files+0x244/0x2dc drivers/usb/gadget/legacy/inode.c:1582
 gadgetfs_unbind+0x114/0x1f0 drivers/usb/gadget/legacy/inode.c:1655
 gadget_unbind_driver+0x188/0x790 drivers/usb/gadget/udc/core.c:1724

To fix this, tie the base reference of ep_data to the lifetime of the inode
rather than manually dropping it in destroy_ep_files(). Add an .evict_inode
callback to gadget_fs_operations that drops the reference when the inode is
finally destroyed. Remove the premature put_ep() call from
destroy_ep_files(). Additionally, to prevent a double-free in the error
path of activate_ep_files(), clear inode->i_private in
gadgetfs_create_file() before calling iput() if simple_start_creating()
fails.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot
Reported-by: syzbot+df9e891bf8ea586f846b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=df9e891bf8ea586f846b
Link: https://syzkaller.appspot.com/ai_job?id=ae49a838-5eb9-4227-93a3-56ad2313483a
Signed-off-by: Aleksandr Nogikh <nogikh@google.com>

---
diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index d87a8ab51..a03062986 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -1579,8 +1579,6 @@ static void destroy_ep_files (struct dev_data *dev)
 		/* break link to dcache */
 		simple_remove_by_name(dev->sb->s_root, ep->name, NULL);
 
-		put_ep (ep);
-
 		spin_lock_irq (&dev->lock);
 	}
 	spin_unlock_irq (&dev->lock);
@@ -1996,6 +1994,7 @@ static int gadgetfs_create_file (struct super_block *sb, char const *name,
 
 	dentry = simple_start_creating(sb->s_root, name);
 	if (IS_ERR(dentry)) {
+		inode->i_private = NULL;
 		iput(inode);
 		return PTR_ERR(dentry);
 	}
@@ -2006,9 +2005,18 @@ static int gadgetfs_create_file (struct super_block *sb, char const *name,
 	return 0;
 }
 
+static void gadgetfs_evict_inode(struct inode *inode)
+{
+	truncate_inode_pages_final(&inode->i_data);
+	clear_inode(inode);
+	if (inode->i_private && inode->i_fop == &ep_io_operations)
+		put_ep(inode->i_private);
+}
+
 static const struct super_operations gadget_fs_operations = {
 	.statfs =	simple_statfs,
 	.drop_inode =	inode_just_drop,
+	.evict_inode =	gadgetfs_evict_inode,
 };
 
 static int


base-commit: f5098b6bae761e346ebcd9da7f95622c04733cff
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