==================================================================
BUG: KASAN: slab-use-after-free in gsm_cleanup_mux+0x210/0x2b8 drivers/tty/n_gsm.c:3084
Read at addr f6ff0000057f780c by task syz-executor254/3077
Pointer tag: [f6], memory tag: [fe]

CPU: 0 PID: 3077 Comm: syz-executor254 Not tainted 6.4.0-rc7-syzkaller-00041-ge660abd551f1 #0
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0x94/0xec arch/arm64/kernel/stacktrace.c:233
 show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:240
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x48/0x60 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:351 [inline]
 print_report+0xd8/0x5f4 mm/kasan/report.c:462
 kasan_report+0x7c/0x9c mm/kasan/report.c:572
 __do_kernel_fault+0x174/0x1c0 arch/arm64/mm/fault.c:320
 do_bad_area arch/arm64/mm/fault.c:479 [inline]
 do_tag_check_fault+0x78/0x8c arch/arm64/mm/fault.c:790
 do_mem_abort+0x44/0x94 arch/arm64/mm/fault.c:866
 el1_abort+0x40/0x60 arch/arm64/kernel/entry-common.c:367
 el1h_64_sync_handler+0xd8/0xe4 arch/arm64/kernel/entry-common.c:427
 el1h_64_sync+0x64/0x68 arch/arm64/kernel/entry.S:586
 gsm_cleanup_mux+0x210/0x2b8 drivers/tty/n_gsm.c:3084
 gsm_config drivers/tty/n_gsm.c:3327 [inline]
 gsmld_ioctl+0x5b4/0x86c drivers/tty/n_gsm.c:3733
 tty_ioctl+0x120/0xb50 drivers/tty/tty_io.c:2786
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0xa8/0xec fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x48/0x114 arch/arm64/kernel/syscall.c:52
 el0_svc_common.constprop.0+0x44/0xec arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x38/0xa4 arch/arm64/kernel/syscall.c:193
 el0_svc+0x2c/0xb0 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0xb8/0xbc arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x19c/0x1a0 arch/arm64/kernel/entry.S:591

Allocated by task 3071:
 kasan_save_stack+0x2c/0x54 mm/kasan/common.c:45
 save_stack_info+0x38/0x118 mm/kasan/tags.c:104
 kasan_save_alloc_info+0x14/0x20 mm/kasan/tags.c:138
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 ____kasan_kmalloc mm/kasan/common.c:333 [inline]
 __kasan_kmalloc+0x9c/0xa8 mm/kasan/common.c:383
 kasan_kmalloc include/linux/kasan.h:196 [inline]
 kmalloc_trace+0x4c/0x60 mm/slab_common.c:1062
 kmalloc include/linux/slab.h:559 [inline]
 kzalloc include/linux/slab.h:680 [inline]
 gsm_dlci_alloc+0x30/0x17c drivers/tty/n_gsm.c:2618
 gsm_activate_mux drivers/tty/n_gsm.c:3100 [inline]
 gsm_config drivers/tty/n_gsm.c:3355 [inline]
 gsmld_ioctl+0x62c/0x86c drivers/tty/n_gsm.c:3733
 tty_ioctl+0x120/0xb50 drivers/tty/tty_io.c:2786
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0xa8/0xec fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x48/0x114 arch/arm64/kernel/syscall.c:52
 el0_svc_common.constprop.0+0x44/0xec arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x38/0xa4 arch/arm64/kernel/syscall.c:193
 el0_svc+0x2c/0xb0 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0xb8/0xbc arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x19c/0x1a0 arch/arm64/kernel/entry.S:591

Freed by task 3071:
 kasan_save_stack+0x2c/0x54 mm/kasan/common.c:45
 save_stack_info+0x38/0x118 mm/kasan/tags.c:104
 kasan_save_free_info+0x18/0x24 mm/kasan/tags.c:143
 ____kasan_slab_free.constprop.0+0x190/0x1f8 mm/kasan/common.c:236
 __kasan_slab_free+0x10/0x1c mm/kasan/common.c:244
 kasan_slab_free include/linux/kasan.h:162 [inline]
 slab_free_hook mm/slub.c:1781 [inline]
 slab_free_freelist_hook+0xb4/0x1e8 mm/slub.c:1807
 slab_free mm/slub.c:3786 [inline]
 __kmem_cache_free+0x16c/0x2c0 mm/slub.c:3799
 kfree+0x5c/0x74 mm/slab_common.c:1015
 gsm_dlci_free+0x64/0x78 drivers/tty/n_gsm.c:2671
 tty_port_destructor drivers/tty/tty_port.c:296 [inline]
 kref_put include/linux/kref.h:65 [inline]
 tty_port_put+0xac/0xd4 drivers/tty/tty_port.c:311
 dlci_put drivers/tty/n_gsm.c:2681 [inline]
 gsm_dlci_release drivers/tty/n_gsm.c:2714 [inline]
 gsm_cleanup_mux+0xd8/0x2b8 drivers/tty/n_gsm.c:3074
 gsm_config drivers/tty/n_gsm.c:3327 [inline]
 gsmld_ioctl+0x5b4/0x86c drivers/tty/n_gsm.c:3733
 tty_ioctl+0x120/0xb50 drivers/tty/tty_io.c:2786
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0xa8/0xec fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x48/0x114 arch/arm64/kernel/syscall.c:52
 el0_svc_common.constprop.0+0x44/0xec arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x38/0xa4 arch/arm64/kernel/syscall.c:193
 el0_svc+0x2c/0xb0 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0xb8/0xbc arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x19c/0x1a0 arch/arm64/kernel/entry.S:591

The buggy address belongs to the object at ffff0000057f7800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 12 bytes inside of
 1024-byte region [ffff0000057f7800, ffff0000057f7c00)

The buggy address belongs to the physical page:
page:0000000079801325 refcount:1 mapcount:0 mapping:0000000000000000 index:0xf6ff0000057f7800 pfn:0x457f4
head:0000000079801325 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x1ffc00000010200(slab|head|node=0|zone=0|lastcpupid=0x7ff|kasantag=0x0)
page_type: 0xffffffff()
raw: 01ffc00000010200 f5ff000002c01500 fffffc00000b3510 f1ff000002c00290
raw: f6ff0000057f7800 0000000000100006 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000057f7600: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffff0000057f7700: f8 f8 f8 f8 f8 f8 f8 f8 fe fe fe fe fe fe fe fe
>ffff0000057f7800: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
                   ^
 ffff0000057f7900: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
 ffff0000057f7a00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
==================================================================