In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_frag: fix stack OOB read while fragmenting IPv4 packets when 'act_mirred' tries to fragment IPv4 packets that had been previously re-assembled using 'act_ct', splats like the following can be observed on kernels built with KASAN: BUG: KASAN: stack-out-of-bounds in ip_do_fragment+0x1b03/0x1f60 Read of size 1 at addr ffff888147009574 by task ping/947 CPU: 0 PID: 947 Comm: ping Not tainted 5.12.0-rc6+ #418 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014 Call Trace: <IRQ> dump_stack+0x92/0xc1 print_address_description.constprop.7+0x1a/0x150 kasan_report.cold.13+0x7f/0x111 ip_do_fragment+0x1b03/0x1f60 sch_fragment+0x4bf/0xe40 tcf_mirred_act+0xc3d/0x11a0 [act_mirred] tcf_action_exec+0x104/0x3e0 fl_classify+0x49a/0x5e0 [cls_flower] tcf_classify_ingress+0x18a/0x820 __netif_receive_skb_core+0xae7/0x3340 __netif_receive_skb_one_core+0xb6/0x1b0 process_backlog+0x1ef/0x6c0 __napi_poll+0xaa/0x500 net_rx_action+0x702/0xac0 __do_softirq+0x1e4/0x97f do_softirq+0x71/0x90 </IRQ> __local_bh_enable_ip+0xdb/0xf0 ip_finish_output2+0x760/0x2120 ip_do_fragment+0x15a5/0x1f60 __ip_finish_output+0x4c2/0xea0 ip_output+0x1ca/0x4d0 ip_send_skb+0x37/0xa0 raw_sendmsg+0x1c4b/0x2d00 sock_sendmsg+0xdb/0x110 __sys_sendto+0x1d7/0x2b0 __x64_sys_sendto+0xdd/0x1b0 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f82e13853eb Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 f3 0f 1e fa 48 8d 05 75 42 2c 00 41 89 ca 8b 00 85 c0 75 14 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 75 c3 0f 1f 40 00 41 57 4d 89 c7 41 56 41 89 RSP: 002b:00007ffe01fad888 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 00005571aac13700 RCX: 00007f82e13853eb RDX: 0000000000002330 RSI: 00005571aac13700 RDI: 0000000000000003 RBP: 0000000000002330 R08: 00005571aac10500 R09: 0000000000000010 R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe01faefb0 R13: 00007ffe01fad890 R14: 00007ffe01fad980 R15: 00005571aac0f0a0 The buggy address belongs to the page: page:000000001dff2e03 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x147009 flags: 0x17ffffc0001000(reserved) raw: 0017ffffc0001000 ffffea00051c0248 ffffea00051c0248 0000000000000000 raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff888147009400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff888147009480: f1 f1 f1 f1 04 f2 f2 f2 f2 f2 f2 f2 00 00 00 00 >ffff888147009500: 00 00 00 00 00 00 00 00 00 00 f2 f2 f2 f2 f2 f2 ^ ffff888147009580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff888147009600: 00 00 00 00 00 00 00 00 00 00 00 00 00 f2 f2 f2 for IPv4 packets, sch_fragment() uses a temporary struct dst_entry. Then, in the following call graph: ip_do_fragment() ip_skb_dst_mtu() ip_dst_mtu_maybe_forward() ip_mtu_locked() the pointer to struct dst_entry is used as pointer to struct rtable: this turns the access to struct members like rt_mtu_locked into an OOB read in the stack. Fix this changing the temporary variable used for IPv4 packets in sch_fragment(), similarly to what is done for IPv6 few lines below.

In the Linux kernel, the following vulnerability has been resolved: ACPI: GTDT: Don't corrupt interrupt mappings on watchdow probe failure When failing the driver probe because of invalid firmware properties, the GTDT driver unmaps the interrupt that it mapped earlier. However, it never checks whether the mapping of the interrupt actially succeeded. Even more, should the firmware report an illegal interrupt number that overlaps with the GIC SGI range, this can result in an IPI being unmapped, and subsequent fireworks (as reported by Dann Frazier). Rework the driver to have a slightly saner behaviour and actually check whether the interrupt has been mapped before unmapping things.

In the Linux kernel, the following vulnerability has been resolved: NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds Fix shift out-of-bounds in xprt_calc_majortimeo(). This is caused by a garbage timeout (retrans) mount option being passed to nfs mount, in this case from syzkaller. If the protocol is XPRT_TRANSPORT_UDP, then 'retrans' is a shift value for a 64-bit long integer, so 'retrans' cannot be >= 64. If it is >= 64, fail the mount and return an error.

In the Linux kernel, the following vulnerability has been resolved: tpm: efi: Use local variable for calculating final log size When tpm_read_log_efi is called multiple times, which happens when one loads and unloads a TPM2 driver multiple times, then the global variable efi_tpm_final_log_size will at some point become a negative number due to the subtraction of final_events_preboot_size occurring each time. Use a local variable to avoid this integer underflow. The following issue is now resolved: Mar 8 15:35:12 hibinst kernel: Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Mar 8 15:35:12 hibinst kernel: Workqueue: tpm-vtpm vtpm_proxy_work [tpm_vtpm_proxy] Mar 8 15:35:12 hibinst kernel: RIP: 0010:__memcpy+0x12/0x20 Mar 8 15:35:12 hibinst kernel: Code: 00 b8 01 00 00 00 85 d2 74 0a c7 05 44 7b ef 00 0f 00 00 00 c3 cc cc cc 66 66 90 66 90 48 89 f8 48 89 d1 48 c1 e9 03 83 e2 07 <f3> 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1 f3 a4 Mar 8 15:35:12 hibinst kernel: RSP: 0018:ffff9ac4c0fcfde0 EFLAGS: 00010206 Mar 8 15:35:12 hibinst kernel: RAX: ffff88f878cefed5 RBX: ffff88f878ce9000 RCX: 1ffffffffffffe0f Mar 8 15:35:12 hibinst kernel: RDX: 0000000000000003 RSI: ffff9ac4c003bff9 RDI: ffff88f878cf0e4d Mar 8 15:35:12 hibinst kernel: RBP: ffff9ac4c003b000 R08: 0000000000001000 R09: 000000007e9d6073 Mar 8 15:35:12 hibinst kernel: R10: ffff9ac4c003b000 R11: ffff88f879ad3500 R12: 0000000000000ed5 Mar 8 15:35:12 hibinst kernel: R13: ffff88f878ce9760 R14: 0000000000000002 R15: ffff88f77de7f018 Mar 8 15:35:12 hibinst kernel: FS: 0000000000000000(0000) GS:ffff88f87bd00000(0000) knlGS:0000000000000000 Mar 8 15:35:12 hibinst kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Mar 8 15:35:12 hibinst kernel: CR2: ffff9ac4c003c000 CR3: 00000001785a6004 CR4: 0000000000060ee0 Mar 8 15:35:12 hibinst kernel: Call Trace: Mar 8 15:35:12 hibinst kernel: tpm_read_log_efi+0x152/0x1a7 Mar 8 15:35:12 hibinst kernel: tpm_bios_log_setup+0xc8/0x1c0 Mar 8 15:35:12 hibinst kernel: tpm_chip_register+0x8f/0x260 Mar 8 15:35:12 hibinst kernel: vtpm_proxy_work+0x16/0x60 [tpm_vtpm_proxy] Mar 8 15:35:12 hibinst kernel: process_one_work+0x1b4/0x370 Mar 8 15:35:12 hibinst kernel: worker_thread+0x53/0x3e0 Mar 8 15:35:12 hibinst kernel: ? process_one_work+0x370/0x370

In the Linux kernel, the following vulnerability has been resolved: md/raid1: properly indicate failure when ending a failed write request This patch addresses a data corruption bug in raid1 arrays using bitmaps. Without this fix, the bitmap bits for the failed I/O end up being cleared. Since we are in the failure leg of raid1_end_write_request, the request either needs to be retried (R1BIO_WriteError) or failed (R1BIO_Degraded).

In the Linux kernel, the following vulnerability has been resolved: sfc: farch: fix TX queue lookup in TX flush done handling We're starting from a TXQ instance number ('qid'), not a TXQ type, so efx_get_tx_queue() is inappropriate (and could return NULL, leading to panics).

In the Linux kernel, the following vulnerability has been resolved: sfc: farch: fix TX queue lookup in TX event handling We're starting from a TXQ label, not a TXQ type, so efx_channel_get_tx_queue() is inappropriate (and could return NULL, leading to panics).

In the Linux kernel, the following vulnerability has been resolved: ext4: always panic when errors=panic is specified Before commit 014c9caa29d3 ("ext4: make ext4_abort() use __ext4_error()"), the following series of commands would trigger a panic: 1. mount /dev/sda -o ro,errors=panic test 2. mount /dev/sda -o remount,abort test After commit 014c9caa29d3, remounting a file system using the test mount option "abort" will no longer trigger a panic. This commit will restore the behaviour immediately before commit 014c9caa29d3. (However, note that the Linux kernel's behavior has not been consistent; some previous kernel versions, including 5.4 and 4.19 similarly did not panic after using the mount option "abort".) This also makes a change to long-standing behaviour; namely, the following series commands will now cause a panic, when previously it did not: 1. mount /dev/sda -o ro,errors=panic test 2. echo test > /sys/fs/ext4/sda/trigger_fs_error However, this makes ext4's behaviour much more consistent, so this is a good thing.

In the Linux kernel, the following vulnerability has been resolved: media: staging/intel-ipu3: Fix memory leak in imu_fmt We are losing the reference to an allocated memory if try. Change the order of the check to avoid that.

In the Linux kernel, the following vulnerability has been resolved: media: staging/intel-ipu3: Fix set_fmt error handling If there in an error during a set_fmt, do not overwrite the previous sizes with the invalid config. Without this patch, v4l2-compliance ends up allocating 4GiB of RAM and causing the following OOPs [ 38.662975] ipu3-imgu 0000:00:05.0: swiotlb buffer is full (sz: 4096 bytes) [ 38.662980] DMA: Out of SW-IOMMU space for 4096 bytes at device 0000:00:05.0 [ 38.663010] general protection fault: 0000 [#1] PREEMPT SMP

In the Linux kernel, the following vulnerability has been resolved: usb: dwc3: core: Do core softreset when switch mode According to the programming guide, to switch mode for DRD controller, the driver needs to do the following. To switch from device to host: 1. Reset controller with GCTL.CoreSoftReset 2. Set GCTL.PrtCapDir(host mode) 3. Reset the host with USBCMD.HCRESET 4. Then follow up with the initializing host registers sequence To switch from host to device: 1. Reset controller with GCTL.CoreSoftReset 2. Set GCTL.PrtCapDir(device mode) 3. Reset the device with DCTL.CSftRst 4. Then follow up with the initializing registers sequence Currently we're missing step 1) to do GCTL.CoreSoftReset and step 3) of switching from host to device. John Stult reported a lockup issue seen with HiKey960 platform without these steps[1]. Similar issue is observed with Ferry's testing platform[2]. So, apply the required steps along with some fixes to Yu Chen's and John Stultz's version. The main fixes to their versions are the missing wait for clocks synchronization before clearing GCTL.CoreSoftReset and only apply DCTL.CSftRst when switching from host to device. [1] https://lore.kernel.org/linux-usb/20210108015115.27920-1-john.stultz@linaro.org/ [2] https://lore.kernel.org/linux-usb/0ba7a6ba-e6a7-9cd4-0695-64fc927e01f1@gmail.com/

In the Linux kernel, the following vulnerability has been resolved: tools/power turbostat: Fix offset overflow issue in index converting The idx_to_offset() function returns type int (32-bit signed), but MSR_PKG_ENERGY_STAT is u32 and would be interpreted as a negative number. The end result is that it hits the if (offset < 0) check in update_msr_sum() which prevents the timer callback from updating the stat in the background when long durations are used. The similar issue exists in offset_to_idx() and update_msr_sum(). Fix this issue by converting the 'int' to 'off_t' accordingly.

In the Linux kernel, the following vulnerability has been resolved: tracing: Restructure trace_clock_global() to never block It was reported that a fix to the ring buffer recursion detection would cause a hung machine when performing suspend / resume testing. The following backtrace was extracted from debugging that case: Call Trace: trace_clock_global+0x91/0xa0 __rb_reserve_next+0x237/0x460 ring_buffer_lock_reserve+0x12a/0x3f0 trace_buffer_lock_reserve+0x10/0x50 __trace_graph_return+0x1f/0x80 trace_graph_return+0xb7/0xf0 ? trace_clock_global+0x91/0xa0 ftrace_return_to_handler+0x8b/0xf0 ? pv_hash+0xa0/0xa0 return_to_handler+0x15/0x30 ? ftrace_graph_caller+0xa0/0xa0 ? trace_clock_global+0x91/0xa0 ? __rb_reserve_next+0x237/0x460 ? ring_buffer_lock_reserve+0x12a/0x3f0 ? trace_event_buffer_lock_reserve+0x3c/0x120 ? trace_event_buffer_reserve+0x6b/0xc0 ? trace_event_raw_event_device_pm_callback_start+0x125/0x2d0 ? dpm_run_callback+0x3b/0xc0 ? pm_ops_is_empty+0x50/0x50 ? platform_get_irq_byname_optional+0x90/0x90 ? trace_device_pm_callback_start+0x82/0xd0 ? dpm_run_callback+0x49/0xc0 With the following RIP: RIP: 0010:native_queued_spin_lock_slowpath+0x69/0x200 Since the fix to the recursion detection would allow a single recursion to happen while tracing, this lead to the trace_clock_global() taking a spin lock and then trying to take it again: ring_buffer_lock_reserve() { trace_clock_global() { arch_spin_lock() { queued_spin_lock_slowpath() { /* lock taken */ (something else gets traced by function graph tracer) ring_buffer_lock_reserve() { trace_clock_global() { arch_spin_lock() { queued_spin_lock_slowpath() { /* DEAD LOCK! */ Tracing should *never* block, as it can lead to strange lockups like the above. Restructure the trace_clock_global() code to instead of simply taking a lock to update the recorded "prev_time" simply use it, as two events happening on two different CPUs that calls this at the same time, really doesn't matter which one goes first. Use a trylock to grab the lock for updating the prev_time, and if it fails, simply try again the next time. If it failed to be taken, that means something else is already updating it. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212761

In the Linux kernel, the following vulnerability has been resolved: dm rq: fix double free of blk_mq_tag_set in dev remove after table load fails When loading a device-mapper table for a request-based mapped device, and the allocation/initialization of the blk_mq_tag_set for the device fails, a following device remove will cause a double free. E.g. (dmesg): device-mapper: core: Cannot initialize queue for request-based dm-mq mapped device device-mapper: ioctl: unable to set up device queue for new table. Unable to handle kernel pointer dereference in virtual kernel address space Failing address: 0305e098835de000 TEID: 0305e098835de803 Fault in home space mode while using kernel ASCE. AS:000000025efe0007 R3:0000000000000024 Oops: 0038 ilc:3 [#1] SMP Modules linked in: ... lots of modules ... Supported: Yes, External CPU: 0 PID: 7348 Comm: multipathd Kdump: loaded Tainted: G W X 5.3.18-53-default #1 SLE15-SP3 Hardware name: IBM 8561 T01 7I2 (LPAR) Krnl PSW : 0704e00180000000 000000025e368eca (kfree+0x42/0x330) R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3 Krnl GPRS: 000000000000004a 000000025efe5230 c1773200d779968d 0000000000000000 000000025e520270 000000025e8d1b40 0000000000000003 00000007aae10000 000000025e5202a2 0000000000000001 c1773200d779968d 0305e098835de640 00000007a8170000 000003ff80138650 000000025e5202a2 000003e00396faa8 Krnl Code: 000000025e368eb8: c4180041e100 lgrl %r1,25eba50b8 000000025e368ebe: ecba06b93a55 risbg %r11,%r10,6,185,58 #000000025e368ec4: e3b010000008 ag %r11,0(%r1) >000000025e368eca: e310b0080004 lg %r1,8(%r11) 000000025e368ed0: a7110001 tmll %r1,1 000000025e368ed4: a7740129 brc 7,25e369126 000000025e368ed8: e320b0080004 lg %r2,8(%r11) 000000025e368ede: b904001b lgr %r1,%r11 Call Trace: [<000000025e368eca>] kfree+0x42/0x330 [<000000025e5202a2>] blk_mq_free_tag_set+0x72/0xb8 [<000003ff801316a8>] dm_mq_cleanup_mapped_device+0x38/0x50 [dm_mod] [<000003ff80120082>] free_dev+0x52/0xd0 [dm_mod] [<000003ff801233f0>] __dm_destroy+0x150/0x1d0 [dm_mod] [<000003ff8012bb9a>] dev_remove+0x162/0x1c0 [dm_mod] [<000003ff8012a988>] ctl_ioctl+0x198/0x478 [dm_mod] [<000003ff8012ac8a>] dm_ctl_ioctl+0x22/0x38 [dm_mod] [<000000025e3b11ee>] ksys_ioctl+0xbe/0xe0 [<000000025e3b127a>] __s390x_sys_ioctl+0x2a/0x40 [<000000025e8c15ac>] system_call+0xd8/0x2c8 Last Breaking-Event-Address: [<000000025e52029c>] blk_mq_free_tag_set+0x6c/0xb8 Kernel panic - not syncing: Fatal exception: panic_on_oops When allocation/initialization of the blk_mq_tag_set fails in dm_mq_init_request_queue(), it is uninitialized/freed, but the pointer is not reset to NULL; so when dev_remove() later gets into dm_mq_cleanup_mapped_device() it sees the pointer and tries to uninitialize and free it again. Fix this by setting the pointer to NULL in dm_mq_init_request_queue() error-handling. Also set it to NULL in dm_mq_cleanup_mapped_device().

In the Linux kernel, the following vulnerability has been resolved: media: dvbdev: Fix memory leak in dvb_media_device_free() dvb_media_device_free() is leaking memory. Free `dvbdev->adapter->conn` before setting it to NULL, as documented in include/media/media-device.h: "The media_entity instance itself must be freed explicitly by the driver if required."

In the Linux kernel, the following vulnerability has been resolved: thermal/drivers/cpufreq_cooling: Fix slab OOB issue Slab OOB issue is scanned by KASAN in cpu_power_to_freq(). If power is limited below the power of OPP0 in EM table, it will cause slab out-of-bound issue with negative array index. Return the lowest frequency if limited power cannot found a suitable OPP in EM table to fix this issue. Backtrace: [<ffffffd02d2a37f0>] die+0x104/0x5ac [<ffffffd02d2a5630>] bug_handler+0x64/0xd0 [<ffffffd02d288ce4>] brk_handler+0x160/0x258 [<ffffffd02d281e5c>] do_debug_exception+0x248/0x3f0 [<ffffffd02d284488>] el1_dbg+0x14/0xbc [<ffffffd02d75d1d4>] __kasan_report+0x1dc/0x1e0 [<ffffffd02d75c2e0>] kasan_report+0x10/0x20 [<ffffffd02d75def8>] __asan_report_load8_noabort+0x18/0x28 [<ffffffd02e6fce5c>] cpufreq_power2state+0x180/0x43c [<ffffffd02e6ead80>] power_actor_set_power+0x114/0x1d4 [<ffffffd02e6fac24>] allocate_power+0xaec/0xde0 [<ffffffd02e6f9f80>] power_allocator_throttle+0x3ec/0x5a4 [<ffffffd02e6ea888>] handle_thermal_trip+0x160/0x294 [<ffffffd02e6edd08>] thermal_zone_device_check+0xe4/0x154 [<ffffffd02d351cb4>] process_one_work+0x5e4/0xe28 [<ffffffd02d352f44>] worker_thread+0xa4c/0xfac [<ffffffd02d360124>] kthread+0x33c/0x358 [<ffffffd02d289940>] ret_from_fork+0xc/0x18

In the Linux kernel, the following vulnerability has been resolved: net: fix use-after-free in tw_timer_handler A real world panic issue was found as follow in Linux 5.4. BUG: unable to handle page fault for address: ffffde49a863de28 PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0 RIP: 0010:tw_timer_handler+0x20/0x40 Call Trace: <IRQ> call_timer_fn+0x2b/0x120 run_timer_softirq+0x1ef/0x450 __do_softirq+0x10d/0x2b8 irq_exit+0xc7/0xd0 smp_apic_timer_interrupt+0x68/0x120 apic_timer_interrupt+0xf/0x20 This issue was also reported since 2017 in the thread [1], unfortunately, the issue was still can be reproduced after fixing DCCP. The ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net namespace is destroyed since tcp_sk_ops is registered befrore ipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops in the list of pernet_list. There will be a use-after-free on net->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net if there are some inflight time-wait timers. This bug is not introduced by commit f2bf415cfed7 ("mib: add net to NET_ADD_STATS_BH") since the net_statistics is a global variable instead of dynamic allocation and freeing. Actually, commit 61a7e26028b9 ("mib: put net statistics on struct net") introduces the bug since it put net statistics on struct net and free it when net namespace is destroyed. Moving init_ipv4_mibs() to the front of tcp_init() to fix this bug and replace pr_crit() with panic() since continuing is meaningless when init_ipv4_mibs() fails. [1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1

In the Linux kernel, the following vulnerability has been resolved: binder: fix async_free_space accounting for empty parcels In 4.13, commit 74310e06be4d ("android: binder: Move buffer out of area shared with user space") fixed a kernel structure visibility issue. As part of that patch, sizeof(void *) was used as the buffer size for 0-length data payloads so the driver could detect abusive clients sending 0-length asynchronous transactions to a server by enforcing limits on async_free_size. Unfortunately, on the "free" side, the accounting of async_free_space did not add the sizeof(void *) back. The result was that up to 8-bytes of async_free_space were leaked on every async transaction of 8-bytes or less. These small transactions are uncommon, so this accounting issue has gone undetected for several years. The fix is to use "buffer_size" (the allocated buffer size) instead of "size" (the logical buffer size) when updating the async_free_space during the free operation. These are the same except for this corner case of asynchronous transactions with payloads < 8 bytes.

In the Linux kernel, the following vulnerability has been resolved: i2c: validate user data in compat ioctl Wrong user data may cause warning in i2c_transfer(), ex: zero msgs. Userspace should not be able to trigger warnings, so this patch adds validation checks for user data in compact ioctl to prevent reported warnings

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear. ffs_data_clear is indirectly called from both ffs_fs_kill_sb and ffs_ep0_release, so it ends up being called twice when userland closes ep0 and then unmounts f_fs. If userland provided an eventfd along with function's USB descriptors, it ends up calling eventfd_ctx_put as many times, causing a refcount underflow. NULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls. Also, set epfiles to NULL right after de-allocating it, for readability. For completeness, ffs_data_clear actually ends up being called thrice, the last call being before the whole ffs structure gets freed, so when this specific sequence happens there is a second underflow happening (but not being reported): /sys/kernel/debug/tracing# modprobe usb_f_fs /sys/kernel/debug/tracing# echo ffs_data_clear > set_ftrace_filter /sys/kernel/debug/tracing# echo function > current_tracer /sys/kernel/debug/tracing# echo 1 > tracing_on (setup gadget, run and kill function userland process, teardown gadget) /sys/kernel/debug/tracing# echo 0 > tracing_on /sys/kernel/debug/tracing# cat trace smartcard-openp-436 [000] ..... 1946.208786: ffs_data_clear <-ffs_data_closed smartcard-openp-431 [000] ..... 1946.279147: ffs_data_clear <-ffs_data_closed smartcard-openp-431 [000] .n... 1946.905512: ffs_data_clear <-ffs_data_put Warning output corresponding to above trace: [ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c [ 1946.293094] refcount_t: underflow; use-after-free. [ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E) [ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G C OE 5.15.0-1-rpi #1 Debian 5.15.3-1 [ 1946.417950] Hardware name: BCM2835 [ 1946.425442] Backtrace: [ 1946.432048] [<c08d60a0>] (dump_backtrace) from [<c08d62ec>] (show_stack+0x20/0x24) [ 1946.448226] r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c [ 1946.458412] [<c08d62cc>] (show_stack) from [<c08d9ae0>] (dump_stack+0x28/0x30) [ 1946.470380] [<c08d9ab8>] (dump_stack) from [<c0123500>] (__warn+0xe8/0x154) [ 1946.482067] r5:c04a948c r4:c0a71dc8 [ 1946.490184] [<c0123418>] (__warn) from [<c08d6948>] (warn_slowpath_fmt+0xa0/0xe4) [ 1946.506758] r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04 [ 1946.517070] [<c08d68ac>] (warn_slowpath_fmt) from [<c04a948c>] (refcount_warn_saturate+0x110/0x15c) [ 1946.535309] r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0 [ 1946.546708] [<c04a937c>] (refcount_warn_saturate) from [<c0380134>] (eventfd_ctx_put+0x48/0x74) [ 1946.564476] [<c03800ec>] (eventfd_ctx_put) from [<bf5464e8>] (ffs_data_clear+0xd0/0x118 [usb_f_fs]) [ 1946.582664] r5:c3b84c00 r4:c2695b00 [ 1946.590668] [<bf546418>] (ffs_data_clear [usb_f_fs]) from [<bf547cc0>] (ffs_data_closed+0x9c/0x150 [usb_f_fs]) [ 1946.609608] r5:bf54d014 r4:c2695b00 [ 1946.617522] [<bf547c24>] (ffs_data_closed [usb_f_fs]) from [<bf547da0>] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs]) [ 1946.636217] r7:c0dfcb ---truncated---