In the Linux kernel, the following vulnerability has been resolved: erofs: Fix detection of atomic context Current check for atomic context is not sufficient as z_erofs_decompressqueue_endio can be called under rcu lock from blk_mq_flu…

Overview

In the Linux kernel, the following vulnerability has been resolved:

erofs: Fix detection of atomic context

Current check for atomic context is not sufficient as z_erofs_decompressqueue_endio can be called under rcu lock from blk_mq_flush_plug_list(). See the stacktrace [1]

In such case we should hand off the decompression work for async processing rather than trying to do sync decompression in current context. Patch fixes the detection by checking for rcu_read_lock_any_held() and while at it use more appropriate !in_task() check than in_atomic().

Background: Historically erofs would always schedule a kworker for decompression which would incur the scheduling cost regardless of the context. But z_erofs_decompressqueue_endio() may not always be in atomic context and we could actually benefit from doing the decompression in z_erofs_decompressqueue_endio() if we are in thread context, for example when running with dm-verity. This optimization was later added in patch [2] which has shown improvement in performance benchmarks.

============================================== [1] Problem stacktrace [name:core&]BUG: sleeping function called from invalid context at kernel/locking/mutex.c:291 [name:core&]in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1615, name: CpuMonitorServi [name:core&]preempt_count: 0, expected: 0 [name:core&]RCU nest depth: 1, expected: 0 CPU: 7 PID: 1615 Comm: CpuMonitorServi Tainted: G S W OE 6.1.25-android14-5-maybe-dirty-mainline #1 Hardware name: MT6897 (DT) Call trace: dump_backtrace+0x108/0x15c show_stack+0x20/0x30 dump_stack_lvl+0x6c/0x8c dump_stack+0x20/0x48 __might_resched+0x1fc/0x308 __might_sleep+0x50/0x88 mutex_lock+0x2c/0x110 z_erofs_decompress_queue+0x11c/0xc10 z_erofs_decompress_kickoff+0x110/0x1a4 z_erofs_decompressqueue_endio+0x154/0x180 bio_endio+0x1b0/0x1d8 __dm_io_complete+0x22c/0x280 clone_endio+0xe4/0x280 bio_endio+0x1b0/0x1d8 blk_update_request+0x138/0x3a4 blk_mq_plug_issue_direct+0xd4/0x19c blk_mq_flush_plug_list+0x2b0/0x354 __blk_flush_plug+0x110/0x160 blk_finish_plug+0x30/0x4c read_pages+0x2fc/0x370 page_cache_ra_unbounded+0xa4/0x23c page_cache_ra_order+0x290/0x320 do_sync_mmap_readahead+0x108/0x2c0 filemap_fault+0x19c/0x52c __do_fault+0xc4/0x114 handle_mm_fault+0x5b4/0x1168 do_page_fault+0x338/0x4b4 do_translation_fault+0x40/0x60 do_mem_abort+0x60/0xc8 el0_da+0x4c/0xe0 el0t_64_sync_handler+0xd4/0xfc el0t_64_sync+0x1a0/0x1a4

[2] Link: https://lore.kernel.org/all/[email protected]/

Affected

• linux_kernel >= 4.19, < 6.4.7

Remediation

Upgrade past the affected range:

• linux_kernel 6.4.7