On Fri, 26 Apr 2024 15:34:08 +0800 Tze-nan wu <tze-nan...@mediatek.com> wrote:
> "tracing_event_file" is at the risk of use-after-free due to the race of > two functions "tracing_open_file_tr" and "synth_event_release". > Specifically, it could be freed by synth_event_release before > tracing_open_file_tr has the opportunity to access its members. > > It's easy to reproduced by first executing script 'A' and then script 'B' > in my environment. > > Script 'A': > echo "hello int aaa" > /sys/kernel/tracing/synthetic_events > while : > do > echo 0 > /sys/kernel/tracing/events/synthetic/hello/enable > done > > Script 'B': > echo > /sys/kernel/tracing/synthetic/events I think you meant: echo > /sys/kernel/tracing/synthetic_events > > My environment: > arm64 + generic and swtag based KASAN both enabled + kernel-6.6.18 > > KASAN report > ================================================================== > BUG: KASAN: slab-use-after-free in tracing_open_file_tr > Read of size 8 at addr 9*ffff********** by task sh/3485 > Pointer tag: [9*], memory tag: [fe] > > CPU: * PID: 3485 Comm: sh Tainted: **************** > Call trace: > __hwasan_tag_mismatch > tracing_open_file_tr > do_dentry_open > vfs_open > path_openat > > Freed by task 3490: > slab_free_freelist_hook > kmem_cache_free > event_file_put > remove_event_file_dir > __trace_remove_event_call > trace_remove_event_call > synth_event_release > dyn_events_release_all > synth_events_open > > page last allocated via order 0, migratetype Unmovable: > __slab_alloc > kmem_cache_alloc > trace_create_new_event > trace_add_event_call > register_synth_event > __create_synth_event > create_or_delete_synth_event > trace_parse_run_command > synth_events_write > vfs_write Thanks for reporting this. > > Based on the assumption that eventfs_inode will persist throughout the > execution of the tracing_open_file_tr function, > we can fix this issue by incrementing the reference count of > trace_event_file once it is assigned to eventfs_inode->data. > The reference count will then be decremented during the release phase of > eventfs_inode. > > This ensures that trace_event_file is not prematurely freed while the > tracing_open_file_tr function is being called. > > Fixes: bb32500fb9b7 ("tracing: Have trace_event_file have ref counters") > Co-developed-by: Cheng-Jui Wang <cheng-jui.w...@mediatek.com> > Signed-off-by: Cheng-Jui Wang <cheng-jui.w...@mediatek.com> > Signed-off-by: Tze-nan wu <tze-nan...@mediatek.com> > --- > BTW, I've also attempted to reproduce the same issue in another > environment (described below). > It's also reproducible but in a lower rate. > > another environment: > x86 + ubuntu + generic kasan enabled + kernel-6.9-rc4 > > After applying the patch, KASAN no longer reports any issues when > following the same reproduction steps in my arm64 environment. > However, I am concerned about potential side effects that the patch might > introduce. > Additionally, the newly added function "is_entry_event_callback" may not > be reliable in my opinion, > as the callback function used in the comparison could change in future. > Nonetheless, this is the best solution I can come up with now. > > Looking for any suggestion or solution, appreciate. Yeah, I do not think eventfs should be involved in this. It needs to be protected at a higher level (in the synthetic/dynamic event code). I'm just coming back from Japan, and I'll need to take a deeper look at this after I recover from my jetlag. Thanks, -- Steve