tracing/histograms: Verify event_call identity when updating synth_event refcount

Overview

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

tracing/histograms: Verify event_call identity when updating synth_event refcount

In event_hist_trigger_parse() and hist_unreg_all(), the histogram registration and unregistration paths look up find_synth_event() using trace_event_name(file->event_call) and adjust se->ref if a match is found.

Because find_synth_event() only compares the event basename, registering or removing a histogram on a non-synthetic trace event whose basename matches a synthetic event erroneously modifies the synthetic event's reference count. If a histogram is registered on the non-synthetic event before the synthetic event is created and removed afterwards, se->ref is decremented without a matching increment, allowing the synthetic event to be freed while an active histogram action still holds a pointer to it.

Introduce find_synth_event_call() to verify that &se->call matches file->event_call before adjusting se->ref.

Affected

• Linux >= 4b147936fa509650beaf638b331573c23ba4d609 < 381f543ed35c434d5b707369aa5dcd69ecf440af
• Linux >= 4b147936fa509650beaf638b331573c23ba4d609 < 4472579bd1c83708b6fe623c870cdf728e947205
• Linux >= 4b147936fa509650beaf638b331573c23ba4d609 < 23b4106e8b35823acc79e206c7745f55b9cfd78b
• Linux >= 4b147936fa509650beaf638b331573c23ba4d609 < 06e816bed499fe47f39f12044382cc5d064485fb
• Linux >= 4b147936fa509650beaf638b331573c23ba4d609 < 5597bb8db6855fcb97a67196d227fea359bcd81c
• Linux >= 4b147936fa509650beaf638b331573c23ba4d609 < cf4e31d5da80fae4c9cdbe7af55b7c3ad213f0e4
• Linux >= 4b147936fa509650beaf638b331573c23ba4d609 < 3403d9bb27ebc3572bd048620746b4414e073bf9
• Linux 4.17

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.