tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace fields

Overview

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

tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace fields

In check_synth_field(), when a synthetic event field is a stacktrace (field->is_stack) and the histogram field is not a "long[" stacktrace array, validation falls through to the generic size and signedness comparison.

Because parse_synth_field() sets a stacktrace field's type to "__data_loc unsigned long[]", its size is sizeof(u64) and synth_field_signed() marks it as signed. Consequently, any 8-byte signed scalar histogram field passes the fallback check, and its scalar value is subsequently dereferenced as a kernel stacktrace pointer in get_field_size() and trace_stack().

Furthermore, checking strstr(hist_field->type, "long[") is insufficient because tracepoint fields defined with __bitmask() or __rel_bitmask() also have type "__data_loc unsigned long[]" or "__rel_loc unsigned long[]", whilst create_hist_field() treats them as 4-byte scalar values without HIST_FIELD_FL_STACKTRACE.

Propagate HIST_FIELD_FL_STACKTRACE to variable references and field variables (whilst excluding variable aliases from per-element stacktrace capture), and reject any mismatch between HIST_FIELD_FL_STACKTRACE and field->is_stack in check_synth_field().

Affected

• Linux >= 00cf3d672a9dd409418647e9f98784c339c3ff63 < 1f36e4ddd05d540f363dbaa4c23042549f15b3ef
• Linux >= 00cf3d672a9dd409418647e9f98784c339c3ff63 < deb336ae7c7b341591a6862cf6fcfeca97c77dfd
• Linux >= 00cf3d672a9dd409418647e9f98784c339c3ff63 < a244c241593b5b38a08f0df2cb43c26574efbdcb
• Linux b9453380c1c542fd095a4dbe9251eeba4022bbce
• Linux 5f52389bdd9eafb63b3a2f804e02aeb17b6a5f55
• Linux f3baa42afeea0d5f04ad31525e861199d02210cc
• Linux >= 5.10.237 < 5.11
• Linux >= 5.15.124 < 5.16
• Linux >= 6.1.43 < 6.2
• Linux 6.3

Remediation

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