{"id":"AZL-104810","summary":"CVE-2026-97921 affecting package kernel 6.6.157.1-1","details":"In the Linux kernel, the following vulnerability has been resolved:\n\ntracing: Free histogram the field rejected for a bad modifier\n\nWriting a hist trigger whose value or variable carries a modifier that is\nnot allowed there leaks the fields that were built for it.\n\n__create_val_field() takes the field from parse_expr() and stores it in\nhist_data-\u003efields[] only after the modifier checks have run:\n\n\thist_field = parse_expr(hist_data, file, field_str, flags, var_name,\n\t\t\t\t&n_subexprs);\n\t...\n\tif (hist_field-\u003eflags & HIST_FIELD_FL_VAR) {\n\t\tif (hist_field-\u003eflags & (...))\n\t\t\tgoto err;\n\t} else {\n\t\tif (hist_field-\u003eflags & (...))\n\t\t\tgoto err;\n\t}\n\n\thist_data-\u003efields[val_idx] = hist_field;\n\nBoth checks jump past that store, and the err label returns without\nfreeing anything. The error unwinds to create_hist_data(), which calls\ndestroy_hist_data() -\u003e destroy_hist_fields(), and that reaches a field\nonly by walking fields[]. A field that never got there is unreachable.\n\ncommit e0213434fe3e (\"tracing: Do not let histogram values have some\nmodifiers\") set ret to -EINVAL and fell through to the store, which left\nthe field owned by fields[] and freed along with the rest of hist_data.\nSplitting the check into a value case and a variable case replaced that\nfall-through with a goto that skips it.\n\nWith CONFIG_DEBUG_KMEMLEAK, 200 writes of\n\n  # echo 'hist:keys=prev_pid:vals=next_pid.log2' \u003e \\\n\t events/sched/sched_switch/trigger\n\neach correctly rejected with -EINVAL, leave 332 unreferenced objects\n(63744 bytes) reported at create_hist_field(); 200 install and remove\ncycles of a valid trigger leave none. A '.log2' field is two\nallocations, since create_hist_field() puts the plain field in\noperands[0] of the log2 field, and both are reported.\n\nUse destroy_hist_field() rather than __destroy_hist_field() so that\noperands[0] is freed as well. It returns early for HIST_FIELD_FL_VAR_REF,\nwhich is what an operand owned by hist_data-\u003evar_refs[] needs; the\nrejected field itself is never a var ref, because a var ref never carries\na modifier flag.","modified":"2026-09-26T14:16:24.029802844Z","published":"2026-09-25T11:17:19Z","upstream":["CVE-2026-97921"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-97921"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.157.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-104810.json"}}],"schema_version":"1.9.0"}