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ftrace: Do not leak a module's empty page group

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When every mcount_loc entry of a module is skipped,
ftrace_process_locs() leaves the module's first page group linked
with no records. ftrace_release_mod() matches a module's groups by
records[0].ip, which is 0 here, so the group is never freed. While
it stays linked, ftrace_free_mem() reads pg->records[pg->index - 1]
with pg->index == 0 on every later module load, as lookup_rec() did
before commit ee92fa4433 ("ftrace: Fix invalid address access in
lookup_rec() when index is 0").

Unlink and free the new page groups when none of them got a record.

Link: https://patch.msgid.link/20260924-b4-arm64-callops-kcfi-v2-1-587865b6d991@linux.dev
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/all/20260904013350.5141B1F000E9@smtp.kernel.org/
Assisted-by: LLM
Signed-off-by: Jose Fernandez (Anthropic) <jose.fernandez@linux.dev>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Jose Fernandez (Anthropic) 2026-09-24 22:35:45 +00:00 committed by Steven Rostedt
parent 1054e526ce
commit 6703ab347f
1 changed files with 14 additions and 0 deletions
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14
kernel/trace/ftrace.c
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@ -7720,6 +7720,20 @@ static int ftrace_process_locs(struct module *mod,
rec->ip = addr;
}
/*
* ftrace_release_mod() finds a module's page groups by their first
* record. If every entry was skipped there is none, so unlink the
* new page groups and free them now.
*/
if (mod && !start_pg->index) {
ftrace_pages->next = NULL;
mutex_unlock(&ftrace_lock);
/* Need to synchronize with ftrace_location_range() */
synchronize_rcu();
ftrace_free_pages(start_pg);
return 0;
}
if (pg->next) {
pg_unuse = pg->next;
pg->next = NULL;