try_add_tainted_module() allocates the tracking record without zeroing
it and initializes the fields in this order:
mod_taint = kmalloc_obj(*mod_taint);
strscpy(mod_taint->name, mod->name, MODULE_NAME_LEN);
mod_taint->taints = mod->taints;
list_add_rcu(&mod_taint->list, &unloaded_tainted_modules);
mod_taint->count = 1;
The record is published by list_add_rcu() before the count field is
written. The readers, unloaded_tainted_modules_seq_show() (debugfs,
under rcu_read_lock()) and print_unloaded_tainted_modules() (panic
path, under guard(rcu)), traverse the list under RCU and read
mod_taint->count. module_mutex, which the writer holds, does not
exclude RCU readers.
A reader that observes the new node between the list_add_rcu() and
the count store reads an uninitialized u64 left over from previous
slab use. This is a data race and leaks kernel heap residue through
the debugfs file and the panic message.
The race window is two adjacent instructions; it is reachable when a
tainted module is unloaded (rmmod) concurrently with a read of
/sys/kernel/debug/module/unloaded_tainted, or with the module list
printout of an oops on another CPU.
Fix this by initializing count before the record is published.
Found during a static-analysis-assisted audit: candidate sites were
surfaced by a Coccinelle rule, and the reader/writer paths were
confirmed by LLM-assisted (GLM-5.3) code inspection. The issue was
not observed at runtime; it is identified by code inspection only.
Fixes: 99bd9956551b ("module: Introduce module unload taint tracking")
Signed-off-by: Binbin Deng <[email protected]>
---
kernel/module/tracking.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/module/tracking.c b/kernel/module/tracking.c
index 9033ff54c4e2..9e8902600c32 100644
--- a/kernel/module/tracking.c
+++ b/kernel/module/tracking.c
@@ -38,8 +38,8 @@ int try_add_tainted_module(struct module *mod)
return -ENOMEM;
strscpy(mod_taint->name, mod->name, MODULE_NAME_LEN);
mod_taint->taints = mod->taints;
- list_add_rcu(&mod_taint->list, &unloaded_tainted_modules);
mod_taint->count = 1;
+ list_add_rcu(&mod_taint->list, &unloaded_tainted_modules);
out:
return 0;
}
--
2.43.0
