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livepatch: fix RCU usage in klp_find_external_symbol() 

While one must hold RCU-sched (aka. preempt_disable) for find_symbol()
one must equally hold it over the use of the object returned.

The moment you release the RCU-sched read lock, the object can be dead
and gone.

[jkosina@suse.cz: change subject line to be aligned with other patches]
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.cz>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Peter Zijlstra 2015-02-28 22:24:48 +01:00 committed by Jiri Kosina
parent c4ce0da8ec
commit c064a0de1b
1 changed files with 2 additions and 1 deletions
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3
kernel/livepatch/core.c
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@ -248,11 +248,12 @@ static int klp_find_external_symbol(struct module *pmod, const char *name,
/* first, check if it's an exported symbol */
preempt_disable();
sym = find_symbol(name, NULL, NULL, true, true);
preempt_enable();
if (sym) {
*addr = sym->value;
preempt_enable();
return 0;
}
preempt_enable();
/* otherwise check if it's in another .o within the patch module */
return klp_find_object_symbol(pmod->name, name, addr);