kprobes: Fix error check when reusing optimized probes

BugLink: https://bugs.launchpad.net/bugs/1838349
commit 5f843ed415581cfad4ef8fefe31c138a8346ca8a upstream.

The following commit introduced a bug in one of our error paths:

  819319fc9346 ("kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()")

it missed to handle the return value of kprobe_optready() as
error-value. In reality, the kprobe_optready() returns a bool
result, so "true" case must be passed instead of 0.

This causes some errors on kprobe boot-time selftests on ARM:

 [   ] Beginning kprobe tests...
 [   ] Probe ARM code
 [   ]     kprobe
 [   ]     kretprobe
 [   ] ARM instruction simulation
 [   ]     Check decoding tables
 [   ]     Run test cases
 [   ] FAIL: test_case_handler not run
 [   ] FAIL: Test andge	r10, r11, r14, asr r7
 [   ] FAIL: Scenario 11
 ...
 [   ] FAIL: Scenario 7
 [   ] Total instruction simulation tests=1631, pass=1433 fail=198
 [   ] kprobe tests failed

This can happen if an optimized probe is unregistered and next
kprobe is registered on same address until the previous probe
is not reclaimed.

If this happens, a hidden aggregated probe may be kept in memory,
and no new kprobe can probe same address. Also, in that case
register_kprobe() will return "1" instead of minus error value,
which can mislead caller logic.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S . Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Naveen N . Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org # v5.0+
Fixes: 819319fc9346 ("kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()")
Link: http://lkml.kernel.org/r/155530808559.32517.539898325433642204.stgit@devnote2
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 0df0b66b17c2194406a18ec4ed135d273b144c1d..4641bcecd161b54138695e5113a49d7a7cefbb33 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -703,7 +703,6 @@ static void unoptimize_kprobe(struct kprobe *p, bool force)
 static int reuse_unused_kprobe(struct kprobe *ap)
 {
        struct optimized_kprobe *op;
-       int ret;
 
        BUG_ON(!kprobe_unused(ap));
        /*
@@ -715,9 +714,8 @@ static int reuse_unused_kprobe(struct kprobe *ap)
        /* Enable the probe again */
        ap->flags &= ~KPROBE_FLAG_DISABLED;
        /* Optimize it again (remove from op->list) */
-       ret = kprobe_optready(ap);
-       if (ret)
-               return ret;
+       if (!kprobe_optready(ap))
+               return -EINVAL;
 
        optimize_kprobe(ap);
        return 0;