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Subject[PATCH -tip] kprobes: Fix an inverted result check for reusing optimized probe
Date
Fix an inverted result check for reusing unused kprobe correctly.
This has been introduced by commit 819319fc9346 ("kprobes: Return
error if we fail to reuse kprobe instead of BUG_ON()"), which
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.

[ 4.563544] Beginning kprobe tests...
[ 4.563648] Probe ARM code
[ 4.563733] kprobe
[ 4.564700] kretprobe
[ 4.565538] ARM instruction simulation
[ 4.565671] Check decoding tables
[ 4.565883] Run test cases
[ 5.070700] FAIL: test_case_handler not run
[ 5.070938] FAIL: Test andge r10, r11, r14, asr r7
[ 5.071118] FAIL: Scenario 11
...
[ 74.174729] FAIL: Scenario 7
[ 74.211776] Total instruction simulation tests=1631, pass=1433 fail=198
[ 74.212168] 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>
Fixes: 819319fc9346 ("kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()")
Cc: stable@vger.kernel.org # v5.0+
---
kernel/kprobes.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index c83e54727131..b1ea30a5540e 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -709,7 +709,6 @@ static void unoptimize_kprobe(struct kprobe *p, bool force)
static int reuse_unused_kprobe(struct kprobe *ap)
{
struct optimized_kprobe *op;
- int ret;

/*
* Unused kprobe MUST be on the way of delayed unoptimizing (means
@@ -720,9 +719,8 @@ 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;
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