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SubjectRe: [PATCH] trace: Avoid memory leak in predicate_parse()
On Tue, 28 May 2019 17:43:38 +0200
Tomas Bortoli <tomasbortoli@gmail.com> wrote:

> @@ -578,6 +578,8 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
> out_free:
> kfree(op_stack);
> kfree(inverts);
> + for (i = 0; prog_stack[i].pred; i++)
> + kfree(prog_stack[i].pred);
> kfree(prog_stack);
> return ERR_PTR(ret);
> }

I should have caught this, but thanks to the zero day bot, it found it
first:

kernel/trace/trace_events_filter.c:582:27-31: ERROR: prog_stack is NULL but dereferenced.

I changed the patch with the following:

From dfb4a6f2191a80c8b790117d0ff592fd712d3296 Mon Sep 17 00:00:00 2001
From: Tomas Bortoli <tomasbortoli@gmail.com>
Date: Tue, 28 May 2019 17:43:38 +0200
Subject: [PATCH] tracing: Avoid memory leak in predicate_parse()

In case of errors, predicate_parse() goes to the out_free label
to free memory and to return an error code.

However, predicate_parse() does not free the predicates of the
temporary prog_stack array, thence leaking them.

Link: http://lkml.kernel.org/r/20190528154338.29976-1-tomasbortoli@gmail.com

Cc: stable@vger.kernel.org
Fixes: 80765597bc587 ("tracing: Rewrite filter logic to be simpler and faster")
Reported-by: syzbot+6b8e0fb820e570c59e19@syzkaller.appspotmail.com
Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
[ Added protection around freeing prog_stack[i].pred ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace_events_filter.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index d3e59312ef40..5079d1db3754 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -428,7 +428,7 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
op_stack = kmalloc_array(nr_parens, sizeof(*op_stack), GFP_KERNEL);
if (!op_stack)
return ERR_PTR(-ENOMEM);
- prog_stack = kmalloc_array(nr_preds, sizeof(*prog_stack), GFP_KERNEL);
+ prog_stack = kcalloc(nr_preds, sizeof(*prog_stack), GFP_KERNEL);
if (!prog_stack) {
parse_error(pe, -ENOMEM, 0);
goto out_free;
@@ -579,7 +579,11 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
out_free:
kfree(op_stack);
kfree(inverts);
- kfree(prog_stack);
+ if (prog_stack) {
+ for (i = 0; prog_stack[i].pred; i++)
+ kfree(prog_stack[i].pred);
+ kfree(prog_stack);
+ }
return ERR_PTR(ret);
}

--
2.20.1
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