linux-kernel - [PATCH v2] Uprobes: Fix kernel oops with delayed_uprobe

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Message-Id: <20181205033423.26242-1-ravi.bangoria@linux.ibm.com>
Date:   Wed,  5 Dec 2018 09:04:23 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     srikar@...ux.vnet.ibm.com, oleg@...hat.com, rostedt@...dmis.org,
        mhiramat@...nel.org, liu.song.a23@...il.com
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, linux-kernel@...r.kernel.org,
        ananth@...ux.vnet.ibm.com, alexis.berlemont@...il.com,
        naveen.n.rao@...ux.vnet.ibm.com,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux@...linux.org.uk, ralf@...ux-mips.org, paul.burton@...s.com,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: [PATCH v2] Uprobes: Fix kernel oops with delayed_uprobe_remove()

There could be a race between task exit and probe unregister:

  exit_mm()
  mmput()
  __mmput()                     uprobe_unregister()
  uprobe_clear_state()          put_uprobe()
  delayed_uprobe_remove()       delayed_uprobe_remove()

put_uprobe() is calling delayed_uprobe_remove() without taking
delayed_uprobe_lock and thus the race sometimes results in a
kernel crash. Fix this by taking delayed_uprobe_lock before
calling delayed_uprobe_remove() from put_uprobe().

Detailed crash log can be found at:
  https://lkml.org/lkml/2018/11/1/1244

Reported-by: syzbot+cb1fb754b771caca0a88@...kaller.appspotmail.com
Fixes: 1cc33161a83d ("uprobes: Support SDT markers having reference count (semaphore)")
Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
---
 kernel/events/uprobes.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 322e97bbb437..abbd8da9ac21 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -572,7 +572,9 @@ static void put_uprobe(struct uprobe *uprobe)
 		 * gets called, we don't get a chance to remove uprobe from
 		 * delayed_uprobe_list from remove_breakpoint(). Do it here.
 		 */
+		mutex_lock(&delayed_uprobe_lock);
 		delayed_uprobe_remove(uprobe, NULL);
+		mutex_unlock(&delayed_uprobe_lock);
 		kfree(uprobe);
 	}
 }
-- 
2.19.2