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Subject[GIT PULL] Uprobes: Fix kernel oops with delayed_uprobe_remove()

Linus,

This is a single commit that fixes a bug in uprobes SDT code
due to a missing mutex protection.


Please pull the latest trace-v4.20-rc5 tree, which can be found at:


git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v4.20-rc5

Tag SHA1: a5405a88026387f237d97b607234db71d91c13e2
Head SHA1: 1aed58e67a6ec1e7a18bfabe8ba6ec2d27c15636


Ravi Bangoria (1):
Uprobes: Fix kernel oops with delayed_uprobe_remove()

----
kernel/events/uprobes.c | 2 ++
1 file changed, 2 insertions(+)
---------------------------
commit 1aed58e67a6ec1e7a18bfabe8ba6ec2d27c15636
Author: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Date: Wed Dec 5 09:04:23 2018 +0530

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:
Link: http://lkml.kernel.org/r/000000000000140c370577db5ece@google.com

Link: http://lkml.kernel.org/r/20181205033423.26242-1-ravi.bangoria@linux.ibm.com

Acked-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Reported-by: syzbot+cb1fb754b771caca0a88@syzkaller.appspotmail.com
Fixes: 1cc33161a83d ("uprobes: Support SDT markers having reference count (semaphore)")
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 96d4bee83489..98b9312ce6b2 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);
}
}
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