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  1. 13 Mar, 2017 28 commits
  3. 11 Mar, 2017 2 commits
    • Marcelo Ricardo Leitner's avatar
      sctp: deny peeloff operation on asocs with threads sleeping on it · 8aee8e6c
      Marcelo Ricardo Leitner authored 
      commit dfcb9f4f upstream.

commit 2dcab598 ("sctp: avoid BUG_ON on sctp_wait_for_sndbuf")
attempted to avoid a BUG_ON call when the association being used for a
sendmsg() is blocked waiting for more sndbuf and another thread did a
peeloff operation on such asoc, moving it to another socket.

As Ben Hutchings noticed, then in such case it would return without
locking back the socket and would cause two unlocks in a row.

Further analysis also revealed that it could allow a double free if the
application managed to peeloff the asoc that is created during the
sendmsg call, because then sctp_sendmsg() would try to free the asoc
that was created only for that call.

This patch takes another approach. It will deny the peeloff operation
if there is a thread sleeping on the asoc, so this situation doesn't
exist anymore. This avoids the issues described above and also honors
the syscalls that are already being handled (it can be multiple sendmsg
calls).

Joint work with Xin Long.

Fixes: 2dcab598 ("sctp: avoid BUG_ON on sctp_wait_for_sndbuf")
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: default avatarMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: default avatarXin Long <lucien.xin@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarJiri Slaby <jslaby@suse.cz>
      8aee8e6c
    • colyli@suse.de's avatar
      md linear: fix a race between linear_add() and linear_congested() · d93cf670
      colyli@suse.de authored 
      commit 03a9e24e upstream.

Recently I receive a bug report that on Linux v3.0 based kerenl, hot add
disk to a md linear device causes kernel crash at linear_congested(). From
the crash image analysis, I find in linear_congested(), mddev->raid_disks
contains value N, but conf->disks[] only has N-1 pointers available. Then
a NULL pointer deference crashes the kernel.

There is a race between linear_add() and linear_congested(), RCU stuffs
used in these two functions cannot avoid the race. Since Linuv v4.0
RCU code is replaced by introducing mddev_suspend().  After checking the
upstream code, it seems linear_congested() is not called in
generic_make_request() code patch, so mddev_suspend() cannot provent it
from being called. The possible race still exists.

Here I explain how the race still exists in current code.  For a machine
has many CPUs, on one CPU, linear_add() is called to add a hard disk to a
md linear device; at the same time on other CPU, linear_congested() is
called to detect whether this md linear device is congested before issuing
an I/O request onto it.

Now I use a possible code execution time sequence to demo how the possible
race happens,

seq    linear_add()                linear_congested()
 0                                 conf=mddev->private
 1   oldconf=mddev->private
 2   mddev->raid_disks++
 3                              for (i=0; i<mddev->raid_disks;i++)
 4                                bdev_get_queue(conf->disks[i].rdev->bdev)
 5   mddev->private=newconf

In linear_add() mddev->raid_disks is increased in time seq 2, and on
another CPU in linear_congested() the for-loop iterates conf->disks[i] by
the increased mddev->raid_disks in time seq 3,4. But conf with one more
element (which is a pointer to struct dev_info type) to conf->disks[] is
not updated yet, accessing its structure member in time seq 4 will cause a
NULL pointer deference fault.

To fix this race, there are 2 parts of modification in the patch,
 1) Add 'int raid_disks' in struct linear_conf, as a copy of
    mddev->raid_disks. It is initialized in linear_conf(), always being
    consistent with pointers number of 'struct dev_info disks[]'. When
    iterating conf->disks[] in linear_congested(), use conf->raid_disks to
    replace mddev->raid_disks in the for-loop, then NULL pointer deference
    will not happen again.
 2) RCU stuffs are back again, and use kfree_rcu() in linear_add() to
    free oldconf memory. Because oldconf may be referenced as mddev->private
    in linear_congested(), kfree_rcu() makes sure that its memory will not
    be released until no one uses it any more.
Also some code comments are added in this patch, to make this modification
to be easier understandable.

This patch can be applied for kernels since v4.0 after commit:
3be260cc ("md/linear: remove rcu protections in favour of
suspend/resume"). But this bug is reported on Linux v3.0 based kernel, for
people who maintain kernels before Linux v4.0, they need to do some back
back port to this patch.

Changelog:
 - V3: add 'int raid_disks' in struct linear_conf, and use kfree_rcu() to
       replace rcu_call() in linear_add().
 - v2: add RCU stuffs by suggestion from Shaohua and Neil.
 - v1: initial effort.
Signed-off-by: default avatarColy Li <colyli@suse.de>
Cc: Shaohua Li <shli@fb.com>
Cc: Neil Brown <neilb@suse.com>
Signed-off-by: default avatarShaohua Li <shli@fb.com>
Signed-off-by: default avatarJiri Slaby <jslaby@suse.cz>
      d93cf670
  5. 06 Mar, 2017 1 commit
  7. 03 Mar, 2017 9 commits
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