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  1. 15 5月, 2011 1 次提交
    • L
      fbmem: fix remove_conflicting_framebuffers races · 712f3147
      由 Linus Torvalds 提交于 
      When a register_framebuffer() call results in us removing old
conflicting framebuffers, the new registration_lock doesn't protect that
situation.  And we can't just add the same locking to the function,
because these functions call each other: register_framebuffer() calls
remove_conflicting_framebuffers, which in turn calls
unregister_framebuffer for any conflicting entry.

In order to fix it, this just creates wrapper functions around all three
functions and makes the versions that actually do the work be called
"do_xxx()", leaving just the wrapper that gets the lock and calls the
worker function.

So the rule becomes simply that "do_xxxx()" has to be called with the
lock held, and now do_register_framebuffer() can just call
do_remove_conflicting_framebuffers(), and that in turn can call
_do_unregister_framebuffer(), and there is no deadlock, and we can hold
the registration lock over the whole sequence, fixing the races.

It also makes error cases simpler, and fixes one situation where we
would return from unregister_framebuffer() without releasing the lock,
pointed out by Bruno Prémont.
Tested-by: NBruno Prémont <bonbons@linux-vserver.org>
Tested-by: NAnca Emanuel <anca.emanuel@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      712f3147
  3. 12 5月, 2011 2 次提交
    • L
      fbmem: make read/write/ioctl use the frame buffer at open time · c47747fd
      由 Linus Torvalds 提交于 
      read/write/ioctl on a fbcon file descriptor has traditionally used the
fbcon not when it was opened, but as it was at the time of the call.
That makes no sense, but the lack of sense is much more obvious now that
we properly ref-count the usage - it means that the ref-counting doesn't
actually protect operations we do on the frame buffer.

This changes it to look at the fb_info that we got at open time, but in
order to avoid using a frame buffer long after it has been unregistered,
we do verify that it is still current, and return -ENODEV if not.
Acked-by: NTim Gardner <tim.gardner@canonical.com>
Tested-by: NDaniel J Blueman <daniel.blueman@gmail.com>
Tested-by: NAnca Emanuel <anca.emanuel@gmail.com>
Cc: Bruno Prémont <bonbons@linux-vserver.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Andy Whitcroft <andy.whitcroft@canonical.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c47747fd
    • L
      fbcon: add lifetime refcount to opened frame buffers · 698b3682
      由 Linus Torvalds 提交于 
      This just adds the refcount and the new registration lock logic.  It
does not (for example) actually change the read/write/ioctl routines to
actually use the frame buffer that was opened: those function still end
up alway susing whatever the current frame buffer is at the time of the
call.

Without this, if something holds the frame buffer open over a
framebuffer switch, the close() operation after the switch will access a
fb_info that has been free'd by the unregistering of the old frame
buffer.

(The read/write/ioctl operations will normally not cause problems,
because they will - illogically - pick up the new fbcon instead.  But a
switch that happens just as one of those is going on might see problems
too, the window is just much smaller: one individual op rather than the
whole open-close sequence.)

This use-after-free is apparently fairly easily triggered by the Ubuntu
11.04 boot sequence.
Acked-by: NTim Gardner <tim.gardner@canonical.com>
Tested-by: NDaniel J Blueman <daniel.blueman@gmail.com>
Tested-by: NAnca Emanuel <anca.emanuel@gmail.com>
Cc: Bruno Prémont <bonbons@linux-vserver.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Andy Whitcroft <andy.whitcroft@canonical.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      698b3682
  5. 11 5月, 2011 37 次提交