Serial buffer memory leak

[Laurent Pinchart <laurentp@cse-semaphore.com>]

Hi everybody.

Patch c5c34d4862e18ef07c1276d233507f540fb5a532 (tty: flush flip buffer on 
ldisc input queue flush) introduces a race condition which can lead to memory 
leaks.

The problem can be triggered when tcflush() is called when data are being 
pushed to the line discipline driver by flush_to_ldisc().

flush_to_ldisc() releases tty->buf.lock when calling the line discipline 
receive_buf function. At that poing tty_buffer_flush() kicks in and sets both 
tty->buf.head and tty->buf.tail to NULL. When flush_to_ldisc() finishes, it 
restores tty->buf.head but doesn't touch tty->buf.tail. This corrups the 
buffer queue, and the next call to tty_buffer_request_room() will allocate a 
new buffer and overwrite tty->buf.head. The previous buffer is then lost 
forever without being released.

I'm not familiar enough with the tty code to decide what the proper fix should 
be. I'll try to write a patch if someone could point me in the right 
direction.

Please CC me when answering, as I'm not subscribed to the list.

Regards,

-- 
Laurent Pinchart
CSE Semaphore Belgium

Chaussée de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
F +32 (2) 387 42 75
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