From: Peter Hurley <peter@hurleysoftware.com>
Date: Fri, 22 Nov 2013 12:16:25 +0000 (-0500)
Subject: n_tty: Fix 4096-byte canonical reads
X-Git-Tag: v3.13-rc2~15^2~7
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c77569d2f3ef7844ee4ac7005a57da6898b302a8;p=pandora-kernel.git

n_tty: Fix 4096-byte canonical reads

Although the maximum allowable canonical line is specified to
be 255 bytes (MAX_CANON), the practical limit has actually been
the size of the line discipline read buffer (N_TTY_BUF_SIZE == 4096).

Commit 32f13521ca68bc624ff6effc77f308a52b038bf0,
n_tty: Line copy to user buffer in canonical mode, limited the
line copy to 4095 bytes. With a completely full line discipline
read buffer and a userspace buffer > 4095, _no_ data was copied,
and the read() syscall returned 0, indicating EOF.

Fix the interval arithmetic to compute the correct number of bytes
to copy to userspace in the range [1..4096].

Cc: <stable@vger.kernel.org> # 3.12.x
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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