[PATCH 3.16 213/410] pipe: fix off-by-one error when checking buffer limits

From: Ben Hutchings
Date: Thu Jun 07 2018 - 10:41:01 EST


3.16.57-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@xxxxxxxxxx>

commit 9903a91c763ecdae333a04a9d89d79d2b8966503 upstream.

With pipe-user-pages-hard set to 'N', users were actually only allowed up
to 'N - 1' buffers; and likewise for pipe-user-pages-soft.

Fix this to allow up to 'N' buffers, as would be expected.

Link: http://lkml.kernel.org/r/20180111052902.14409-5-ebiggers3@xxxxxxxxx
Fixes: b0b91d18e2e9 ("pipe: fix limit checking in pipe_set_size()")
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Acked-by: Willy Tarreau <w@xxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: "Luis R . Rodriguez" <mcgrof@xxxxxxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
fs/pipe.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -593,12 +593,12 @@ static unsigned long account_pipe_buffer

static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
{
- return pipe_user_pages_soft && user_bufs >= pipe_user_pages_soft;
+ return pipe_user_pages_soft && user_bufs > pipe_user_pages_soft;
}

static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
{
- return pipe_user_pages_hard && user_bufs >= pipe_user_pages_hard;
+ return pipe_user_pages_hard && user_bufs > pipe_user_pages_hard;
}

static bool is_unprivileged_user(void)