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Message-Id: <1379317437-28329-1-git-send-email-keescook@chromium.org>
Date: Mon, 16 Sep 2013 00:43:55 -0700
From: Kees Cook <keescook@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: joe@...ches.com, George Spelvin <linux@...izon.com>,
dan.carpenter@...cle.com, viro@...iv.linux.org.uk,
Jan Beulich <JBeulich@...e.com>,
KOSAKI Motohiro <kosaki.motohiro@...il.com>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
akpm@...ux-foundation.org
Subject: [PATCH 0/2] vsprintf: ignore %n again
Whether seq_printf should return void or error, %n still needs to be removed.
As such, instead of changing the seq_file structure and adding instructions
to all callers of seq_printf, just examine seq->count for the callers that
care about how many characters were put into the buffer, as suggested by
George Spelvin. First patch removes all %n usage in favor of checking
seq->count before/after. Second patch makes %n ignore its argument.
Testing shows this all works happily, and everything is still getting
padded correctly:
/proc/consoles:
ttyS0 -W- (EC a) 4:64
netcon0 -W- (E )
/proc/self/maps:
...
01ee7000-01f08000 rw-p 00000000 00:00 0 [heap]
7fdc79bd4000-7fdc79bf6000 r-xp 00000000 fd:01 394247 /lib/x86_64-linux-gnu/libtinfo.so.5.9
...
/proc/net/tcp
sl local_address rem_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode
0: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 2239 1 ffff88007bfd0000 100 0 0 10 0
...
/proc/net/udp
sl local_address rem_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops
12: 0DAAA8C0:D9D1 0100000A:0035 01 00000000:00000000 00:00000000 00000000 0 0 7534 2 ffff880078048000 0
And a test with a %n in a format string shows the warning:
[ 10.693638] ------------[ cut here ]------------
[ 10.693657] WARNING: CPU: 0 PID: 2048 at lib/vsprintf.c:1693 vsnprintf+0x5c1/0x600()
[ 10.693660] Please remove ignored %n in '%n
[ 10.693663] '
...
Fixing the other callers of seq_printf to do the right thing (void or not)
can be separate from this series.
-Kees
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