lkml.org 
[lkml]   [2019]   [Jan]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 3/8] ocfs2: change snprintf to scnprintf for possible overflow
On Sat, Jan 12, 2019 at 7:28 AM Willy Tarreau <w@1wt.eu> wrote:
>
> From: Silvio Cesare <silvio.cesare@gmail.com>
>
> Change snprintf to scnprintf. There are generally two cases where using
> snprintf causes problems.
>
> 1) Uses of size += snprintf(buf, SIZE - size, fmt, ...)
> In this case, if snprintf would have written more characters than what the
> buffer size (SIZE) is, then size will end up larger than SIZE. In later
> uses of snprintf, SIZE - size will result in a negative number, leading
> to problems. Note that size might already be too large by using
> size = snprintf before the code reaches a case of size += snprintf.
>
> 2) If size is ultimately used as a length parameter for a copy back to user
> space, then it will potentially allow for a buffer overflow and information
> disclosure when size is greater than SIZE. When the size is used to index
> the buffer directly, we can have memory corruption. This also means when
> size = snprintf... is used, it may also cause problems since size may become
> large. Copying to userspace is mitigated by the HARDENED_USERCOPY kernel
> configuration.
>
> The solution to these issues is to use scnprintf which returns the number of
> characters actually written to the buffer, so the size variable will never
> exceed SIZE.
>
> Signed-off-by: Silvio Cesare <silvio.cesare@gmail.com>
> Cc: Mark Fasheh <mark@fasheh.com>
> Cc: Joel Becker <jlbec@evilplan.org>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Greg KH <greg@kroah.com>
> Signed-off-by: Willy Tarreau <w@1wt.eu>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

>
> ---
> fs/ocfs2/cluster/heartbeat.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
> index 9b2ed62dd638..2a0af0887ba0 100644
> --- a/fs/ocfs2/cluster/heartbeat.c
> +++ b/fs/ocfs2/cluster/heartbeat.c
> @@ -1324,7 +1324,7 @@ static int o2hb_debug_open(struct inode *inode, struct file *file)
>
> case O2HB_DB_TYPE_REGION_NUMBER:
> reg = (struct o2hb_region *)db->db_data;
> - out += snprintf(buf + out, PAGE_SIZE - out, "%d\n",
> + out += scnprintf(buf + out, PAGE_SIZE - out, "%d\n",
> reg->hr_region_num);
> goto done;
>
> @@ -1334,12 +1334,12 @@ static int o2hb_debug_open(struct inode *inode, struct file *file)
> /* If 0, it has never been set before */
> if (lts)
> lts = jiffies_to_msecs(jiffies - lts);
> - out += snprintf(buf + out, PAGE_SIZE - out, "%lu\n", lts);
> + out += scnprintf(buf + out, PAGE_SIZE - out, "%lu\n", lts);
> goto done;
>
> case O2HB_DB_TYPE_REGION_PINNED:
> reg = (struct o2hb_region *)db->db_data;
> - out += snprintf(buf + out, PAGE_SIZE - out, "%u\n",
> + out += scnprintf(buf + out, PAGE_SIZE - out, "%u\n",
> !!reg->hr_item_pinned);
> goto done;
>
> @@ -1348,8 +1348,8 @@ static int o2hb_debug_open(struct inode *inode, struct file *file)
> }
>
> while ((i = find_next_bit(map, db->db_len, i + 1)) < db->db_len)
> - out += snprintf(buf + out, PAGE_SIZE - out, "%d ", i);
> - out += snprintf(buf + out, PAGE_SIZE - out, "\n");
> + out += scnprintf(buf + out, PAGE_SIZE - out, "%d ", i);
> + out += scnprintf(buf + out, PAGE_SIZE - out, "\n");
>
> done:
> i_size_write(inode, out);
> --
> 2.19.2
>


--
Kees Cook

\
 
 \ /
  Last update: 2019-01-15 02:14    [W:0.286 / U:12.540 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site