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Message-ID: <20240930095736.63jxu22xfnxrwvar@quack3>
Date: Mon, 30 Sep 2024 11:57:36 +0200
From: Jan Kara <jack@...e.cz>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
jack@...e.cz, linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
yangerkun@...wei.com, Baokun Li <libaokun1@...wei.com>,
Wesley Hershberger <wesley.hershberger@...onical.com>,
Stéphane Graber <stgraber@...raber.org>,
Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>,
Eric Sandeen <sandeen@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] ext4: fix off by one issue in alloc_flex_gd()
On Fri 27-09-24 21:33:29, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
>
> Wesley reported an issue:
>
> ==================================================================
> EXT4-fs (dm-5): resizing filesystem from 7168 to 786432 blocks
> ------------[ cut here ]------------
> kernel BUG at fs/ext4/resize.c:324!
> CPU: 9 UID: 0 PID: 3576 Comm: resize2fs Not tainted 6.11.0+ #27
> RIP: 0010:ext4_resize_fs+0x1212/0x12d0
> Call Trace:
> __ext4_ioctl+0x4e0/0x1800
> ext4_ioctl+0x12/0x20
> __x64_sys_ioctl+0x99/0xd0
> x64_sys_call+0x1206/0x20d0
> do_syscall_64+0x72/0x110
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
> ==================================================================
>
> While reviewing the patch, Honza found that when adjusting resize_bg in
> alloc_flex_gd(), it was possible for flex_gd->resize_bg to be bigger than
> flexbg_size.
>
> The reproduction of the problem requires the following:
>
> o_group = flexbg_size * 2 * n;
> o_size = (o_group + 1) * group_size;
> n_group: [o_group + flexbg_size, o_group + flexbg_size * 2)
> o_size = (n_group + 1) * group_size;
>
> Take n=0,flexbg_size=16 as an example:
>
> last:15
> |o---------------|--------------n-|
> o_group:0 resize to n_group:30
>
> The corresponding reproducer is:
>
> img=test.img
> truncate -s 600M $img
> mkfs.ext4 -F $img -b 1024 -G 16 8M
> dev=`losetup -f --show $img`
> mkdir -p /tmp/test
> mount $dev /tmp/test
> resize2fs $dev 248M
>
> Delete the problematic plus 1 to fix the issue, and add a WARN_ON_ONCE()
> to prevent the issue from happening again.
>
> Reported-by: Wesley Hershberger <wesley.hershberger@...onical.com>
> Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2081231
> Reported-by: Stéphane Graber <stgraber@...raber.org>
> Closes: https://lore.kernel.org/all/20240925143325.518508-1-aleksandr.mikhalitsyn@canonical.com/
> Tested-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> Tested-by: Eric Sandeen <sandeen@...hat.com>
> Fixes: 665d3e0af4d3 ("ext4: reduce unnecessary memory allocation in alloc_flex_gd()")
> Cc: stable@...r.kernel.org
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
> ---
> Changes since v1:
> * Add missing WARN_ON_ONCE().
> * Correct the comment of alloc_flex_gd().
>
> fs/ext4/resize.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> index e04eb08b9060..a2704f064361 100644
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -230,8 +230,8 @@ struct ext4_new_flex_group_data {
> #define MAX_RESIZE_BG 16384
>
> /*
> - * alloc_flex_gd() allocates a ext4_new_flex_group_data with size of
> - * @flexbg_size.
> + * alloc_flex_gd() allocates an ext4_new_flex_group_data that satisfies the
> + * resizing from @o_group to @n_group, its size is typically @flexbg_size.
> *
> * Returns NULL on failure otherwise address of the allocated structure.
> */
> @@ -239,25 +239,27 @@ static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned int flexbg_size,
> ext4_group_t o_group, ext4_group_t n_group)
> {
> ext4_group_t last_group;
> + unsigned int max_resize_bg;
> struct ext4_new_flex_group_data *flex_gd;
>
> flex_gd = kmalloc(sizeof(*flex_gd), GFP_NOFS);
> if (flex_gd == NULL)
> goto out3;
>
> - if (unlikely(flexbg_size > MAX_RESIZE_BG))
> - flex_gd->resize_bg = MAX_RESIZE_BG;
> - else
> - flex_gd->resize_bg = flexbg_size;
> + max_resize_bg = umin(flexbg_size, MAX_RESIZE_BG);
> + flex_gd->resize_bg = max_resize_bg;
>
> /* Avoid allocating large 'groups' array if not needed */
> last_group = o_group | (flex_gd->resize_bg - 1);
> if (n_group <= last_group)
> - flex_gd->resize_bg = 1 << fls(n_group - o_group + 1);
> + flex_gd->resize_bg = 1 << fls(n_group - o_group);
> else if (n_group - last_group < flex_gd->resize_bg)
> - flex_gd->resize_bg = 1 << max(fls(last_group - o_group + 1),
> + flex_gd->resize_bg = 1 << max(fls(last_group - o_group),
> fls(n_group - last_group));
>
> + if (WARN_ON_ONCE(flex_gd->resize_bg > max_resize_bg))
> + flex_gd->resize_bg = max_resize_bg;
> +
> flex_gd->groups = kmalloc_array(flex_gd->resize_bg,
> sizeof(struct ext4_new_group_data),
> GFP_NOFS);
> --
> 2.39.2
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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