From: Namjae Jeon <linkinjeon@kernel.org>
To: Qianchang Zhao <pioooooooooip@gmail.com>
Cc: Steve French <smfrench@gmail.com>,
linux-cifs@vger.kernel.org, linux-kernel@vger.kernel.org,
Zhitong Liu <liuzhitong1993@gmail.com>
Subject: Re: [PATCH] ksmbd: vfs: fix truncate lock-range check for shrink/grow and avoid size==0 underflow
Date: Sat, 8 Nov 2025 23:46:41 +0900 [thread overview]
Message-ID: <CAKYAXd-R8NGDzQ-GTM67QbCxwJTCMGNhxKBo1a0sm0XBDqftLw@mail.gmail.com> (raw)
In-Reply-To: <20251108123609.382365-1-pioooooooooip@gmail.com>
On Sat, Nov 8, 2025 at 9:36 PM Qianchang Zhao <pioooooooooip@gmail.com> wrote:
>
> ksmbd_vfs_truncate() uses check_lock_range() with arguments that are
> incorrect for shrink, and can underflow when size==0:
>
> - For shrink, the code passed [inode->i_size, size-1], which is reversed.
> - When size==0, "size-1" underflows to -1, so the range becomes
> [old_size, -1], effectively skipping the intended [0, old_size-1].
>
> Fix by:
> - Rejecting negative size with -EINVAL.
> - For shrink (size < old): check [size, old-1].
> - For grow (size > old): check [old, size-1].
> - Skip lock check when size == old.
> - Keep the return value on conflict as -EAGAIN (no noisy pr_err()).
>
> This avoids the size==0 underflow and uses the correct range order,
> preserving byte-range lock semantics.
>
> Reported-by: Qianchang Zhao <pioooooooooip@gmail.com>
> Reported-by: Zhitong Liu <liuzhitong1993@gmail.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Qianchang Zhao <pioooooooooip@gmail.com>
> ---
> fs/smb/server/vfs.c | 28 +++++++++++++++++++---------
> 1 file changed, 19 insertions(+), 9 deletions(-)
>
> diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
> index 891ed2dc2..e7843ec9b 100644
> --- a/fs/smb/server/vfs.c
> +++ b/fs/smb/server/vfs.c
> @@ -825,17 +825,27 @@ int ksmbd_vfs_truncate(struct ksmbd_work *work,
> if (!work->tcon->posix_extensions) {
> struct inode *inode = file_inode(filp);
>
> - if (size < inode->i_size) {
> - err = check_lock_range(filp, size,
> - inode->i_size - 1, WRITE);
> - } else {
> - err = check_lock_range(filp, inode->i_size,
> - size - 1, WRITE);
> + loff_t old = i_size_read(inode);
> + loff_t start = 0, end = -1;
> + bool need_check = false;
> +
> + if (size < 0)
> + return -EINVAL;
There is no case where size variable is negative.
> +
> + if (size < old) {
> + start = size;
> + end = old - 1;
> + need_check = true;
> + } else if (size > old) {
> + start = old;
> + end = size - 1;
> + need_check = true;
> }
>
> - if (err) {
> - pr_err("failed due to lock\n");
> - return -EAGAIN;
> + if (need_check) {
> + err = check_lock_range(filp, start, end, WRITE);
> + if (err)
> + return -EAGAIN;
> }
> }
Can't you just change it like this?
diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 891ed2dc2b73..f96f27c60301 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -828,7 +828,7 @@ int ksmbd_vfs_truncate(struct ksmbd_work *work,
if (size < inode->i_size) {
err = check_lock_range(filp, size,
inode->i_size - 1, WRITE);
- } else {
+ } else if (size > inode->i_size) {
err = check_lock_range(filp, inode->i_size,
size - 1, WRITE);
}
Thanks.
> --
> 2.34.1
>
next prev parent reply other threads:[~2025-11-08 14:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <2025110803-retrace-unnatural-127f@gregkh>
2025-11-08 12:36 ` [PATCH] ksmbd: vfs: fix truncate lock-range check for shrink/grow and avoid size==0 underflow Qianchang Zhao
2025-11-08 14:46 ` Namjae Jeon [this message]
2025-11-08 15:57 ` [PATCH v2] ksmbd: vfs: skip lock-range check on equal size to " Qianchang Zhao
2025-11-09 1:32 ` Namjae Jeon
2025-11-08 16:00 ` [PATCH] ksmbd: vfs: fix truncate lock-range check for shrink/grow and " くさあさ
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