[PATCH] ksmbd: vfs: fix truncate lock-range check for shrink/grow and avoid size==0 underflow

[PATCH] ksmbd: vfs: fix truncate lock-range check for shrink/grow and avoid size==0 underflow

[Qianchang Zhao]

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;
+
+		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;
 		}
 	}
-- 
2.34.1

Re: [PATCH] ksmbd: vfs: fix truncate lock-range check for shrink/grow and avoid size==0 underflow

[Namjae Jeon]

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
>

[PATCH v2] ksmbd: vfs: skip lock-range check on equal size to avoid size==0 underflow

[Qianchang Zhao]

When size equals the current i_size (including 0), the code used to call
check_lock_range(filp, i_size, size - 1, WRITE), which computes `size - 1`
and can underflow for size==0. Skip the equal case.

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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 891ed2dc2..d068b78a3 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);
 		}
-- 
2.34.1

Re: [PATCH v2] ksmbd: vfs: skip lock-range check on equal size to avoid size==0 underflow

[Namjae Jeon]

On Sun, Nov 9, 2025 at 12:57 AM Qianchang Zhao <pioooooooooip@gmail.com> wrote:
>
> When size equals the current i_size (including 0), the code used to call
> check_lock_range(filp, i_size, size - 1, WRITE), which computes `size - 1`
> and can underflow for size==0. Skip the equal case.
>
> 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>
Applied it to #ksmbd-for-next-next.
Thanks!

Re: [PATCH] ksmbd: vfs: fix truncate lock-range check for shrink/grow and avoid size==0 underflow

[くさあさ]

Thanks for the guidance — I’ve sent v2 patch.
Best regards,
Qianchang

On Sat, Nov 8, 2025 at 11:46 PM Namjae Jeon <linkinjeon@kernel.org> wrote:
>
> 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
> >