fs/ntfs3: prevent infinite loops caused by the next valid being the same

[PATCH] fs/ntfs3: prevent infinite loops caused by the next valid being the same

Posted by Edward Adam Davis 1 month, 1 week ago

When processing valid within the range [valid : pos), if valid cannot
be retrieved correctly, for example, if the retrieved valid value is
always the same, this can trigger a potential infinite loop, similar
to the hung problem reported by syzbot [1].

Adding a check for the valid value within the loop body, and terminating
the loop and returning -EINVAL if the value is the same as the current
value, can prevent this.

[1]
INFO: task syz.4.21:6056 blocked for more than 143 seconds.
Call Trace:
 rwbase_write_lock+0x14f/0x750 kernel/locking/rwbase_rt.c:244
 inode_lock include/linux/fs.h:1027 [inline]
 ntfs_file_write_iter+0xe6/0x870 fs/ntfs3/file.c:1284

Fixes: 4342306f0f0d ("fs/ntfs3: Add file operations and implementation")
Reported-by: syzbot+bcf9e1868c1a0c7e04f1@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bcf9e1868c1a0c7e04f1
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/ntfs3/file.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs3/file.c b/fs/ntfs3/file.c
index 2e7b2e566ebe..04292674f889 100644
--- a/fs/ntfs3/file.c
+++ b/fs/ntfs3/file.c
@@ -1077,8 +1077,12 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 			goto out;
 
 		if (lcn == SPARSE_LCN) {
-			ni->i_valid = valid =
-				frame_vbo + ((u64)clen << sbi->cluster_bits);
+			valid = frame_vbo + ((u64)clen << sbi->cluster_bits);
+			if (ni->i_valid == valid) {
+				err = -EINVAL;
+				goto out;
+			}
+			ni->i_valid = valid;
 			continue;
 		}
 
-- 
2.43.0

Re: [PATCH] fs/ntfs3: prevent infinite loops caused by the next valid being the same

Posted by Konstantin Komarov 3 weeks, 1 day ago

On 12/28/25 04:53, Edward Adam Davis wrote:

> When processing valid within the range [valid : pos), if valid cannot
> be retrieved correctly, for example, if the retrieved valid value is
> always the same, this can trigger a potential infinite loop, similar
> to the hung problem reported by syzbot [1].
>
> Adding a check for the valid value within the loop body, and terminating
> the loop and returning -EINVAL if the value is the same as the current
> value, can prevent this.
>
> [1]
> INFO: task syz.4.21:6056 blocked for more than 143 seconds.
> Call Trace:
>   rwbase_write_lock+0x14f/0x750 kernel/locking/rwbase_rt.c:244
>   inode_lock include/linux/fs.h:1027 [inline]
>   ntfs_file_write_iter+0xe6/0x870 fs/ntfs3/file.c:1284
>
> Fixes: 4342306f0f0d ("fs/ntfs3: Add file operations and implementation")
> Reported-by: syzbot+bcf9e1868c1a0c7e04f1@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=bcf9e1868c1a0c7e04f1
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>   fs/ntfs3/file.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ntfs3/file.c b/fs/ntfs3/file.c
> index 2e7b2e566ebe..04292674f889 100644
> --- a/fs/ntfs3/file.c
> +++ b/fs/ntfs3/file.c
> @@ -1077,8 +1077,12 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   			goto out;
>   
>   		if (lcn == SPARSE_LCN) {
> -			ni->i_valid = valid =
> -				frame_vbo + ((u64)clen << sbi->cluster_bits);
> +			valid = frame_vbo + ((u64)clen << sbi->cluster_bits);
> +			if (ni->i_valid == valid) {
> +				err = -EINVAL;
> +				goto out;
> +			}
> +			ni->i_valid = valid;
>   			continue;
>   		}
>   

Applied to my tree, thanks for the patch.

Regards,
Konstantin