linux-kernel - Re: [PATCH] mqueue: correct the type of ro to int

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Message-ID: <i77q2nmmx6jfbqnbgbxlvnz3aauj3pfq6xroo25xslonc4ordy@4cxsxhcrwc3u>
Date: Thu, 4 Dec 2025 15:07:16 +0100
From: Jan Kara <jack@...e.cz>
To: Edward Adam Davis <eadavis@...com>
Cc: syzbot+40f42779048f7476e2e0@...kaller.appspotmail.com, 
	brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH] mqueue: correct the type of ro to int

On Thu 04-12-25 21:16:22, Edward Adam Davis wrote:
> The ro variable, being of type bool, caused the -EROFS return value from
> mnt_want_write() to be implicitly converted to 1. This prevented the file
> from being correctly acquired, thus triggering the issue reported by
> syzbot [1].
> 
> Changing the type of ro to int allows the system to correctly identify
> the reason for the file open failure.
> 
> [1]
> KASAN: null-ptr-deref in range [0x0000000000000040-0x0000000000000047]
> Call Trace:
>  do_mq_open+0x5a0/0x770 ipc/mqueue.c:932
>  __do_sys_mq_open ipc/mqueue.c:945 [inline]
>  __se_sys_mq_open ipc/mqueue.c:938 [inline]
>  __x64_sys_mq_open+0x16a/0x1c0 ipc/mqueue.c:938
> 
> Fixes: f2573685bd0c ("ipc: convert do_mq_open() to FD_ADD()")
> Reported-by: syzbot+40f42779048f7476e2e0@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=40f42779048f7476e2e0
> Tested-by: syzbot+40f42779048f7476e2e0@...kaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@...com>

Ah, indeed. mqueue_file_open() was returning ERR_PTR(1) which was confusing
FD_ADD error handling. Thanks for debugging this! Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  ipc/mqueue.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/ipc/mqueue.c b/ipc/mqueue.c
> index 56e811f9e5fa..90664d26ec07 100644
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
> @@ -893,7 +893,7 @@ static int prepare_open(struct dentry *dentry, int oflag, int ro,
>  }
>  
>  static struct file *mqueue_file_open(struct filename *name,
> -				     struct vfsmount *mnt, int oflag, bool ro,
> +				     struct vfsmount *mnt, int oflag, int ro,
>  				     umode_t mode, struct mq_attr *attr)
>  {
>  	struct dentry *dentry;
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR