linux-kernel - Re: [syzbot] [fs?] [mm?] WARNING in path

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Message-ID: <202509301457.30490A014C@keescook>
Date: Tue, 30 Sep 2025 15:04:22 -0700
From: Kees Cook <kees@...nel.org>
To: syzbot <syzbot+a9391462075ffb9f77c6@...kaller.appspotmail.com>
Cc: brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [syzbot] [fs?] [mm?] WARNING in path_noexec (2)

On Tue, Sep 30, 2025 at 01:17:34PM -0700, syzbot wrote:
> Reported-by: syzbot+a9391462075ffb9f77c6@...kaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 6000 at fs/exec.c:119 path_noexec+0x1af/0x200 fs/exec.c:118

Christian, this is:

bool path_noexec(const struct path *path)
{
        /* If it's an anonymous inode make sure that we catch any shenanigans. */
        VFS_WARN_ON_ONCE(IS_ANON_FILE(d_inode(path->dentry)) &&
                         !(path->mnt->mnt_sb->s_iflags & SB_I_NOEXEC));
        return (path->mnt->mnt_flags & MNT_NOEXEC) ||
               (path->mnt->mnt_sb->s_iflags & SB_I_NOEXEC);
}

> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13e5fd6f980000

I think is from the created fd_dma_buf. I expect this would fix it:


diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 2bcf9ceca997..6e2ab1a4560d 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -189,6 +189,8 @@ static int dma_buf_fs_init_context(struct fs_context *fc)
 {
 	struct pseudo_fs_context *ctx;
 
+	fc->s_iflags |= SB_I_NOEXEC;
+	fc->s_iflags |= SB_I_NODEV;
 	ctx = init_pseudo(fc, DMA_BUF_MAGIC);
 	if (!ctx)
 		return -ENOMEM;


Which reminds me, this still isn't landed either for secretmem:
https://lore.kernel.org/all/20250707171735.GE1880847@ZenIV/

-- 
Kees Cook