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From: Greg Kurz <groug@kaod.org>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: linux-kernel@vger.kernel.org, Max Reitz <mreitz@redhat.com>,
	linux-fsdevel@vger.kernel.org, virtio-fs@redhat.com,
	Vivek Goyal <vgoyal@redhat.com>, Greg Kurz <groug@kaod.org>,
	stable@vger.kernel.org
Subject: [PATCH v2 1/7] fuse: Fix crash in fuse_dentry_automount() error path
Date: Fri,  4 Jun 2021 18:11:50 +0200	[thread overview]
Message-ID: <20210604161156.408496-2-groug@kaod.org> (raw)
In-Reply-To: <20210604161156.408496-1-groug@kaod.org>

If fuse_fill_super_submount() returns an error, the error path
triggers a crash:

[   26.206673] BUG: kernel NULL pointer dereference, address: 0000000000000000
[...]
[   26.226362] RIP: 0010:__list_del_entry_valid+0x25/0x90
[...]
[   26.247938] Call Trace:
[   26.248300]  fuse_mount_remove+0x2c/0x70 [fuse]
[   26.248892]  virtio_kill_sb+0x22/0x160 [virtiofs]
[   26.249487]  deactivate_locked_super+0x36/0xa0
[   26.250077]  fuse_dentry_automount+0x178/0x1a0 [fuse]

The crash happens because fuse_mount_remove() assumes that the FUSE
mount was already added to list under the FUSE connection, but this
only done after fuse_fill_super_submount() has returned success.

This means that until fuse_fill_super_submount() has returned success,
the FUSE mount isn't actually owned by the superblock. We should thus
reclaim ownership by clearing sb->s_fs_info, which will skip the call
to fuse_mount_remove(), and perform rollback, like virtio_fs_get_tree()
already does for the root sb.

Fixes: bf109c64040f ("fuse: implement crossmounts")
Cc: mreitz@redhat.com
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 fs/fuse/dir.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 1b6c001a7dd1..01559061cbfb 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -339,8 +339,12 @@ static struct vfsmount *fuse_dentry_automount(struct path *path)
 
 	/* Initialize superblock, making @mp_fi its root */
 	err = fuse_fill_super_submount(sb, mp_fi);
-	if (err)
+	if (err) {
+		fuse_conn_put(fc);
+		kfree(fm);
+		sb->s_fs_info = NULL;
 		goto out_put_sb;
+	}
 
 	sb->s_flags |= SB_ACTIVE;
 	fsc->root = dget(sb->s_root);
-- 
2.31.1


WARNING: multiple messages have this Message-ID (diff)
From: Greg Kurz <groug@kaod.org>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org,
	virtio-fs@redhat.com, linux-fsdevel@vger.kernel.org,
	Max Reitz <mreitz@redhat.com>, Vivek Goyal <vgoyal@redhat.com>
Subject: [Virtio-fs] [PATCH v2 1/7] fuse: Fix crash in fuse_dentry_automount() error path
Date: Fri,  4 Jun 2021 18:11:50 +0200	[thread overview]
Message-ID: <20210604161156.408496-2-groug@kaod.org> (raw)
In-Reply-To: <20210604161156.408496-1-groug@kaod.org>

If fuse_fill_super_submount() returns an error, the error path
triggers a crash:

[   26.206673] BUG: kernel NULL pointer dereference, address: 0000000000000000
[...]
[   26.226362] RIP: 0010:__list_del_entry_valid+0x25/0x90
[...]
[   26.247938] Call Trace:
[   26.248300]  fuse_mount_remove+0x2c/0x70 [fuse]
[   26.248892]  virtio_kill_sb+0x22/0x160 [virtiofs]
[   26.249487]  deactivate_locked_super+0x36/0xa0
[   26.250077]  fuse_dentry_automount+0x178/0x1a0 [fuse]

The crash happens because fuse_mount_remove() assumes that the FUSE
mount was already added to list under the FUSE connection, but this
only done after fuse_fill_super_submount() has returned success.

This means that until fuse_fill_super_submount() has returned success,
the FUSE mount isn't actually owned by the superblock. We should thus
reclaim ownership by clearing sb->s_fs_info, which will skip the call
to fuse_mount_remove(), and perform rollback, like virtio_fs_get_tree()
already does for the root sb.

Fixes: bf109c64040f ("fuse: implement crossmounts")
Cc: mreitz@redhat.com
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 fs/fuse/dir.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 1b6c001a7dd1..01559061cbfb 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -339,8 +339,12 @@ static struct vfsmount *fuse_dentry_automount(struct path *path)
 
 	/* Initialize superblock, making @mp_fi its root */
 	err = fuse_fill_super_submount(sb, mp_fi);
-	if (err)
+	if (err) {
+		fuse_conn_put(fc);
+		kfree(fm);
+		sb->s_fs_info = NULL;
 		goto out_put_sb;
+	}
 
 	sb->s_flags |= SB_ACTIVE;
 	fsc->root = dget(sb->s_root);
-- 
2.31.1


  reply	other threads:[~2021-06-04 16:12 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-04 16:11 [PATCH v2 0/7] fuse: Some fixes for submounts Greg Kurz
2021-06-04 16:11 ` [Virtio-fs] " Greg Kurz
2021-06-04 16:11 ` Greg Kurz [this message]
2021-06-04 16:11   ` [Virtio-fs] [PATCH v2 1/7] fuse: Fix crash in fuse_dentry_automount() error path Greg Kurz
2021-06-04 16:11 ` [PATCH v2 2/7] fuse: Fix crash if superblock of submount gets killed early Greg Kurz
2021-06-04 16:11   ` [Virtio-fs] " Greg Kurz
2021-06-08 15:08   ` Max Reitz
2021-06-08 15:08     ` [Virtio-fs] " Max Reitz
2021-06-04 16:11 ` [PATCH v2 3/7] fuse: Fix infinite loop in sget_fc() Greg Kurz
2021-06-04 16:11   ` [Virtio-fs] " Greg Kurz
2021-06-08 15:12   ` Max Reitz
2021-06-08 15:12     ` [Virtio-fs] " Max Reitz
2021-06-04 16:11 ` [PATCH v2 4/7] fuse: Add dedicated filesystem context ops for submounts Greg Kurz
2021-06-04 16:11   ` [Virtio-fs] " Greg Kurz
2021-06-08 15:25   ` Max Reitz
2021-06-08 15:25     ` [Virtio-fs] " Max Reitz
2021-06-04 16:11 ` [PATCH v2 5/7] fuse: Call vfs_get_tree() " Greg Kurz
2021-06-04 16:11   ` [Virtio-fs] " Greg Kurz
2021-06-08 15:40   ` Max Reitz
2021-06-08 15:40     ` [Virtio-fs] " Max Reitz
2021-06-04 16:11 ` [PATCH v2 6/7] fuse: Switch to fc_mount() " Greg Kurz
2021-06-04 16:11   ` [Virtio-fs] " Greg Kurz
2021-06-08 15:51   ` Max Reitz
2021-06-08 15:51     ` [Virtio-fs] " Max Reitz
2021-06-09  7:45     ` Greg Kurz
2021-06-09  7:45       ` [Virtio-fs] " Greg Kurz
2021-06-11 14:44       ` Miklos Szeredi
2021-06-11 14:44         ` [Virtio-fs] " Miklos Szeredi
2021-06-04 16:11 ` [PATCH v2 7/7] fuse: Make fuse_fill_super_submount() static Greg Kurz
2021-06-04 16:11   ` [Virtio-fs] " Greg Kurz
2021-06-08 15:52 ` [PATCH v2 0/7] fuse: Some fixes for submounts Max Reitz
2021-06-08 15:52   ` [Virtio-fs] " Max Reitz
2021-06-09  7:46   ` Greg Kurz
2021-06-09  7:46     ` [Virtio-fs] " Greg Kurz

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