From: Greg Kurz <groug@kaod.org> To: Miklos Szeredi <miklos@szeredi.hu> Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Vivek Goyal <vgoyal@redhat.com>, virtio-fs@redhat.com, Greg Kurz <groug@kaod.org>, mreitz@redhat.com, stable@vger.kernel.org Subject: [PATCH 1/4] fuse: Fix crash in fuse_dentry_automount() error path Date: Tue, 25 May 2021 17:02:27 +0200 [thread overview] Message-ID: <20210525150230.157586-2-groug@kaod.org> (raw) In-Reply-To: <20210525150230.157586-1-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> --- 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: linux-kernel@vger.kernel.org, stable@vger.kernel.org, mreitz@redhat.com, virtio-fs@redhat.com, linux-fsdevel@vger.kernel.org, Vivek Goyal <vgoyal@redhat.com> Subject: [Virtio-fs] [PATCH 1/4] fuse: Fix crash in fuse_dentry_automount() error path Date: Tue, 25 May 2021 17:02:27 +0200 [thread overview] Message-ID: <20210525150230.157586-2-groug@kaod.org> (raw) In-Reply-To: <20210525150230.157586-1-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> --- 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
next prev parent reply other threads:[~2021-05-25 15:03 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-25 15:02 [PATCH 0/4] fuse: Some fixes for submounts Greg Kurz 2021-05-25 15:02 ` [Virtio-fs] " Greg Kurz 2021-05-25 15:02 ` Greg Kurz [this message] 2021-05-25 15:02 ` [Virtio-fs] [PATCH 1/4] fuse: Fix crash in fuse_dentry_automount() error path Greg Kurz 2021-05-27 9:51 ` Max Reitz 2021-05-27 9:51 ` Max Reitz 2021-05-25 15:02 ` [PATCH 2/4] fuse: Fix infinite loop in sget_fc() Greg Kurz 2021-05-25 15:02 ` [Virtio-fs] " Greg Kurz 2021-05-27 10:08 ` Max Reitz 2021-05-27 10:08 ` Max Reitz 2021-05-27 12:31 ` Greg Kurz 2021-05-25 15:02 ` [PATCH 3/4] fuse: Call vfs_get_tree() for submounts Greg Kurz 2021-05-25 15:02 ` [Virtio-fs] " Greg Kurz 2021-05-27 13:24 ` Max Reitz 2021-06-03 7:34 ` Greg Kurz 2021-06-03 7:34 ` Greg Kurz 2021-05-25 15:02 ` [PATCH 4/4] fuse: Make fuse_fill_super_submount() static Greg Kurz 2021-05-25 15:02 ` [Virtio-fs] " Greg Kurz 2021-05-27 13:28 ` Max Reitz
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