Messages in this thread | | | Date | Wed, 17 Aug 2022 17:24:10 +0200 | From | Christian Brauner <> | Subject | Re: [PATCH] binderfs: rework superblock destruction |
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On Wed, Aug 17, 2022 at 04:21:11PM +0100, Al Viro wrote: > On Wed, Aug 17, 2022 at 04:51:44PM +0200, Christian Brauner wrote: > > > diff --git a/arch/s390/hypfs/inode.c b/arch/s390/hypfs/inode.c > > index 5c97f48cea91..d7d275ef132f 100644 > > --- a/arch/s390/hypfs/inode.c > > +++ b/arch/s390/hypfs/inode.c > > @@ -329,9 +329,8 @@ static void hypfs_kill_super(struct super_block *sb) > > hypfs_delete_tree(sb->s_root); > > if (sb_info && sb_info->update_file) > > hypfs_remove(sb_info->update_file); > > - kfree(sb->s_fs_info); > > - sb->s_fs_info = NULL; > > kill_litter_super(sb); > > + kfree(sb->s_fs_info); > > UAF, that - *sb gets freed by the time you try to fetch sb->s_fs_info... > Fetch the pointer first, then destroy the object you've fetched it > from, then free what it points to...
Please note the "completely untested" in the draft... ;)
If you want me to, I can turn this into something serious to review.
> > > diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c > > index 4f25015aa534..78a9095e1748 100644 > > --- a/fs/devpts/inode.c > > +++ b/fs/devpts/inode.c > > @@ -509,10 +509,10 @@ static void devpts_kill_sb(struct super_block *sb) > > { > > struct pts_fs_info *fsi = DEVPTS_SB(sb); > > > > + kill_litter_super(sb); > > if (fsi) > > ida_destroy(&fsi->allocated_ptys); > > kfree(fsi); > > - kill_litter_super(sb); > > } > > > > That one's fine. > > > static struct file_system_type devpts_fs_type = { > > diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c > > index bc66d0173e33..bff49294e037 100644 > > --- a/fs/ramfs/inode.c > > +++ b/fs/ramfs/inode.c > > @@ -280,8 +280,10 @@ int ramfs_init_fs_context(struct fs_context *fc) > > > > static void ramfs_kill_sb(struct super_block *sb) > > { > > - kfree(sb->s_fs_info); > > + struct ramfs_fs_info *fsi = sb->s_fs_info; > > + > > kill_litter_super(sb); > > + kfree(fsi); > > } > > Cosmetical, really - see another posting in the same thread. > > > static struct file_system_type ramfs_fs_type = > > diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c > > index 8fcdd494af27..fb1dae422d93 100644 > > --- a/security/selinux/selinuxfs.c > > +++ b/security/selinux/selinuxfs.c > > @@ -96,9 +96,8 @@ static int selinux_fs_info_create(struct super_block *sb) > > return 0; > > } > > > > -static void selinux_fs_info_free(struct super_block *sb) > > +static void selinux_fs_info_free(struct selinux_fs_info *fsi) > > { > > - struct selinux_fs_info *fsi = sb->s_fs_info; > > int i; > > > > if (fsi) { > > @@ -107,8 +106,7 @@ static void selinux_fs_info_free(struct super_block *sb) > > kfree(fsi->bool_pending_names); > > kfree(fsi->bool_pending_values); > > } > > - kfree(sb->s_fs_info); > > - sb->s_fs_info = NULL; > > + kfree(fsi); > > } > > > > #define SEL_INITCON_INO_OFFSET 0x01000000 > > @@ -2180,7 +2178,7 @@ static int sel_fill_super(struct super_block *sb, struct fs_context *fc) > > pr_err("SELinux: %s: failed while creating inodes\n", > > __func__); > > > > - selinux_fs_info_free(sb); > > + selinux_fs_info_free(fsi); > > > > return ret; > > } > > @@ -2202,8 +2200,10 @@ static int sel_init_fs_context(struct fs_context *fc) > > > > static void sel_kill_sb(struct super_block *sb) > > { > > - selinux_fs_info_free(sb); > > + struct selinux_fs_info *fsi = sb->s_fs_info; > > + > > kill_litter_super(sb); > > + selinux_fs_info_free(fsi); > > } > > A real bug, but an incomplete fix - you've just gotten yourself a double-free; > failure in sel_fill_super() has no need to do selinux_fs_info_free() now.
Please note the "completely untested" in the draft... ;)
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