Re: [PATCH] qnx4: fix to avoid panic due to buffer overflow

From: Ronald Monthero
Date: Sat Nov 18 2023 - 03:51:46 EST


Thank you Kees and Anders, Cheers

BR,
Ronald

On Fri, Nov 17, 2023 at 4:26 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Thu, Nov 16, 2023 at 05:48:20PM +0100, Anders Larsen wrote:
> > On 2023-11-16 15:58 Kees Cook wrote:
> > > if ((de->di_status & QNX4_FILE_LINK) == QNX4_FILE_LINK) {
> > > lnk = (struct qnx4_link_info *) de;
> > >
> > > It seems that entries may be either struct qnx4_inode_entry or struct
> > > qnx4_link_info but it's not captured in a union.
> > >
> > > This needs to be fixed by not lying to the compiler about what is there.
> > >
> > > How about this?
> >
> > > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > > index 8d72221735d7..3cd20065bcfa 100644
> > > --- a/fs/qnx4/namei.c
> > > +++ b/fs/qnx4/namei.c
> > > @@ -26,31 +26,39 @@
> > > static int qnx4_match(int len, const char *name,
> > > struct buffer_head *bh, unsigned long *offset)
> > > {
> > > - struct qnx4_inode_entry *de;
> > > - int namelen, thislen;
> > > + union qnx4_dir_entry *de;
> > > + char *entry_fname;
> > > + int entry_len, entry_max_len;
> > >
> > > if (bh == NULL) {
> > > printk(KERN_WARNING "qnx4: matching unassigned buffer !
> > \n");
> > > return 0;
> > > }
> > > - de = (struct qnx4_inode_entry *) (bh->b_data + *offset);
> > > + de = (union qnx4_dir_entry *) (bh->b_data + *offset);
> > > *offset += QNX4_DIR_ENTRY_SIZE;
> > > - if ((de->di_status & QNX4_FILE_LINK) != 0) {
> > > - namelen = QNX4_NAME_MAX;
> > > - } else {
> > > - namelen = QNX4_SHORT_NAME_MAX;
> > > - }
> > > - thislen = strlen( de->di_fname );
> > > - if ( thislen > namelen )
> > > - thislen = namelen;
> > > - if (len != thislen) {
> > > +
> > > + switch (de->inode.di_status) {
> > > + case QNX4_FILE_LINK:
> > > + entry_fname = de->link.dl_fname;
> > > + entry_max_len = sizeof(de->link.dl_fname);
> > > + break;
> > > + case QNX4_FILE_USED:
> > > + entry_fname = de->inode.di_fname;
> > > + entry_max_len = sizeof(de->inode.di_fname);
> > > + break;
> > > + default:
> > > return 0;
> > > }
> >
> > The switch won't work since the _status field is a bit-field, so we should
> > rather reuse the similar union-logic already present in fs/qnx4/dir.c
>
> Ah, okay, LINK and USED might both be there. And perfect, yes, it looks
> like the union qnx4_directory_entry in fs/qnx4/dir.c would be perfect.
>
> -Kees
>
> > > - if (strncmp(name, de->di_fname, len) == 0) {
> > > - if ((de->di_status & (QNX4_FILE_USED|QNX4_FILE_LINK)) !
> > = 0) {
> > > - return 1;
> > > - }
> > > - }
> > > +
> > > + /* Directory entry may not be %NUL-terminated. */
> > > + entry_len = strnlen(entry_fname, entry_max_len);
> > > +
> > > + if (len != entry_len)
> > > + return 0;
> > > +
> > > + if (strncmp(name, entry_fname, len) == 0)
> > > + return 1;
> > > +
> > > return 0;
> > > }
> > >
> > > diff --git a/include/uapi/linux/qnx4_fs.h b/include/uapi/linux/qnx4_fs.h
> > > index 31487325d265..e033dbe1e009 100644
> > > --- a/include/uapi/linux/qnx4_fs.h
> > > +++ b/include/uapi/linux/qnx4_fs.h
> > > @@ -68,6 +68,13 @@ struct qnx4_link_info {
> > > __u8 dl_status;
> > > };
> > >
> > > +union qnx4_dir_entry {
> > > + struct qnx4_inode_entry inode;
> > > + struct qnx4_link_info link;
> > > +};
> > > +_Static_assert(offsetof(struct qnx4_inode_entry, di_status) ==
> > > + offsetof(struct qnx4_link_info, dl_status));
> > > +
> > > struct qnx4_xblk {
> > > __le32 xblk_next_xblk;
> > > __le32 xblk_prev_xblk;
> >
> >
> >
> >
>
> --
> Kees Cook