e976dc27f8
GRUB netbuff structure members track 2 different things: the extent of memory allocated for the packet, and the extent of memory currently being worked on. This works out in the structure as follows: nb->head: beginning of the allocation nb->data: beginning of the working data nb->tail: end of the working data nb->end: end of the allocation The head and end pointers are set in grub_netbuff_alloc() and do not change. The data and tail pointers are initialised to point at start of the allocation (that is, head == data == tail initially), and are then manipulated by grub_netbuff_*() functions. Key functions are as follows: - grub_netbuff_put(): "put" more data into the packet - advance nb->tail - grub_netbuff_unput(): trim the tail of the packet - retract nb->tail - grub_netbuff_pull(): "consume" some packet data - advance nb->data - grub_netbuff_reserve(): reserve space for future headers - advance nb->data and nb->tail - grub_netbuff_push(): "un-consume" data to allow headers to be written - retract nb->data Each of those functions does some form of error checking. For example, grub_netbuff_put() does not allow nb->tail to exceed nb->end, and grub_netbuff_push() does not allow nb->data to be before nb->head. However, grub_netbuff_pull()'s error checking is a bit weird. It advances nb->data and checks that it does not exceed nb->end. That allows you to get into the situation where nb->data > nb->tail, which should not be. Make grub_netbuff_pull() check against both nb->tail and nb->end. In theory just checking against ->tail should be sufficient but the extra check should be cheap and seems like good defensive practice. Signed-off-by: Daniel Axtens <dja@axtens.net> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is GRUB 2, the second version of the GRand Unified Bootloader. GRUB 2 is rewritten from scratch to make GNU GRUB cleaner, safer, more robust, more powerful, and more portable. See the file NEWS for a description of recent changes to GRUB 2. See the file INSTALL for instructions on how to build and install the GRUB 2 data and program files. See the file MAINTAINERS for information about the GRUB maintainers, etc. If you found a security vulnerability in the GRUB please check the SECURITY file to get more information how to properly report this kind of bugs to the maintainers. Please visit the official web page of GRUB 2, for more information. The URL is <http://www.gnu.org/software/grub/grub.html>. More extensive documentation is available in the Info manual, accessible using 'info grub' after building and installing GRUB 2. There are a number of important user-visible differences from the first version of GRUB, now known as GRUB Legacy. For a summary, please see: info grub Introduction 'Changes from GRUB Legacy'