0f3600bf1b
If an existing variable is set with a value whose length is smaller than
the current value, a memory corruption can happen due copying padding '#'
characters outside of the environment block buffer.
This is caused by a wrong calculation of the previous free space position
after moving backward the characters that followed the old variable value.
That position is calculated to fill the remaining of the buffer with the
padding '#' characters. But since isn't calculated correctly, it can lead
to copies outside of the buffer.
The issue can be reproduced by creating a variable with a large value and
then try to set a new value that is much smaller:
$ grub2-editenv --version
grub2-editenv (GRUB) 2.04
$ grub2-editenv env create
$ grub2-editenv env set a="$(for i in {1..500}; do var="b$var"; done; echo $var)"
$ wc -c env
1024 grubenv
$ grub2-editenv env set a="$(for i in {1..50}; do var="b$var"; done; echo $var)"
malloc(): corrupted top size
Aborted (core dumped)
$ wc -c env
0 grubenv
Reported-by: Renaud Métrich <rmetrich@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
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. 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'