An unchecked decrement operation in cl_print() would cause a few
integers to underflow. Where an output terminal's state is stored in
cl_term, the values cl_term->ystart and cl_term->pos.y both underflow.
This can be replicated with the following steps:
1. Get to the GRUB command line
2. Hold down the "d" key (or any key that enters a visible character)
until it fills the entire row
3. Press "HOME" and then press "CTRL-k". This will clear every
character entered in step 2
4. Continuously press "CTRL-y" until the terminal scrolls the original
prompt ("grub> ") passed the terminal's top row. Now, no prompt
should be visible. This step causes cl_term->ystart to underflow
5. Press "HOME" and then "d" (or any visible character). This can have
different visual effects for different systems, but it will always
cause cl_term->pos.y to underflow
On BIOS systems, these underflows cause the output terminal to
completely stop displaying anything. Characters can still be
entered and commands can be run, but nothing will display on the
terminal. From here, you can only get the display working by running
a command to switch the current output terminal to a different type:
terminal_output <OTHER_TERMINAL>
On UEFI systems, these replication steps do not break the output
terminal. Until you press "ENTER", the cursor stops responding to input,
but you can press "ENTER" after step 5 and the command line will
work properly again. This patch is mostly important for BIOS systems
where the output terminal is rendered unusable after the underflows
occur.
This patch adds two checks, one for each variable. It ensures that
cl_term->ystart does not decrement passed 0. It also ensures that
cl_term->pos.y does not get set passed the terminal's bottom row.
When the previously listed replication steps are followed with this
patch, the terminal's cursor will be set to the top row and the command
line is still usable, even on BIOS systems.
Signed-off-by: Ryan Cohen <rcohenprogramming@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This attempts to fix the places where we do the following where
arithmetic_expr may include unvalidated data:
X = grub_malloc(arithmetic_expr);
It accomplishes this by doing the arithmetic ahead of time using grub_add(),
grub_sub(), grub_mul() and testing for overflow before proceeding.
Among other issues, this fixes:
- allocation of integer overflow in grub_video_bitmap_create()
reported by Chris Coulson,
- allocation of integer overflow in grub_png_decode_image_header()
reported by Chris Coulson,
- allocation of integer overflow in grub_squash_read_symlink()
reported by Chris Coulson,
- allocation of integer overflow in grub_ext2_read_symlink()
reported by Chris Coulson,
- allocation of integer overflow in read_section_as_string()
reported by Chris Coulson.
Fixes: CVE-2020-14309, CVE-2020-14310, CVE-2020-14311
Signed-off-by: Peter Jones <pjones@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This modifies most of the places we do some form of:
X = malloc(Y * Z);
to use calloc(Y, Z) instead.
Among other issues, this fixes:
- allocation of integer overflow in grub_png_decode_image_header()
reported by Chris Coulson,
- allocation of integer overflow in luks_recover_key()
reported by Chris Coulson,
- allocation of integer overflow in grub_lvm_detect()
reported by Chris Coulson.
Fixes: CVE-2020-14308
Signed-off-by: Peter Jones <pjones@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
handling to copy the killed characters to the kill buffer as
UCS4 stored as grub_uint32_t rather than as 8-bit characters
stored as char. Eliminates UCS4 truncation and corruption
observed when killing characters with Ctrl-u and yanking them
back with Ctrl-y.
