util_lib/elf_info: harden parsing of printk buffer

The old printk mechanism (> v3.5.0 and < v5.10.0) had a fixed size
buffer (log_buf) that contains all messages. The location for the next
message is stored in log_next_idx. In case the log_buf runs full
log_next_idx wraps around and starts overwriting old messages at the
beginning of the buffer. The wraparound is denoted by a message with
msg->len == 0.

Following the behavior described above blindly is dangerous as e.g. a
memory corruption could overwrite (parts of) the log_buf. If the
corruption adds a message with msg->len == 0 this leads to an endless
loop when dumping the dmesg. Fix this by verifying that not wrapped
around before when it encounters a message with msg->len == 0.

While at it also verify that the index is within the log_buf and thus
guard against corruptions with msg->len != 0.

The same bug has been reported and fixed in makedumpfile [1].

[1] http://lists.infradead.org/pipermail/kexec/2022-March/024272.html

Signed-off-by: Philipp Rudo <prudo@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

0 files changed, 0 insertions, 0 deletions