util_lib/elf_info: harden parsing of printk buffer
    
    Resolves: bz2069200
    Upstream: git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
    Conflicts: None
    
    commit f4c59879b830c7d574a953e6ce970ddaf20910d7
    Author: Philipp Rudo <prudo@redhat.com>
    Date:   Wed Mar 23 16:35:36 2022 +0100
    
        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>
    
    Signed-off-by: Philipp Rudo <prudo@redhat.com>