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SubjectRe: [PATCH] Restrict unprivileged access to kernel syslog

* Dan Rosenberg <drosenberg@vsecurity.com> wrote:

> The kernel syslog contains debugging information that is often useful
> during exploitation of other vulnerabilities, such as kernel heap
> addresses. Rather than futilely attempt to sanitize hundreds (or
> thousands) of printk statements and simultaneously cripple useful
> debugging functionality, it is far simpler to create an option that
> prevents unprivileged users from reading the syslog.
>
> This patch, loosely based on grsecurity's GRKERNSEC_DMESG, creates the
> dmesg_restrict sysctl. When set to "0", the default, no restrictions
> are enforced. When set to "1", only users with CAP_SYS_ADMIN can read
> the kernel syslog via dmesg(8) or other mechanisms.
>
> Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
> ---
> Documentation/sysctl/kernel.txt | 11 +++++++++++
> include/linux/kernel.h | 1 +
> kernel/printk.c | 2 ++
> kernel/sysctl.c | 9 +++++++++
> security/commoncap.c | 2 ++
> 5 files changed, 25 insertions(+), 0 deletions(-)

> +int dmesg_restrict = 0;

The initialization to zero is implicit, no need to write it out.

Also, it would also be useful to have a CONFIG_SECURITY_RESTRICT_DMESG=y option
introduced by your patch as well, which flag allows a distro or user to disable
unprivileged syslog reading via the kernel config.

Thanks,

Ingo


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