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Subject[PATCH] [RFC] Make it easier to harden /proc/
Date
When containers like LXC are used a unprivileged and jailed
root user can still write to critical files in /proc/.
E.g: /proc/sys/kernel/{sysrq, panic, panic_on_oops, ... }

This new restricted attribute makes it possible to protect such
files. When restricted is set to true root needs CAP_SYS_ADMIN
to into the file.

Signed-off-by: Richard Weinberger <richard@nod.at>
---
fs/proc/proc_sysctl.c | 3 +++
include/linux/sysctl.h | 1 +
2 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 8eb2522..cf7f27d 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -149,6 +149,9 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *buf,
if (sysctl_perm(head->root, table, write ? MAY_WRITE : MAY_READ))
goto out;

+ if (write && table->restricted && !capable(CAP_SYS_ADMIN))
+ goto out;
+
/* if that can happen at all, it should be -EINVAL, not -EISDIR */
error = -EINVAL;
if (!table->proc_handler)
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 11684d9..67d6129 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -1018,6 +1018,7 @@ struct ctl_table
void *data;
int maxlen;
mode_t mode;
+ bool restricted; /* CAP_SYS_ADMIN is needed for write access */
struct ctl_table *child;
struct ctl_table *parent; /* Automatically set */
proc_handler *proc_handler; /* Callback for text formatting */
--
1.6.6.1


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