From eaf06b241b091357e72b76863ba16e89610d31bd Mon Sep 17 00:00:00 2001 From: Dan Rosenberg Date: Thu, 11 Nov 2010 14:05:18 -0800 Subject: Restrict unprivileged access to kernel syslog 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. [akpm@linux-foundation.org: explain the config option in kernel.txt] Signed-off-by: Dan Rosenberg Acked-by: Ingo Molnar Acked-by: Eugene Teo Acked-by: Kees Cook Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- security/commoncap.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'security/commoncap.c') diff --git a/security/commoncap.c b/security/commoncap.c index 5e632b4857e4..04b80f9912bf 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -895,6 +895,8 @@ int cap_syslog(int type, bool from_file) { if (type != SYSLOG_ACTION_OPEN && from_file) return 0; + if (dmesg_restrict && !capable(CAP_SYS_ADMIN)) + return -EPERM; if ((type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER) && !capable(CAP_SYS_ADMIN)) return -EPERM; -- cgit From 12b3052c3ee8f508b2c7ee4ddd63ed03423409d8 Mon Sep 17 00:00:00 2001 From: Eric Paris Date: Mon, 15 Nov 2010 18:36:29 -0500 Subject: capabilities/syslog: open code cap_syslog logic to fix build failure The addition of CONFIG_SECURITY_DMESG_RESTRICT resulted in a build failure when CONFIG_PRINTK=n. This is because the capabilities code which used the new option was built even though the variable in question didn't exist. The patch here fixes this by moving the capabilities checks out of the LSM and into the caller. All (known) LSMs should have been calling the capabilities hook already so it actually makes the code organization better to eliminate the hook altogether. Signed-off-by: Eric Paris Acked-by: James Morris Signed-off-by: Linus Torvalds --- security/commoncap.c | 21 --------------------- 1 file changed, 21 deletions(-) (limited to 'security/commoncap.c') diff --git a/security/commoncap.c b/security/commoncap.c index 04b80f9912bf..64c2ed9c9015 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -27,7 +27,6 @@ #include #include #include -#include /* * If a non-root user executes a setuid-root binary in @@ -883,26 +882,6 @@ error: return error; } -/** - * cap_syslog - Determine whether syslog function is permitted - * @type: Function requested - * @from_file: Whether this request came from an open file (i.e. /proc) - * - * Determine whether the current process is permitted to use a particular - * syslog function, returning 0 if permission is granted, -ve if not. - */ -int cap_syslog(int type, bool from_file) -{ - if (type != SYSLOG_ACTION_OPEN && from_file) - return 0; - if (dmesg_restrict && !capable(CAP_SYS_ADMIN)) - return -EPERM; - if ((type != SYSLOG_ACTION_READ_ALL && - type != SYSLOG_ACTION_SIZE_BUFFER) && !capable(CAP_SYS_ADMIN)) - return -EPERM; - return 0; -} - /** * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted * @mm: The VM space in which the new mapping is to be made -- cgit