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authorRichard Weinberger <richard@nod.at>2011-03-23 16:43:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-23 19:46:54 -0700
commitbfdc0b497faa82a0ba2f9dddcf109231dd519fcc (patch)
tree932897262447dacb7158b81209748a295d93e20b /kernel
parentcb16e95fa2996743a6e80a665ed2ed0590bd38cf (diff)
sysctl: restrict write access to dmesg_restrict
When dmesg_restrict is set to 1 CAP_SYS_ADMIN is needed to read the kernel ring buffer. But a root user without CAP_SYS_ADMIN is able to reset dmesg_restrict to 0. This is an issue when e.g. LXC (Linux Containers) are used and complete user space is running without CAP_SYS_ADMIN. A unprivileged and jailed root user can bypass the dmesg_restrict protection. With this patch writing to dmesg_restrict is only allowed when root has CAP_SYS_ADMIN. Signed-off-by: Richard Weinberger <richard@nod.at> Acked-by: Dan Rosenberg <drosenberg@vsecurity.com> Acked-by: Serge E. Hallyn <serge@hallyn.com> Cc: Eric Paris <eparis@redhat.com> Cc: Kees Cook <kees.cook@canonical.com> Cc: James Morris <jmorris@namei.org> Cc: Eugene Teo <eugeneteo@kernel.org> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sysctl.c18
1 files changed, 17 insertions, 1 deletions
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 97ab1690f5ed..c0bb32414b17 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -170,6 +170,11 @@ static int proc_taint(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos);
#endif
+#ifdef CONFIG_PRINTK
+static int proc_dmesg_restrict(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos);
+#endif
+
#ifdef CONFIG_MAGIC_SYSRQ
/* Note: sysrq code uses it's own private copy */
static int __sysrq_enabled = SYSRQ_DEFAULT_ENABLE;
@@ -707,7 +712,7 @@ static struct ctl_table kern_table[] = {
.data = &kptr_restrict,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax,
+ .proc_handler = proc_dmesg_restrict,
.extra1 = &zero,
.extra2 = &two,
},
@@ -2394,6 +2399,17 @@ static int proc_taint(struct ctl_table *table, int write,
return err;
}
+#ifdef CONFIG_PRINTK
+static int proc_dmesg_restrict(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ if (write && !capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+}
+#endif
+
struct do_proc_dointvec_minmax_conv_param {
int *min;
int *max;