Author: Eric Paris <[EMAIL PROTECTED]>
AuthorDate: Thu Jan 31 15:11:22 2008 -0500
Committer: James Morris <[EMAIL PROTECTED]>
CommitDate: Wed Feb 6 21:39:46 2008 +0800
security: allow Kconfig to set default mmap_min_addr protection
Since it was decided that low memory protection from userspace couldn't
be turned on by default add a Kconfig option to allow users/distros to
set a default at compile time. This value is still tunable after boot
Signed-off-by: Eric Paris <[EMAIL PROTECTED]>
Signed-off-by: James Morris <[EMAIL PROTECTED]>
security/Kconfig | 18 ++++++++++++++++++
security/security.c | 4 +++-
2 files changed, 21 insertions(+), 1 deletions(-)
diff --git a/security/Kconfig b/security/Kconfig
index 25ffe1b..5dfc206 100644
@@ -104,6 +104,24 @@ config SECURITY_ROOTPLUG
If you are unsure how to answer this question, answer N.
+ int "Low address space to protect from user allocation"
+ depends on SECURITY
+ default 0
+ This is the portion of low virtual memory which should be protected
+ from userspace allocation. Keeping a user from writing to low pages
+ can help reduce the impact of kernel NULL pointer bugs.
+ For most users with lots of address space a value of 65536 is
+ reasonable and should cause no problems. Programs which use vm86
+ functionality would either need additional permissions from either
+ the LSM or the capabilities module or have this protection disabled.
+ This value can be changed after boot using the
+ /proc/sys/vm/mmap_min_addr tunable.
diff --git a/security/security.c b/security/security.c
index b6c57a6..d15e56c 100644
@@ -23,7 +23,9 @@ extern struct security_operations dummy_security_ops;
extern void security_fixup_ops(struct security_operations *ops);
struct security_operations *security_ops; /* Initialized to NULL */
-unsigned long mmap_min_addr; /* 0 means no protection */
+/* amount of vm to protect from userspace access */
+unsigned long mmap_min_addr = CONFIG_SECURITY_DEFAULT_MMAP_MIN_ADDR;
static inline int verify(struct security_operations *ops)
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