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From: Greg KH on 25 May 2010 14:20
2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------
From: Alan Cox <alan(a)redhat.com>

commit 731572d39fcd3498702eda4600db4c43d51e0b26 upstream.

Junjiro R. Okajima reported a problem where knfsd crashes if you are
using it to export shmemfs objects and run strict overcommit. In this
situation the current->mm based modifier to the overcommit goes through a
NULL pointer.

We could simply check for NULL and skip the modifier but we've caught
other real bugs in the past from mm being NULL here - cases where we did
need a valid mm set up (eg the exec bug about a year ago).

To preserve the checks and get the logic we want shuffle the checking
around and add a new helper to the vm_ security wrappers

Also fix a current->mm reference in nommu that should use the passed mm

[akpm(a)linux-foundation.org: coding-style fixes]
[akpm(a)linux-foundation.org: fix build]
Reported-by: Junjiro R. Okajima <hooanon05(a)yahoo.co.jp>
Acked-by: James Morris <jmorris(a)namei.org>
Signed-off-by: Alan Cox <alan(a)redhat.com>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
include/linux/security.h | 6 ++++++
mm/mmap.c | 3 ++-
mm/nommu.c | 3 ++-
mm/shmem.c | 8 ++++----
security/security.c | 9 +++++++++
5 files changed, 23 insertions(+), 6 deletions(-)

--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1590,6 +1590,7 @@ int security_syslog(int type);
int security_settime(struct timespec *ts, struct timezone *tz);
int security_vm_enough_memory(long pages);
int security_vm_enough_memory_mm(struct mm_struct *mm, long pages);
+int security_vm_enough_memory_kern(long pages);
int security_bprm_alloc(struct linux_binprm *bprm);
void security_bprm_free(struct linux_binprm *bprm);
void security_bprm_apply_creds(struct linux_binprm *bprm, int unsafe);
@@ -1824,6 +1825,11 @@ static inline int security_vm_enough_mem
{
return cap_vm_enough_memory(current->mm, pages);
}
+
+static inline int security_vm_enough_memory_kern(long pages)
+{
+ return cap_vm_enough_memory(current->mm, pages);
+}

static inline int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
{
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -178,7 +178,8 @@ int __vm_enough_memory(struct mm_struct

/* Don't let a single process grow too big:
leave 3% of the size of this process for other processes */
- allowed -= mm->total_vm / 32;
+ if (mm)
+ allowed -= mm->total_vm / 32;

/*
* cast `allowed' as a signed long because vm_committed_space
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1432,7 +1432,8 @@ int __vm_enough_memory(struct mm_struct

/* Don't let a single process grow too big:
leave 3% of the size of this process for other processes */
- allowed -= current->mm->total_vm / 32;
+ if (mm)
+ allowed -= mm->total_vm / 32;

/*
* cast `allowed' as a signed long because vm_committed_space
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -163,8 +163,8 @@ static inline struct shmem_sb_info *SHME
*/
static inline int shmem_acct_size(unsigned long flags, loff_t size)
{
- return (flags & VM_ACCOUNT)?
- security_vm_enough_memory(VM_ACCT(size)): 0;
+ return (flags & VM_ACCOUNT) ?
+ security_vm_enough_memory_kern(VM_ACCT(size)) : 0;
}

static inline void shmem_unacct_size(unsigned long flags, loff_t size)
@@ -181,8 +181,8 @@ static inline void shmem_unacct_size(uns
*/
static inline int shmem_acct_block(unsigned long flags)
{
- return (flags & VM_ACCOUNT)?
- 0: security_vm_enough_memory(VM_ACCT(PAGE_CACHE_SIZE));
+ return (flags & VM_ACCOUNT) ?
+ 0 : security_vm_enough_memory_kern(VM_ACCT(PAGE_CACHE_SIZE));
}

static inline void shmem_unacct_blocks(unsigned long flags, long pages)
--- a/security/security.c
+++ b/security/security.c
@@ -195,14 +195,23 @@ int security_settime(struct timespec *ts

int security_vm_enough_memory(long pages)
{
+ WARN_ON(current->mm == NULL);
return security_ops->vm_enough_memory(current->mm, pages);
}

int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
{
+ WARN_ON(mm == NULL);
return security_ops->vm_enough_memory(mm, pages);
}

+int security_vm_enough_memory_kern(long pages)
+{
+ /* If current->mm is a kernel thread then we will pass NULL,
+ for this specific case that is fine */
+ return security_ops->vm_enough_memory(current->mm, pages);
+}
+
int security_bprm_alloc(struct linux_binprm *bprm)
{
return security_ops->bprm_alloc_security(bprm);


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