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Message-ID: <20081022130926.44540b03@lxorguk.ukuu.org.uk>
Date: Wed, 22 Oct 2008 13:09:26 +0100
From: Alan Cox <alan@...rguk.ukuu.org.uk>
To: hooanon05@...oo.co.jp
Cc: linux-kernel@...r.kernel.org
Subject: Re: __vm_enough_memory(), OVERCOMMIT_NEVER, current->mm, kernel
thread
On Wed, 22 Oct 2008 20:26:19 +0900
hooanon05@...oo.co.jp wrote:
>
> Alan Cox:
> > No - the shmem routine would use vm_enough_memory_fs which wouldn't care
> > if current->mm is NULL, but the others would check.
>
> Unfortunately I cannot imagine what new vm_enough_memory_fs() will be.
> Would you show me its draft or pseudo code?
This is the patch I propose:
nfsd: Fix vm overcommit crash
From: Alan Cox <alan@...hat.com>
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
---
include/linux/security.h | 1 +
mm/mmap.c | 3 ++-
mm/nommu.c | 3 ++-
mm/shmem.c | 4 ++--
security/security.c | 9 +++++++++
5 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/include/linux/security.h b/include/linux/security.h
index f5c4a51..a2b8430 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1585,6 +1585,7 @@ 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);
diff --git a/mm/mmap.c b/mm/mmap.c
index 74f4d15..de14ac2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -175,7 +175,8 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
/* 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
diff --git a/mm/nommu.c b/mm/nommu.c
index 2696b24..7695dc8 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1454,7 +1454,8 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
/* 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
diff --git a/mm/shmem.c b/mm/shmem.c
index d38d7e6..1677b3e 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -162,7 +162,7 @@ static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
static inline int shmem_acct_size(unsigned long flags, loff_t size)
{
return (flags & VM_ACCOUNT)?
- security_vm_enough_memory(VM_ACCT(size)): 0;
+ security_vm_enough_memory_kern(VM_ACCT(size)): 0;
}
static inline void shmem_unacct_size(unsigned long flags, loff_t size)
@@ -180,7 +180,7 @@ static inline void shmem_unacct_size(unsigned long flags, loff_t size)
static inline int shmem_acct_block(unsigned long flags)
{
return (flags & VM_ACCOUNT)?
- 0: security_vm_enough_memory(VM_ACCT(PAGE_CACHE_SIZE));
+ 0: security_vm_enough_memory_kern(VM_ACCT(PAGE_CACHE_SIZE));
}
static inline void shmem_unacct_blocks(unsigned long flags, long pages)
diff --git a/security/security.c b/security/security.c
index 255b085..c0acfa7 100644
--- a/security/security.c
+++ b/security/security.c
@@ -198,14 +198,23 @@ int security_settime(struct timespec *ts, struct timezone *tz)
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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