Messages in this thread Patch in this message | | | Date | Wed, 22 Oct 2008 13:09:26 +0100 | From | Alan Cox <> | Subject | Re: __vm_enough_memory(), OVERCOMMIT_NEVER, current->mm, kernel thread |
| |
On Wed, 22 Oct 2008 20:26:19 +0900 hooanon05@yahoo.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@redhat.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);
| |