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nfsd: fix vm overcommit crash

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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

[[email protected]: coding-style fixes]
[[email protected]: fix build]
Reported-by: Junjiro R. Okajima <[email protected]>
Acked-by: James Morris <[email protected]>
Signed-off-by: Alan Cox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Alan Cox 2008-10-29 14:01:20 -07:00 • committed by Linus Torvalds
commit 731572d39f
5 changed files with 23 additions and 6 deletions
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3
mm/mmap.c
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@ -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

3
mm/nommu.c
View file

@ -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

8
mm/shmem.c
View file

@ -161,8 +161,8 @@ 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;
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)
@ -179,8 +179,8 @@ 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));
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)