nfsd: Fix vm overcommit crash
PATCH 1/1 nfsd: Fix vm overcommit crash
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. While at it the checks are switched to WARN_ON - we need to know if someone gets current->mm wrong in the other calls but we don't need to crash.
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(-)
include/linux/security.h +1 -0
@@ -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);
mm/mmap.c +2 -1
@@ -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
mm/nommu.c +2 -1
@@ -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
mm/shmem.c +2 -2
@@ -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)
security/security.c +9 -0
@@ -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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