From 9900bb1b6a14558e86ed4435e8a72e36c1190806 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Thu, 26 Jun 2014 10:42:43 +1000 Subject: [PATCH] shmem: update memory reservation on truncate A shared anonymous mapping created without MAP_NORESERVE holds memory reservation for whole range of shmem segment. Usually there is no way to change its size, but /proc//map_files/... (available if CONFIG_CHECKPOINT_RESTORE=y) allows that. This patch adjusts the memory reservation in shmem_setattr(). exploit: #include #include #include int main(int argc, char **argv) { unsigned long addr; char path[100]; /* charge 4KiB */ addr = (unsigned long)mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0); sprintf(path, "/proc/self/map_files/%lx-%lx", addr, addr + 4096); truncate(path, 1 << 30); /* uncharge 1GiB */ } Signed-off-by: Konstantin Khlebnikov Cc: Hugh Dickins Signed-off-by: Andrew Morton --- mm/shmem.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 974064ababcc..5e5d8601c712 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -149,6 +149,19 @@ static inline void shmem_unacct_size(unsigned long flags, loff_t size) vm_unacct_memory(VM_ACCT(size)); } +static inline int shmem_reacct_size(unsigned long flags, + loff_t oldsize, loff_t newsize) +{ + if (!(flags & VM_NORESERVE)) { + if (VM_ACCT(newsize) > VM_ACCT(oldsize)) + return security_vm_enough_memory_mm(current->mm, + VM_ACCT(newsize) - VM_ACCT(oldsize)); + else if (VM_ACCT(newsize) < VM_ACCT(oldsize)) + vm_unacct_memory(VM_ACCT(oldsize) - VM_ACCT(newsize)); + } + return 0; +} + /* * ... whereas tmpfs objects are accounted incrementally as * pages are allocated, in order to allow huge sparse files. @@ -539,6 +552,10 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr) loff_t newsize = attr->ia_size; if (newsize != oldsize) { + error = shmem_reacct_size(SHMEM_I(inode)->flags, + oldsize, newsize); + if (error) + return error; i_size_write(inode, newsize); inode->i_ctime = inode->i_mtime = CURRENT_TIME; } -- 2.39.5