The patch titled
Subject: shmem: update memory reservation on truncate
has been added to the -mm tree. Its filename is
shmem-update-memory-reservation-on-truncate.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/shmem-update-memory-reservation-on-truncate.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/shmem-update-memory-reservation-on-truncate.patch
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------------------------------------------------------
From: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Subject: 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/<pid>/map_files/... (available if
CONFIG_CHECKPOINT_RESTORE=y) allows that.
This patch adjusts the memory reservation in shmem_setattr().
exploit:
#include <sys/mman.h>
#include <unistd.h>
#include <stdio.h>
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 <koct9i@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff -puN mm/shmem.c~shmem-update-memory-reservation-on-truncate mm/shmem.c
--- a/mm/shmem.c~shmem-update-memory-reservation-on-truncate
+++ a/mm/shmem.c
@@ -149,6 +149,19 @@ static inline void shmem_unacct_size(uns
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 *
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;
}
_
Patches currently in -mm which might be from koct9i@xxxxxxxxx are
origin.patch
mm-memoryc-use-entry-=-access_oncepte-in-handle_pte_fault.patch
shmem-fix-double-uncharge-in-__shmem_file_setup.patch
shmem-update-memory-reservation-on-truncate.patch
mm-catch-memory-commitment-underflow.patch
lib-idr-fix-out-of-bounds-pointer-dereference.patch
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