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 to do that.
This patch adjust memory reservation in shmem_setattr(). Signed-off-by: Konstantin Khlebnikov <[email protected]> --- 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 */ } --- mm/shmem.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 0aabcbd..a3c49d6 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. @@ -543,6 +556,10 @@ 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; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
