[PATCH net-next 1/4] mm: provide a mmap_hook infrastructure
From: Eric Dumazet <edumazet@google.com>
Date: 2018-04-20 15:55:54
Also in:
lkml
Subsystem:
filesystems (vfs and infrastructure), memory management, memory management - core, the rest · Maintainers:
Alexander Viro, Christian Brauner, Andrew Morton, David Hildenbrand, Linus Torvalds
When adding tcp mmap() implementation, I forgot that socket lock
had to be taken before current->mm->mmap_sem. syzbot eventually caught
the bug.
This patch provides a new mmap_hook() method in struct file_operations
that might be provided by fs to implement a finer control of whats
to be done before and after do_mmap_pgoff() and/or the mm->mmap_sem
acquire/release.
This is used in following patches by networking and TCP stacks
to solve the lockdep issue, and also allows some preparation
and cleanup work being done before/after mmap_sem is held,
allowing better scalability in multi-threading programs.
Fixes: 93ab6cc69162 ("tcp: implement mmap() for zero copy receive")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <redacted>
---
include/linux/fs.h | 6 ++++++
mm/util.c | 19 ++++++++++++++++++-
2 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 92efaf1f89775f7b017477617dd983c10e0dc4d2..ef3526f84686585678861fc585efea974a69ca55 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h@@ -1698,6 +1698,11 @@ struct block_device_operations; #define NOMMU_VMFLAGS \ (NOMMU_MAP_READ | NOMMU_MAP_WRITE | NOMMU_MAP_EXEC) +enum mmap_hook { + MMAP_HOOK_PREPARE, + MMAP_HOOK_ROLLBACK, + MMAP_HOOK_COMMIT, +}; struct iov_iter;
@@ -1714,6 +1719,7 @@ struct file_operations { long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); long (*compat_ioctl) (struct file *, unsigned int, unsigned long); int (*mmap) (struct file *, struct vm_area_struct *); + int (*mmap_hook) (struct file *, enum mmap_hook); unsigned long mmap_supported_flags; int (*open) (struct inode *, struct file *); int (*flush) (struct file *, fl_owner_t id);
diff --git a/mm/util.c b/mm/util.c
index 1fc4fa7576f762bbbf341f056ca6d0be803a423f..3ddb18ab367f069d5884083e992e999546ccd995 100644
--- a/mm/util.c
+++ b/mm/util.c@@ -350,11 +350,28 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr, ret = security_mmap_file(file, prot, flag); if (!ret) { - if (down_write_killable(&mm->mmap_sem)) + int (*mmap_hook)(struct file *, enum mmap_hook) = NULL; + + if (file) { + mmap_hook = file->f_op->mmap_hook; + + if (mmap_hook) { + ret = mmap_hook(file, MMAP_HOOK_PREPARE); + if (ret) + return ret; + } + } + if (down_write_killable(&mm->mmap_sem)) { + if (mmap_hook) + mmap_hook(file, MMAP_HOOK_ROLLBACK); return -EINTR; + } ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff, &populate, &uf); up_write(&mm->mmap_sem); + if (mmap_hook) + mmap_hook(file, IS_ERR(ret) ? MMAP_HOOK_ROLLBACK : + MMAP_HOOK_COMMIT); userfaultfd_unmap_complete(mm, &uf); if (populate) mm_populate(ret, populate);
--
2.17.0.484.g0c8726318c-goog