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authorDavid Herrmann <dh.herrmann@gmail.com>2014-08-08 21:25:25 (GMT)
committerMaciej Wereski <m.wereski@partner.samsung.com>2014-12-29 08:31:35 (GMT)
commitf5eb589a8cff825e57d6cb42d84c9ae61f2e1baf (patch)
treebbf7ed91762f0dcfabe0e278901d4270f6d93367
parent5988dd09c4983bed7c2671446de5715a63036bb3 (diff)
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mm: allow drivers to prevent new writable mappingsrefs/changes/04/32904/1
This patch (of 6): The i_mmap_writable field counts existing writable mappings of an address_space. To allow drivers to prevent new writable mappings, make this counter signed and prevent new writable mappings if it is negative. This is modelled after i_writecount and DENYWRITE. This will be required by the shmem-sealing infrastructure to prevent any new writable mappings after the WRITE seal has been set. In case there exists a writable mapping, this operation will fail with EBUSY. Note that we rely on the fact that iff you already own a writable mapping, you can increase the counter without using the helpers. This is the same that we do for i_writecount. Signed-off-by: David Herrmann <dh.herrmann@gmail.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ryan Lortie <desrt@desrt.ca> Cc: Lennart Poettering <lennart@poettering.net> Cc: Daniel Mack <zonque@gmail.com> Cc: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Change-Id: If33fdcedbcf202ab177c4e21afc7eec261088a8b Origin: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4bb5f5d9395bc112d93a134d8f5b05611eddc9c0 Backported-by: Maciej Wereski <m.wereski@partner.samsung.com> Signed-off-by: Maciej Wereski <m.wereski@partner.samsung.com>
-rw-r--r--fs/inode.c1
-rw-r--r--include/linux/fs.h29
-rw-r--r--kernel/fork.c2
-rw-r--r--mm/mmap.c30
-rw-r--r--mm/swap_state.c1
5 files changed, 54 insertions, 9 deletions
diff --git a/fs/inode.c b/fs/inode.c
index 1b300a0..7216a0f 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -164,6 +164,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
mapping->a_ops = &empty_aops;
mapping->host = inode;
mapping->flags = 0;
+ atomic_set(&mapping->i_mmap_writable, 0);
mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
mapping->private_data = NULL;
mapping->backing_dev_info = &default_backing_dev_info;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 310e70f..1924260 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -407,7 +407,7 @@ struct address_space {
struct inode *host; /* owner: inode, block_device */
struct radix_tree_root page_tree; /* radix tree of all pages */
spinlock_t tree_lock; /* and lock protecting it */
- unsigned int i_mmap_writable;/* count VM_SHARED mappings */
+ atomic_t i_mmap_writable;/* count VM_SHARED mappings */
struct rb_root i_mmap; /* tree of private and shared mappings */
struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */
struct mutex i_mmap_mutex; /* protect tree, count, list */
@@ -489,10 +489,35 @@ static inline int mapping_mapped(struct address_space *mapping)
* Note that i_mmap_writable counts all VM_SHARED vmas: do_mmap_pgoff
* marks vma as VM_SHARED if it is shared, and the file was opened for
* writing i.e. vma may be mprotected writable even if now readonly.
+ *
+ * If i_mmap_writable is negative, no new writable mappings are allowed. You
+ * can only deny writable mappings, if none exists right now.
*/
static inline int mapping_writably_mapped(struct address_space *mapping)
{
- return mapping->i_mmap_writable != 0;
+ return atomic_read(&mapping->i_mmap_writable) > 0;
+}
+
+static inline int mapping_map_writable(struct address_space *mapping)
+{
+ return atomic_inc_unless_negative(&mapping->i_mmap_writable) ?
+ 0 : -EPERM;
+}
+
+static inline void mapping_unmap_writable(struct address_space *mapping)
+{
+ atomic_dec(&mapping->i_mmap_writable);
+}
+
+static inline int mapping_deny_writable(struct address_space *mapping)
+{
+ return atomic_dec_unless_positive(&mapping->i_mmap_writable) ?
+ 0 : -EBUSY;
+}
+
+static inline void mapping_allow_writable(struct address_space *mapping)
+{
+ atomic_inc(&mapping->i_mmap_writable);
}
/*
diff --git a/kernel/fork.c b/kernel/fork.c
index 514dbc4..219a0fc 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -422,7 +422,7 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
atomic_dec(&inode->i_writecount);
mutex_lock(&mapping->i_mmap_mutex);
if (tmp->vm_flags & VM_SHARED)
- mapping->i_mmap_writable++;
+ atomic_inc(&mapping->i_mmap_writable);
flush_dcache_mmap_lock(mapping);
/* insert tmp into the share list, just after mpnt */
if (unlikely(tmp->vm_flags & VM_NONLINEAR))
diff --git a/mm/mmap.c b/mm/mmap.c
index f97c319..f49248b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -213,7 +213,7 @@ static void __remove_shared_vm_struct(struct vm_area_struct *vma,
if (vma->vm_flags & VM_DENYWRITE)
atomic_inc(&file_inode(file)->i_writecount);
if (vma->vm_flags & VM_SHARED)
- mapping->i_mmap_writable--;
+ mapping_unmap_writable(mapping);
flush_dcache_mmap_lock(mapping);
if (unlikely(vma->vm_flags & VM_NONLINEAR))
@@ -614,7 +614,7 @@ static void __vma_link_file(struct vm_area_struct *vma)
if (vma->vm_flags & VM_DENYWRITE)
atomic_dec(&file_inode(file)->i_writecount);
if (vma->vm_flags & VM_SHARED)
- mapping->i_mmap_writable++;
+ atomic_inc(&mapping->i_mmap_writable);
flush_dcache_mmap_lock(mapping);
if (unlikely(vma->vm_flags & VM_NONLINEAR))
@@ -1550,6 +1550,17 @@ munmap_back:
if (error)
goto free_vma;
}
+ if (vm_flags & VM_SHARED) {
+ error = mapping_map_writable(file->f_mapping);
+ if (error)
+ goto allow_write_and_free_vma;
+ }
+
+ /* ->mmap() can change vma->vm_file, but must guarantee that
+ * vma_link() below can deny write-access if VM_DENYWRITE is set
+ * and map writably if VM_SHARED is set. This usually means the
+ * new file must not have been exposed to user-space, yet.
+ */
vma->vm_file = get_file(file);
error = file->f_op->mmap(file, vma);
if (error)
@@ -1592,8 +1603,12 @@ munmap_back:
vma_link(mm, vma, prev, rb_link, rb_parent);
/* Once vma denies write, undo our temporary denial count */
- if (vm_flags & VM_DENYWRITE)
- allow_write_access(file);
+ if (file) {
+ if (vm_flags & VM_SHARED)
+ mapping_unmap_writable(file->f_mapping);
+ if (vm_flags & VM_DENYWRITE)
+ allow_write_access(file);
+ }
file = vma->vm_file;
out:
perf_event_mmap(vma);
@@ -1613,14 +1628,17 @@ out:
return addr;
unmap_and_free_vma:
- if (vm_flags & VM_DENYWRITE)
- allow_write_access(file);
vma->vm_file = NULL;
fput(file);
/* Undo any partial mapping done by a device driver. */
unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
charged = 0;
+ if (vm_flags & VM_SHARED)
+ mapping_unmap_writable(file->f_mapping);
+allow_write_and_free_vma:
+ if (vm_flags & VM_DENYWRITE)
+ allow_write_access(file);
free_vma:
kmem_cache_free(vm_area_cachep, vma);
unacct_error:
diff --git a/mm/swap_state.c b/mm/swap_state.c
index f24ab0d..3b78165 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -39,6 +39,7 @@ static struct backing_dev_info swap_backing_dev_info = {
struct address_space swapper_spaces[MAX_SWAPFILES] = {
[0 ... MAX_SWAPFILES - 1] = {
.page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
+ .i_mmap_writable = ATOMIC_INIT(0),
.a_ops = &swap_aops,
.backing_dev_info = &swap_backing_dev_info,
}