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Subject[PATCH] tmpfs 2/9 shmem_getpage beyond eof
The last set of tmpfs patches left shmem_getpage with an inadequate
next_index test to guard against races with truncation. Now remove
that check and settle the issue with checks against i_size within
shmem_swp_alloc, which needs to know whether reading or writing.

--- tmpfs1/mm/shmem.c Thu Oct 17 22:00:49 2002
+++ tmpfs2/mm/shmem.c Thu Oct 17 22:00:59 2002
@@ -51,6 +51,12 @@
/* Keep swapped page count in private field of indirect struct page */
#define nr_swapped private

+/* Flag end-of-file treatment to shmem_getpage and shmem_swp_alloc */
+enum sgp_type {
+ SGP_READ, /* don't exceed i_size */
+ SGP_WRITE, /* may exceed i_size */
+};
+
static inline struct page *shmem_dir_alloc(unsigned int gfp_mask)
{
/*
@@ -200,8 +206,6 @@
struct page **dir;
struct page *subdir;

- if (index >= info->next_index)
- return NULL;
if (index < SHMEM_NR_DIRECT)
return info->i_direct+index;
if (!info->i_indirect) {
@@ -274,20 +278,20 @@
*
* @info: info structure for the inode
* @index: index of the page to find
+ * @sgp: check and recheck i_size?
*/
-static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long index)
+static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long index, enum sgp_type sgp)
{
struct inode *inode = &info->vfs_inode;
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
struct page *page = NULL;
swp_entry_t *entry;

- while (!(entry = shmem_swp_entry(info, index, &page))) {
- if (index >= info->next_index) {
- entry = ERR_PTR(-EFAULT);
- break;
- }
+ if (sgp != SGP_WRITE &&
+ ((loff_t) index << PAGE_CACHE_SHIFT) >= inode->i_size)
+ return ERR_PTR(-EINVAL);

+ while (!(entry = shmem_swp_entry(info, index, &page))) {
/*
* Test free_blocks against 1 not 0, since we have 1 data
* page (and perhaps indirect index pages) yet to allocate:
@@ -314,12 +318,21 @@
shmem_free_block(inode);
return ERR_PTR(-ENOMEM);
}
+ if (sgp != SGP_WRITE &&
+ ((loff_t) index << PAGE_CACHE_SHIFT) >= inode->i_size) {
+ entry = ERR_PTR(-EINVAL);
+ break;
+ }
+ if (info->next_index <= index)
+ info->next_index = index + 1;
}
if (page) {
/* another task gave its page, or truncated the file */
shmem_free_block(inode);
shmem_dir_free(page);
}
+ if (info->next_index <= index && !IS_ERR(entry))
+ info->next_index = index + 1;
return entry;
}

@@ -672,6 +685,7 @@

spin_lock(&info->lock);
shmem_recalc_inode(inode);
+ BUG_ON(index >= info->next_index);
entry = shmem_swp_entry(info, index, NULL);
BUG_ON(!entry);
BUG_ON(entry->val);
@@ -710,7 +724,7 @@
* vm. If we swap it in we mark it dirty since we also free the swap
* entry since a page cannot live in both the swap and page cache
*/
-static int shmem_getpage(struct inode *inode, unsigned long idx, struct page **pagep)
+static int shmem_getpage(struct inode *inode, unsigned long idx, struct page **pagep, enum sgp_type sgp)
{
struct address_space *mapping = inode->i_mapping;
struct shmem_inode_info *info = SHMEM_I(inode);
@@ -722,18 +736,6 @@

if (idx >= SHMEM_MAX_INDEX)
return -EFBIG;
-
- /*
- * When writing, i_sem is held against truncation and other
- * writing, so next_index will remain as set here; but when
- * reading, idx must always be checked against next_index
- * after sleeping, lest truncation occurred meanwhile.
- */
- spin_lock(&info->lock);
- if (info->next_index <= idx)
- info->next_index = idx + 1;
- spin_unlock(&info->lock);
-
repeat:
page = find_lock_page(mapping, idx);
if (page) {
@@ -744,7 +746,7 @@

spin_lock(&info->lock);
shmem_recalc_inode(inode);
- entry = shmem_swp_alloc(info, idx);
+ entry = shmem_swp_alloc(info, idx, sgp);
if (IS_ERR(entry)) {
spin_unlock(&info->lock);
return PTR_ERR(entry);
@@ -761,7 +763,7 @@
page = read_swap_cache_async(swap);
if (!page) {
spin_lock(&info->lock);
- entry = shmem_swp_alloc(info, idx);
+ entry = shmem_swp_alloc(info, idx, sgp);
if (IS_ERR(entry))
error = PTR_ERR(entry);
else {
@@ -830,7 +832,7 @@
}

spin_lock(&info->lock);
- entry = shmem_swp_alloc(info, idx);
+ entry = shmem_swp_alloc(info, idx, sgp);
if (IS_ERR(entry))
error = PTR_ERR(entry);
else {
@@ -881,7 +883,7 @@
}
spin_unlock(&info->lock);
if (swap.val) {
- (void) shmem_getpage(inode, idx, &page);
+ (void) shmem_getpage(inode, idx, &page, SGP_READ);
}
return page;
}
@@ -897,10 +899,7 @@
idx += vma->vm_pgoff;
idx >>= PAGE_CACHE_SHIFT - PAGE_SHIFT;

- if (((loff_t) idx << PAGE_CACHE_SHIFT) >= inode->i_size)
- return NOPAGE_SIGBUS;
-
- error = shmem_getpage(inode, idx, &page);
+ error = shmem_getpage(inode, idx, &page, SGP_READ);
if (error)
return (error == -ENOMEM)? NOPAGE_OOM: NOPAGE_SIGBUS;

@@ -1105,7 +1104,7 @@
* what would it guard against? - so no deadlock here.
*/

- status = shmem_getpage(inode, index, &page);
+ status = shmem_getpage(inode, index, &page, SGP_WRITE);
if (status)
break;

@@ -1170,9 +1169,9 @@
break;
}

- desc->error = shmem_getpage(inode, index, &page);
+ desc->error = shmem_getpage(inode, index, &page, SGP_READ);
if (desc->error) {
- if (desc->error == -EFAULT)
+ if (desc->error == -EINVAL)
desc->error = 0;
break;
}
@@ -1419,7 +1418,7 @@
iput(inode);
return -ENOMEM;
}
- error = shmem_getpage(inode, 0, &page);
+ error = shmem_getpage(inode, 0, &page, SGP_WRITE);
if (error) {
vm_unacct_memory(VM_ACCT(1));
iput(inode);
@@ -1455,7 +1454,7 @@
static int shmem_readlink(struct dentry *dentry, char *buffer, int buflen)
{
struct page *page;
- int res = shmem_getpage(dentry->d_inode, 0, &page);
+ int res = shmem_getpage(dentry->d_inode, 0, &page, SGP_READ);
if (res)
return res;
res = vfs_readlink(dentry, buffer, buflen, kmap(page));
@@ -1467,7 +1466,7 @@
static int shmem_follow_link(struct dentry *dentry, struct nameidata *nd)
{
struct page *page;
- int res = shmem_getpage(dentry->d_inode, 0, &page);
+ int res = shmem_getpage(dentry->d_inode, 0, &page, SGP_READ);
if (res)
return res;
res = vfs_follow_link(nd, kmap(page));
-
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