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authorJan Kara <jack@suse.cz>2014-10-01 21:49:18 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-14 08:47:54 -0800
commit6cbdf1151168e44f93866f6af751442b937f8989 (patch)
tree5306e33c4c5fbee9e5d6694e95a31f9b1b7f337c /include/linux
parent6f1aec53eded9399e6b44cab8c9aa36c65a8f402 (diff)
vfs: fix data corruption when blocksize < pagesize for mmaped data
commit 90a8020278c1598fafd071736a0846b38510309c upstream. ->page_mkwrite() is used by filesystems to allocate blocks under a page which is becoming writeably mmapped in some process' address space. This allows a filesystem to return a page fault if there is not enough space available, user exceeds quota or similar problem happens, rather than silently discarding data later when writepage is called. However VFS fails to call ->page_mkwrite() in all the cases where filesystems need it when blocksize < pagesize. For example when blocksize = 1024, pagesize = 4096 the following is problematic: ftruncate(fd, 0); pwrite(fd, buf, 1024, 0); map = mmap(NULL, 1024, PROT_WRITE, MAP_SHARED, fd, 0); map[0] = 'a'; ----> page_mkwrite() for index 0 is called ftruncate(fd, 10000); /* or even pwrite(fd, buf, 1, 10000) */ mremap(map, 1024, 10000, 0); map[4095] = 'a'; ----> no page_mkwrite() called At the moment ->page_mkwrite() is called, filesystem can allocate only one block for the page because i_size == 1024. Otherwise it would create blocks beyond i_size which is generally undesirable. But later at ->writepage() time, we also need to store data at offset 4095 but we don't have block allocated for it. This patch introduces a helper function filesystems can use to have ->page_mkwrite() called at all the necessary moments. Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/mm.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a9a48309f045..7da14357aa76 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1004,6 +1004,7 @@ static inline void unmap_shared_mapping_range(struct address_space *mapping,
extern void truncate_pagecache(struct inode *inode, loff_t old, loff_t new);
extern void truncate_setsize(struct inode *inode, loff_t newsize);
+void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to);
void truncate_pagecache_range(struct inode *inode, loff_t offset, loff_t end);
int truncate_inode_page(struct address_space *mapping, struct page *page);
int generic_error_remove_page(struct address_space *mapping, struct page *page);