Commit 14da9200 authored by Jan Kara's avatar Jan Kara Committed by Al Viro

fs: Protect write paths by sb_start_write - sb_end_write

There are several entry points which dirty pages in a filesystem.  mmap
(handled by block_page_mkwrite()), buffered write (handled by
__generic_file_aio_write()), splice write (generic_file_splice_write),
truncate, and fallocate (these can dirty last partial page - handled inside
each filesystem separately). Protect these places with sb_start_write() and
sb_end_write().

->page_mkwrite() calls are particularly complex since they are called with
mmap_sem held and thus we cannot use standard sb_start_write() due to lock
ordering constraints. We solve the problem by using a special freeze protection
sb_start_pagefault() which ranks below mmap_sem.

BugLink: https://bugs.launchpad.net/bugs/897421Tested-by: default avatarKamal Mostafa <kamal@canonical.com>
Tested-by: default avatarPeter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: default avatarDann Frazier <dann.frazier@canonical.com>
Tested-by: default avatarMassimo Morana <massimo.morana@canonical.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 5d37e9e6
......@@ -2306,8 +2306,8 @@ EXPORT_SYMBOL(block_commit_write);
* beyond EOF, then the page is guaranteed safe against truncation until we
* unlock the page.
*
* Direct callers of this function should call vfs_check_frozen() so that page
* fault does not busyloop until the fs is thawed.
* Direct callers of this function should protect against filesystem freezing
* using sb_start_write() - sb_end_write() functions.
*/
int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
get_block_t get_block)
......@@ -2345,18 +2345,7 @@ int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
if (unlikely(ret < 0))
goto out_unlock;
/*
* Freezing in progress? We check after the page is marked dirty and
* with page lock held so if the test here fails, we are sure freezing
* code will wait during syncing until the page fault is done - at that
* point page will be dirty and unlocked so freezing code will write it
* and writeprotect it again.
*/
set_page_dirty(page);
if (inode->i_sb->s_frozen != SB_UNFROZEN) {
ret = -EAGAIN;
goto out_unlock;
}
wait_on_page_writeback(page);
return 0;
out_unlock:
......@@ -2371,12 +2360,9 @@ int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
int ret;
struct super_block *sb = vma->vm_file->f_path.dentry->d_inode->i_sb;
/*
* This check is racy but catches the common case. The check in
* __block_page_mkwrite() is reliable.
*/
vfs_check_frozen(sb, SB_FREEZE_WRITE);
sb_start_pagefault(sb);
ret = __block_page_mkwrite(vma, vmf, get_block);
sb_end_pagefault(sb);
return block_page_mkwrite_return(ret);
}
EXPORT_SYMBOL(block_page_mkwrite);
......
......@@ -164,11 +164,13 @@ static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
if (IS_APPEND(inode))
goto out_putf;
sb_start_write(inode->i_sb);
error = locks_verify_truncate(inode, file, length);
if (!error)
error = security_path_truncate(&file->f_path);
if (!error)
error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, file);
sb_end_write(inode->i_sb);
out_putf:
fput(file);
out:
......@@ -266,7 +268,10 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
if (!file->f_op->fallocate)
return -EOPNOTSUPP;
return file->f_op->fallocate(file, mode, offset, len);
sb_start_write(inode->i_sb);
ret = file->f_op->fallocate(file, mode, offset, len);
sb_end_write(inode->i_sb);
return ret;
}
SYSCALL_DEFINE(fallocate)(int fd, int mode, loff_t offset, loff_t len)
......
......@@ -996,6 +996,8 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
};
ssize_t ret;
sb_start_write(inode->i_sb);
pipe_lock(pipe);
splice_from_pipe_begin(&sd);
......@@ -1034,6 +1036,7 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
*ppos += ret;
balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
}
sb_end_write(inode->i_sb);
return ret;
}
......
......@@ -1718,6 +1718,7 @@ int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
int ret = VM_FAULT_LOCKED;
sb_start_pagefault(inode->i_sb);
file_update_time(vma->vm_file);
lock_page(page);
if (page->mapping != inode->i_mapping) {
......@@ -1725,7 +1726,14 @@ int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
ret = VM_FAULT_NOPAGE;
goto out;
}
/*
* We mark the page dirty already here so that when freeze is in
* progress, we are guaranteed that writeback during freezing will
* see the dirty page and writeprotect it again.
*/
set_page_dirty(page);
out:
sb_end_pagefault(inode->i_sb);
return ret;
}
EXPORT_SYMBOL(filemap_page_mkwrite);
......@@ -2426,8 +2434,6 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
count = ocount;
pos = *ppos;
vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
/* We can write back this queue in page reclaim */
current->backing_dev_info = mapping->backing_dev_info;
written = 0;
......@@ -2526,6 +2532,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
BUG_ON(iocb->ki_pos != pos);
sb_start_write(inode->i_sb);
mutex_lock(&inode->i_mutex);
blk_start_plug(&plug);
ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
......@@ -2539,6 +2546,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
ret = err;
}
blk_finish_plug(&plug);
sb_end_write(inode->i_sb);
return ret;
}
EXPORT_SYMBOL(generic_file_aio_write);
......
......@@ -402,6 +402,8 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
loff_t pos;
ssize_t ret;
sb_start_write(inode->i_sb);
mutex_lock(&inode->i_mutex);
if (!access_ok(VERIFY_READ, buf, len)) {
......@@ -412,8 +414,6 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
pos = *ppos;
count = len;
vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
/* We can write back this queue in page reclaim */
current->backing_dev_info = mapping->backing_dev_info;
......@@ -437,6 +437,7 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
current->backing_dev_info = NULL;
out_up:
mutex_unlock(&inode->i_mutex);
sb_end_write(inode->i_sb);
return ret;
}
EXPORT_SYMBOL_GPL(xip_file_write);
......
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