[f2fs-dev] [PATCH] f2fs: fix to zero post-eof page

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

fstest reports a f2fs bug:

generic/363 42s ... [failed, exit status 1]- output mismatch (see /share/git/fstests/results//generic/363.out.bad)
    --- tests/generic/363.out   2025-01-12 21:57:40.271440542 +0800
    +++ /share/git/fstests/results//generic/363.out.bad 2025-05-19 19:55:58.000000000 +0800
    @@ -1,2 +1,78 @@
     QA output created by 363
     fsx -q -S 0 -e 1 -N 100000
    +READ BAD DATA: offset = 0xd6fb, size = 0xf044, fname = /mnt/f2fs/junk
    +OFFSET      GOOD    BAD     RANGE
    +0x1540d     0x0000  0x2a25  0x0
    +operation# (mod 256) for the bad data may be 37
    +0x1540e     0x0000  0x2527  0x1
    ...
    (Run 'diff -u /share/git/fstests/tests/generic/363.out /share/git/fstests/results//generic/363.out.bad'  to see the entire diff)
Ran: generic/363
Failures: generic/363
Failed 1 of 1 tests

The root cause is user can update post-eof page via mmap, however, f2fs missed
to zero post-eof page in below operations, so, once it expands i_size, then it
will include dummy data locates previous post-eof page, so during below
operations, we need to zero post-eof page.

Operations which can include dummy data after previous i_size after expanding
i_size:
- write
- mapwrite
- truncate
- fallocate
 * preallocate
 * zero_range
 * insert_range
 * collapse_range
- clone_range (doesn’t support in f2fs)
- copy_range (doesn’t support in f2fs)

Cc: stable@kernel.org
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/file.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 6bd3de64f2a8..c7c66e591ebc 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -35,6 +35,17 @@
 #include <trace/events/f2fs.h>
 #include <uapi/linux/f2fs.h>
 
+static void f2fs_zero_post_eof_page(struct inode *inode, loff_t new_size)
+{
+	loff_t old_size = i_size_read(inode);
+
+	if (old_size > new_size)
+		return;
+
+	/* zero or drop pages only in range of [old_size, new_size] */
+	truncate_pagecache(inode, old_size);
+}
+
 static vm_fault_t f2fs_filemap_fault(struct vm_fault *vmf)
 {
 	struct inode *inode = file_inode(vmf->vma->vm_file);
@@ -105,6 +116,9 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 
 	file_update_time(vmf->vma->vm_file);
 	filemap_invalidate_lock_shared(inode->i_mapping);
+
+	f2fs_zero_post_eof_page(inode, (folio->index + 1) << PAGE_SHIFT);
+
 	folio_lock(folio);
 	if (unlikely(folio->mapping != inode->i_mapping ||
 			folio_pos(folio) > i_size_read(inode) ||
@@ -1109,6 +1123,8 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 		f2fs_down_write(&fi->i_gc_rwsem[WRITE]);
 		filemap_invalidate_lock(inode->i_mapping);
 
+		if (attr->ia_size > old_size)
+			f2fs_zero_post_eof_page(inode, old_size);
 		truncate_setsize(inode, attr->ia_size);
 
 		if (attr->ia_size <= old_size)
@@ -1227,6 +1243,8 @@ static int f2fs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
 	if (ret)
 		return ret;
 
+	f2fs_zero_post_eof_page(inode, offset + len);
+
 	pg_start = ((unsigned long long) offset) >> PAGE_SHIFT;
 	pg_end = ((unsigned long long) offset + len) >> PAGE_SHIFT;
 
@@ -1542,6 +1560,8 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
 	if (ret)
 		return ret;
 
+	f2fs_zero_post_eof_page(inode, offset + len);
+
 	ret = f2fs_do_collapse(inode, offset, len);
 	if (ret)
 		return ret;
@@ -1631,6 +1651,8 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len,
 	if (ret)
 		return ret;
 
+	f2fs_zero_post_eof_page(inode, offset + len);
+
 	pg_start = ((unsigned long long) offset) >> PAGE_SHIFT;
 	pg_end = ((unsigned long long) offset + len) >> PAGE_SHIFT;
 
@@ -1754,6 +1776,8 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
 	if (ret)
 		return ret;
 
+	f2fs_zero_post_eof_page(inode, offset + len);
+
 	pg_start = offset >> PAGE_SHIFT;
 	pg_end = (offset + len) >> PAGE_SHIFT;
 	delta = pg_end - pg_start;
@@ -1819,6 +1843,8 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
 	if (err)
 		return err;
 
+	f2fs_zero_post_eof_page(inode, offset + len);
+
 	f2fs_balance_fs(sbi, true);
 
 	pg_start = ((unsigned long long)offset) >> PAGE_SHIFT;
@@ -4860,6 +4886,8 @@ static ssize_t f2fs_write_checks(struct kiocb *iocb, struct iov_iter *from)
 	err = file_modified(file);
 	if (err)
 		return err;
+
+	f2fs_zero_post_eof_page(inode, iocb->ki_pos + iov_iter_count(from));
 	return count;
 }
 
-- 
2.49.0



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