[PATCH v3 1/3] f2fs: fix to avoid overflow while left shift operation

[PATCH v3 1/3] f2fs: fix to avoid overflow while left shift operation

[Chao Yu]

Should cast type of folio->index from pgoff_t to loff_t to avoid overflow
while left shift operation.

Fixes: 3265d3db1f16 ("f2fs: support partial truncation on compressed inode")
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/compress.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 5c1f47e45dab..6cd8902849cf 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1245,7 +1245,7 @@ int f2fs_truncate_partial_cluster(struct inode *inode, u64 from, bool lock)
 
 		for (i = cluster_size - 1; i >= 0; i--) {
 			struct folio *folio = page_folio(rpages[i]);
-			loff_t start = folio->index << PAGE_SHIFT;
+			loff_t start = (loff_t)folio->index << PAGE_SHIFT;
 
 			if (from <= start) {
 				folio_zero_segment(folio, 0, folio_size(folio));
-- 
2.49.0

[PATCH v3 2/3] f2fs: fix to zero data after EOF for compressed file correctly

[Chao Yu]

generic/091 may fail, then it bisects to the bad commit ba8dac350faf
("f2fs: fix to zero post-eof page").

What will cause generic/091 to fail is something like below Testcase #1:
1. write 16k as compressed blocks
2. truncate to 12k
3. truncate to 20k
4. verify data in range of [12k, 16k], however data is not zero as
expected

Script of Testcase #1
mkfs.f2fs -f -O extra_attr,compression /dev/vdb
mount -t f2fs -o compress_extension=* /dev/vdb /mnt/f2fs
dd if=/dev/zero of=/mnt/f2fs/file bs=12k count=1
dd if=/dev/random of=/mnt/f2fs/file bs=4k count=1 seek=3 conv=notrunc
sync
truncate -s $((12*1024)) /mnt/f2fs/file
truncate -s $((20*1024)) /mnt/f2fs/file
dd if=/mnt/f2fs/file of=/mnt/f2fs/data bs=4k count=1 skip=3
od /mnt/f2fs/data
umount /mnt/f2fs

Analisys:
in step 2), we will redirty all data pages from #0 to #3 in compressed
cluster, and zero page #3,
in step 3), f2fs_setattr() will call f2fs_zero_post_eof_page() to drop
all page cache post eof, includeing dirtied page #3,
in step 4) when we read data from page #3, it will decompressed cluster
and extra random data to page #3, finally, we hit the non-zeroed data
post eof.

However, the commit ba8dac350faf ("f2fs: fix to zero post-eof page") just
let the issue be reproduced easily, w/o the commit, it can reproduce this
bug w/ below Testcase #2:
1. write 16k as compressed blocks
2. truncate to 8k
3. truncate to 12k
4. truncate to 20k
5. verify data in range of [12k, 16k], however data is not zero as
expected

Script of Testcase #2
mkfs.f2fs -f -O extra_attr,compression /dev/vdb
mount -t f2fs -o compress_extension=* /dev/vdb /mnt/f2fs
dd if=/dev/zero of=/mnt/f2fs/file bs=12k count=1
dd if=/dev/random of=/mnt/f2fs/file bs=4k count=1 seek=3 conv=notrunc
sync
truncate -s $((8*1024)) /mnt/f2fs/file
truncate -s $((12*1024)) /mnt/f2fs/file
truncate -s $((20*1024)) /mnt/f2fs/file
echo 3 > /proc/sys/vm/drop_caches
dd if=/mnt/f2fs/file of=/mnt/f2fs/data bs=4k count=1 skip=3
od /mnt/f2fs/data
umount /mnt/f2fs

Anlysis:
in step 2), we will redirty all data pages from #0 to #3 in compressed
cluster, and zero page #2 and #3,
in step 3), we will truncate page #3 in page cache,
in step 4), expand file size,
in step 5), hit random data post eof w/ the same reason in Testcase #1.

Root Cause:
In f2fs_truncate_partial_cluster(), after we truncate partial data block
on compressed cluster, all pages in cluster including the one post eof
will be dirtied, after another tuncation, dirty page post eof will be
dropped, however on-disk compressed cluster is still valid, it includes
invalid data post eof, result in exposing previous data post eof while
reading.

Fix:
In f2fs_truncate_partial_cluster(), let change as below to fix:
- call filemap_write_and_wait_range() to flush dirty page
- call truncate_pagecache() to drop pages or zero partial page post eof
- call f2fs_do_truncate_blocks() to truncate non-compress cluster to
  last vali block

Fixes: 3265d3db1f16 ("f2fs: support partial truncation on compressed inode")
Reported-by: Jan Prusakowski <jprusakowski@google.com>
Signed-off-by: Chao Yu <chao@kernel.org>
---
v3:
- reorder patch 2 and patch 3
 fs/f2fs/compress.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 6cd8902849cf..72bc05b913af 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1246,19 +1246,28 @@ int f2fs_truncate_partial_cluster(struct inode *inode, u64 from, bool lock)
 		for (i = cluster_size - 1; i >= 0; i--) {
 			struct folio *folio = page_folio(rpages[i]);
 			loff_t start = (loff_t)folio->index << PAGE_SHIFT;
+			loff_t offset = from > start ? from - start : 0;
 
-			if (from <= start) {
-				folio_zero_segment(folio, 0, folio_size(folio));
-			} else {
-				folio_zero_segment(folio, from - start,
-						folio_size(folio));
+			folio_zero_segment(folio, offset, folio_size(folio));
+
+			if (from >= start)
 				break;
-			}
 		}
 
 		f2fs_compress_write_end(inode, fsdata, start_idx, true);
+
+		err = filemap_write_and_wait_range(inode->i_mapping,
+				round_down(from, cluster_size << PAGE_SHIFT),
+				LLONG_MAX);
+		if (err)
+			return err;
+
+		truncate_pagecache(inode, from);
+
+		err = f2fs_do_truncate_blocks(inode,
+				round_up(from, PAGE_SIZE), lock);
 	}
-	return 0;
+	return err;
 }
 
 static int f2fs_write_compressed_pages(struct compress_ctx *cc,
-- 
2.49.0

[PATCH v3 3/3] f2fs: clean up f2fs_truncate_partial_cluster()

[Chao Yu]

Clean up codes as below:
- avoid unnecessary "err > 0" check condition
- use "1 << log_cluster_size" instead of F2FS_I(inode)->i_cluster_size

No logic changes.

Signed-off-by: Chao Yu <chao@kernel.org>
---
v3:
- reorder patch 2 and patch 3
 fs/f2fs/compress.c | 42 +++++++++++++++++++-----------------------
 1 file changed, 19 insertions(+), 23 deletions(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 72bc05b913af..6ad8d3bc6df7 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1215,9 +1215,11 @@ int f2fs_truncate_partial_cluster(struct inode *inode, u64 from, bool lock)
 {
 	void *fsdata = NULL;
 	struct page *pagep;
+	struct page **rpages;
 	int log_cluster_size = F2FS_I(inode)->i_log_cluster_size;
 	pgoff_t start_idx = from >> (PAGE_SHIFT + log_cluster_size) <<
 							log_cluster_size;
+	int i;
 	int err;
 
 	err = f2fs_is_compressed_cluster(inode, start_idx);
@@ -1238,36 +1240,30 @@ int f2fs_truncate_partial_cluster(struct inode *inode, u64 from, bool lock)
 	if (err <= 0)
 		return err;
 
-	if (err > 0) {
-		struct page **rpages = fsdata;
-		int cluster_size = F2FS_I(inode)->i_cluster_size;
-		int i;
+	rpages = fsdata;
 
-		for (i = cluster_size - 1; i >= 0; i--) {
-			struct folio *folio = page_folio(rpages[i]);
-			loff_t start = (loff_t)folio->index << PAGE_SHIFT;
-			loff_t offset = from > start ? from - start : 0;
+	for (i = (1 << log_cluster_size) - 1; i >= 0; i--) {
+		struct folio *folio = page_folio(rpages[i]);
+		loff_t start = (loff_t)folio->index << PAGE_SHIFT;
+		loff_t offset = from > start ? from - start : 0;
 
-			folio_zero_segment(folio, offset, folio_size(folio));
+		folio_zero_segment(folio, offset, folio_size(folio));
 
-			if (from >= start)
-				break;
-		}
+		if (from >= start)
+			break;
+	}
 
-		f2fs_compress_write_end(inode, fsdata, start_idx, true);
+	f2fs_compress_write_end(inode, fsdata, start_idx, true);
 
-		err = filemap_write_and_wait_range(inode->i_mapping,
-				round_down(from, cluster_size << PAGE_SHIFT),
-				LLONG_MAX);
-		if (err)
-			return err;
+	err = filemap_write_and_wait_range(inode->i_mapping,
+			round_down(from, 1 << log_cluster_size << PAGE_SHIFT),
+			LLONG_MAX);
+	if (err)
+		return err;
 
-		truncate_pagecache(inode, from);
+	truncate_pagecache(inode, from);
 
-		err = f2fs_do_truncate_blocks(inode,
-				round_up(from, PAGE_SIZE), lock);
-	}
-	return err;
+	return f2fs_do_truncate_blocks(inode, round_up(from, PAGE_SIZE), lock);
 }
 
 static int f2fs_write_compressed_pages(struct compress_ctx *cc,
-- 
2.49.0

Re: [f2fs-dev] [PATCH v3 1/3] f2fs: fix to avoid overflow while left shift operation

[patchwork-bot+f2fs]

Hello:

This series was applied to jaegeuk/f2fs.git (dev)
by Jaegeuk Kim <jaegeuk@kernel.org>:

On Tue,  5 Aug 2025 14:29:10 +0800 you wrote:
> Should cast type of folio->index from pgoff_t to loff_t to avoid overflow
> while left shift operation.
> 
> Fixes: 3265d3db1f16 ("f2fs: support partial truncation on compressed inode")
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
>  fs/f2fs/compress.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Here is the summary with links:
  - [f2fs-dev,v3,1/3] f2fs: fix to avoid overflow while left shift operation
    https://git.kernel.org/jaegeuk/f2fs/c/0fe1c6bec54e
  - [f2fs-dev,v3,2/3] f2fs: fix to zero data after EOF for compressed file correctly
    https://git.kernel.org/jaegeuk/f2fs/c/0b2cd5092139
  - [f2fs-dev,v3,3/3] f2fs: clean up f2fs_truncate_partial_cluster()
    https://git.kernel.org/jaegeuk/f2fs/c/cbba5038ee29

You are awesome, thank you!
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