linux-kernel - Re: [PATCH v2] ext2: Handle fiemap on empty files to prevent EINVAL

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Message-ID: <mxios5pbq3vq5267on4vnt5siozd4nap5w7wemsd2vlxoooexd@ia2ezhdu7ujq>
Date: Fri, 13 Jun 2025 11:42:17 +0200
From: Jan Kara <jack@...e.cz>
To: Wei Gao <wegao@...e.com>
Cc: Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org, 
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2] ext2: Handle fiemap on empty files to prevent EINVAL

On Fri 13-06-25 11:18:38, Wei Gao wrote:
> Previously, ext2_fiemap would unconditionally apply "len = min_t(u64, len,
> i_size_read(inode));", When inode->i_size was 0 (for an empty file), this
> would reduce the requested len to 0. Passing len = 0 to iomap_fiemap could
> then result in an -EINVAL error, even for valid queries on empty files.
> 
> Link: https://github.com/linux-test-project/ltp/issues/1246
> Signed-off-by: Wei Gao <wegao@...e.com>

...

> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index 30f8201c155f..591db2b4390a 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -895,9 +895,15 @@ int ext2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>  		u64 start, u64 len)
>  {
>  	int ret;
> +	u64 i_size;
>  
>  	inode_lock(inode);
> -	len = min_t(u64, len, i_size_read(inode));
> +
> +	i_size = i_size_read(inode);
> +
> +	if (i_size > 0)
> +		len = min_t(u64, len, i_size_read(inode));


Thanks! This would actually lead to excessively slow fiemap for 0-length
files. So what I've ended up with is attached modification of your patch.

> +
>  	ret = iomap_fiemap(inode, fieinfo, start, len, &ext2_iomap_ops);
>  	inode_unlock(inode);
>  
> -- 
> 2.49.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
---

>From a099b09a3342a0b28ea330e405501b5b4d0424b4 Mon Sep 17 00:00:00 2001
From: Wei Gao <wegao@...e.com>
Date: Fri, 13 Jun 2025 11:18:38 -0400
Subject: [PATCH] ext2: Handle fiemap on empty files to prevent EINVAL

Previously, ext2_fiemap would unconditionally apply "len = min_t(u64, len,
i_size_read(inode));", When inode->i_size was 0 (for an empty file), this
would reduce the requested len to 0. Passing len = 0 to iomap_fiemap could
then result in an -EINVAL error, even for valid queries on empty files.

Link: https://github.com/linux-test-project/ltp/issues/1246
Signed-off-by: Wei Gao <wegao@...e.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Link: https://patch.msgid.link/20250613152402.3432135-1-wegao@suse.com
---
 fs/ext2/inode.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 30f8201c155f..177b1f852b63 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -895,9 +895,19 @@ int ext2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		u64 start, u64 len)
 {
 	int ret;
+	loff_t i_size;
 
 	inode_lock(inode);
-	len = min_t(u64, len, i_size_read(inode));
+	i_size = i_size_read(inode);
+	/*
+	 * iomap_fiemap() returns EINVAL for 0 length. Make sure we don't trim
+	 * length to 0 but still trim the range as much as possible since
+	 * ext2_get_blocks() iterates unmapped space block by block which is
+	 * slow.
+	 */
+	if (i_size == 0)
+		i_size = 1;
+	len = min_t(u64, len, i_size);
 	ret = iomap_fiemap(inode, fieinfo, start, len, &ext2_iomap_ops);
 	inode_unlock(inode);
 
-- 
2.43.0