[f2fs-dev] [PATCH v2] f2fs: Restrict max filesize for 16K f2fs

[f2fs-dev] [PATCH v2] f2fs: Restrict max filesize for 16K f2fs

[Daniel Rosenberg via Linux-f2fs-devel]

Blocks are tracked by u32, so the max permitted filesize is
U32_MAX * BLOCK_SIZE. Additionally, in order to support crypto data unit
sizes of 4K with a 16K block size with IV_INO_LBLK_{32,63}, we must
further restrict max filesize to U32_MAX * 4096. This does not affect 4K
blocksize f2fs as the natural limit for files are well below that.

Fixes: d7e9a9037de2 ("f2fs: Support Block Size == Page Size")
Signed-off-by: Daniel Rosenberg <drosen@google.com>
---
 fs/f2fs/super.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 033af907c3b1..18a2189a0dc4 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -3364,6 +3364,18 @@ loff_t max_file_blocks(struct inode *inode)
 	leaf_count *= NIDS_PER_BLOCK;
 	result += leaf_count;
 
+	/*
+	 * For compatibility with FSCRYPT_POLICY_IV_INO_LBLK_{64,32} with a
+	 * 4K crypto data unit, we must restrict the max filesize to what can
+	 * fit within U32_MAX data units.
+	 *
+	 * Since the blocksize must currently be equal to the page size,
+	 * we can use a constant for that. Note if this is not the case
+	 * in the future that inode is NULL while setting up the superblock.
+	 */
+
+	result = min(result, ((loff_t) U32_MAX * 4096) >> F2FS_BLKSIZE_BITS);
+
 	return result;
 }
 

base-commit: d346fa09abff46988de9267b67b6900d9913d5a2
-- 
2.43.0.rc2.451.g8631bc7472-goog



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Re: [f2fs-dev] [PATCH v2] f2fs: Restrict max filesize for 16K f2fs

[Eric Biggers]

On Mon, Dec 04, 2023 at 03:46:15PM -0800, Daniel Rosenberg via Linux-f2fs-devel wrote:
> Blocks are tracked by u32, so the max permitted filesize is
> U32_MAX * BLOCK_SIZE. Additionally, in order to support crypto data unit
> sizes of 4K with a 16K block size with IV_INO_LBLK_{32,63}, we must

{32,63} should be {32,64}

> +	/*
> +	 * For compatibility with FSCRYPT_POLICY_IV_INO_LBLK_{64,32} with a
> +	 * 4K crypto data unit, we must restrict the max filesize to what can
> +	 * fit within U32_MAX data units.

FSCRYPT_POLICY_IV_INO_LBLK_{64,32} should be
FSCRYPT_POLICY_FLAG_IV_INO_LBLK_{64,32}

> +	 *
> +	 * Since the blocksize must currently be equal to the page size,
> +	 * we can use a constant for that. Note if this is not the case
> +	 * in the future that inode is NULL while setting up the superblock.

I'm not sure what the last sentence is trying to say.

> +	 */
> +
> +	result = min(result, ((loff_t) U32_MAX * 4096) >> F2FS_BLKSIZE_BITS);

Is it intentional that this is off by 1?  If indices can be up to U32_MAX, then
the maximum size is U32_MAX + 1.  It's not a bad idea to go with the lower size,
so that max_index + 1 does not overflow.  But that's not what the explanation
says, so this seems to be accidental.

- Eric


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