Re: [PATCH] exfat: handle wrong stream entry size in exfat_readdir()

[Chris Down <chris@chrisdown.name>]

Namjae Jeon writes:
>The compatibility issue between linux exfat and exfat of some camera
>company was reported from Florian. In their exfat, if the number of files
>exceeds any limit, the DataLength in stream entry of the directory is
>no longer updated. So some files created from camera does not show in
>linux exfat. because linux exfat doesn't allow that cpos becomes larger
>than DataLength of stream entry. This patch check DataLength in stream
>entry only if the type is ALLOC_NO_FAT_CHAIN and add the check ensure
>that dentry offset does not exceed max dentries size(256 MB) to avoid
>the circular FAT chain issue.
>
>Fixes: ca06197382bd ("exfat: add directory operations")
>Cc: stable@vger.kernel.org # v5.9
>Reported-by: Florian Cramer <flrncrmr@gmail.com>
>Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
>Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>

Tested-by: Chris Down <chris@chrisdown.name>

Thanks, I came across this while debugging why directories produced on my Fuji 
X-T4 were truncated at 2^12 dentries.

If the other report was also Fuji, maybe this is worth asking them to fix in 
firmware?

>---
> fs/exfat/dir.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
>diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
>index c4523648472a..f4e4d8d9894d 100644
>--- a/fs/exfat/dir.c
>+++ b/fs/exfat/dir.c
>@@ -63,7 +63,7 @@ static void exfat_get_uniname_from_ext_entry(struct super_block *sb,
> static int exfat_readdir(struct inode *inode, loff_t *cpos, struct exfat_dir_entry *dir_entry)
> {
> 	int i, dentries_per_clu, dentries_per_clu_bits = 0, num_ext;
>-	unsigned int type, clu_offset;
>+	unsigned int type, clu_offset, max_dentries;
> 	sector_t sector;
> 	struct exfat_chain dir, clu;
> 	struct exfat_uni_name uni_name;
>@@ -86,6 +86,8 @@ static int exfat_readdir(struct inode *inode, loff_t *cpos, struct exfat_dir_ent
>
> 	dentries_per_clu = sbi->dentries_per_clu;
> 	dentries_per_clu_bits = ilog2(dentries_per_clu);
>+	max_dentries = (unsigned int)min_t(u64, MAX_EXFAT_DENTRIES,
>+					   (u64)sbi->num_clusters << dentries_per_clu_bits);
>
> 	clu_offset = dentry >> dentries_per_clu_bits;
> 	exfat_chain_dup(&clu, &dir);
>@@ -109,7 +111,7 @@ static int exfat_readdir(struct inode *inode, loff_t *cpos, struct exfat_dir_ent
> 		}
> 	}
>
>-	while (clu.dir != EXFAT_EOF_CLUSTER) {
>+	while (clu.dir != EXFAT_EOF_CLUSTER && dentry < max_dentries) {
> 		i = dentry & (dentries_per_clu - 1);
>
> 		for ( ; i < dentries_per_clu; i++, dentry++) {
>@@ -245,7 +247,7 @@ static int exfat_iterate(struct file *filp, struct dir_context *ctx)
> 	if (err)
> 		goto unlock;
> get_new:
>-	if (cpos >= i_size_read(inode))
>+	if (ei->flags == ALLOC_NO_FAT_CHAIN && cpos >= i_size_read(inode))
> 		goto end_of_dir;
>
> 	err = exfat_readdir(inode, &cpos, &de);
>-- 
>2.17.1
>