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

["Namjae Jeon" <namjae.jeon@samsung.com>]

> 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directory is no longer updated.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 for your test!
> 
> 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?
Well, I am not sure that they will respond to your report well. If you can
reproduce same issue even when plugging your exfat into windows, I think
that it is worth reporting to them.

> >---
> > 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
> >