[PATCH] erofs: avoid reading more for fragment maps

[Chao Yu]

On 9/16/25 16:48, Gao Xiang wrote:
> Since all real encoded extents (directly handled by the decompression
> subsystem) have a sane, limited maximum decoded length
> (Z_EROFS_PCLUSTER_MAX_DSIZE), and the read‑more policy is only applied
> if needed.
> 
> However, it makes no sense to read more for non‑encoded maps, such as
> fragment extents, since such extents can be huge (up to i_size) and
> there is no benefit to reading more at this layer.
> 
> For normal images, it does not really matter, but for crafted images
> generated by syzbot, excessively large fragment extents can cause
> read‑more to run for an overly long time.
> 
> Reported-by: syzbot+1a9af3ef3c84c5e14dcc at syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/r/68c8583d.050a0220.2ff435.03a3.GAE@google.com
> Fixes: b44686c8391b ("erofs: fix large fragment handling")
> Fixes: b15b2e307c3a ("erofs: support on-disk compressed fragments data")
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>

Reviewed-by: Chao Yu <chao at kernel.org>

Thanks,