From: Siddh Raman Pant code@siddh.me
[ Upstream commit 6acd87d50998ef0afafc441613aeaf5a8f5c9eff ]
Effective offset to add to length was being incorrectly calculated, which resulted in iomap->length being set to 0, triggering a WARN_ON in iomap_iter_done().
Fix that, and describe it in comments.
This was reported as a crash by syzbot under an issue about a warning encountered in iomap_iter_done(), but unrelated to erofs.
C reproducer: https://syzkaller.appspot.com/text?tag=ReproC&x=1037a6b2880000 Kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=e2021a61197ebe02 Dashboard link: https://syzkaller.appspot.com/bug?extid=a8e049cd3abd342936b6
Reported-by: syzbot+a8e049cd3abd342936b6@syzkaller.appspotmail.com Suggested-by: Gao Xiang hsiangkao@linux.alibaba.com Signed-off-by: Siddh Raman Pant code@siddh.me Reviewed-by: Gao Xiang hsiangkao@linux.alibaba.com Reviewed-by: Chao Yu chao@kernel.org Link: https://lore.kernel.org/r/20221209102151.311049-1-code@siddh.me Signed-off-by: Gao Xiang hsiangkao@linux.alibaba.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/erofs/zmap.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c index e6d5d7a18fb0..39cc014dba40 100644 --- a/fs/erofs/zmap.c +++ b/fs/erofs/zmap.c @@ -793,12 +793,16 @@ static int z_erofs_iomap_begin_report(struct inode *inode, loff_t offset, iomap->type = IOMAP_HOLE; iomap->addr = IOMAP_NULL_ADDR; /* - * No strict rule how to describe extents for post EOF, yet - * we need do like below. Otherwise, iomap itself will get + * No strict rule on how to describe extents for post EOF, yet + * we need to do like below. Otherwise, iomap itself will get * into an endless loop on post EOF. + * + * Calculate the effective offset by subtracting extent start + * (map.m_la) from the requested offset, and add it to length. + * (NB: offset >= map.m_la always) */ if (iomap->offset >= inode->i_size) - iomap->length = length + map.m_la - offset; + iomap->length = length + offset - map.m_la; } iomap->flags = 0; return 0;