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From:   Siddh Raman Pant <code@siddh.me>
To:     david@fromorbit.com
Cc:     djwong@kernel.org, fgheet255t@gmail.com, hch@infradead.org,
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Message-ID: <20220818110031.89467-1-code@siddh.me>
Subject: Re: [syzbot] WARNING in iomap_iter
Date:   Thu, 18 Aug 2022 16:30:31 +0530
In-Reply-To: <20220214025849.GP59729@dread.disaster.area>
References: <20220214025849.GP59729@dread.disaster.area>
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This is probably due to mismatch in types between userspace API struct
and the kernel's internal struct, which leads to offset being overflowed
after getting converted from __u64 (unsigned long long) to loff_t (signed
long long), resulting in ridiculously negative offset value.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.gi=
t master

---
 include/uapi/linux/loop.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h
index 6f63527dd2ed..33c07c467da4 100644
--- a/include/uapi/linux/loop.h
+++ b/include/uapi/linux/loop.h
@@ -53,12 +53,12 @@ struct loop_info64 {
 =09__u64=09=09   lo_device;=09=09=09/* ioctl r/o */
 =09__u64=09=09   lo_inode;=09=09=09/* ioctl r/o */
 =09__u64=09=09   lo_rdevice;=09=09=09/* ioctl r/o */
-=09__u64=09=09   lo_offset;
-=09__u64=09=09   lo_sizelimit;/* bytes, 0 =3D=3D max available */
-=09__u32=09=09   lo_number;=09=09=09/* ioctl r/o */
-=09__u32=09=09   lo_encrypt_type;=09=09/* obsolete, ignored */
-=09__u32=09=09   lo_encrypt_key_size;=09=09/* ioctl w/o */
-=09__u32=09=09   lo_flags;
+=09__s64=09=09   lo_offset;
+=09__s64=09=09   lo_sizelimit;=09/* bytes, 0 =3D=3D max available */
+=09__s32=09=09   lo_number;=09=09=09/* ioctl r/o */
+=09__s32=09=09   lo_encrypt_type;=09=09/* obsolete, ignored */
+=09__s32=09=09   lo_encrypt_key_size;=09=09/* ioctl w/o */
+=09__s32=09=09   lo_flags;
 =09__u8=09=09   lo_file_name[LO_NAME_SIZE];
 =09__u8=09=09   lo_crypt_name[LO_NAME_SIZE];
 =09__u8=09=09   lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
--=20
2.35.1