linux-kernel - Re: [syzbot] WARNING in iomap

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Message-ID: <20220818110031.89467-1-code@siddh.me>
Date:   Thu, 18 Aug 2022 16:30:31 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     david@...morbit.com
Cc:     djwong@...nel.org, fgheet255t@...il.com, hch@...radead.org,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        riteshh@...ux.ibm.com,
        syzbot+a8e049cd3abd342936b6@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] WARNING in iomap_iter

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.git 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 {
 	__u64		   lo_device;			/* ioctl r/o */
 	__u64		   lo_inode;			/* ioctl r/o */
 	__u64		   lo_rdevice;			/* ioctl r/o */
-	__u64		   lo_offset;
-	__u64		   lo_sizelimit;/* bytes, 0 == max available */
-	__u32		   lo_number;			/* ioctl r/o */
-	__u32		   lo_encrypt_type;		/* obsolete, ignored */
-	__u32		   lo_encrypt_key_size;		/* ioctl w/o */
-	__u32		   lo_flags;
+	__s64		   lo_offset;
+	__s64		   lo_sizelimit;	/* bytes, 0 == max available */
+	__s32		   lo_number;			/* ioctl r/o */
+	__s32		   lo_encrypt_type;		/* obsolete, ignored */
+	__s32		   lo_encrypt_key_size;		/* ioctl w/o */
+	__s32		   lo_flags;
 	__u8		   lo_file_name[LO_NAME_SIZE];
 	__u8		   lo_crypt_name[LO_NAME_SIZE];
 	__u8		   lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
-- 
2.35.1