[syzbot] [btrfs?] KMSAN: uninit-value in iov_iter_alignment_iovec

[syzbot] [btrfs?] KMSAN: uninit-value in iov_iter_alignment_iovec

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    614da38e2f7a Merge tag 'hid-for-linus-2024051401' of git:/..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=166b7286980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f5d2cbf33633f507
dashboard link: https://syzkaller.appspot.com/bug?extid=f2a9c06bfaa027217ebb
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=113f7f16980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11698dce980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/89eafb874b71/disk-614da38e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/356000512ad9/vmlinux-614da38e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/839c73939115/bzImage-614da38e.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/b8b22127e3de/mount_2.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f2a9c06bfaa027217ebb@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in iov_iter_alignment_iovec+0x1a8/0x470 lib/iov_iter.c:788
 iov_iter_alignment_iovec+0x1a8/0x470 lib/iov_iter.c:788
 iov_iter_alignment+0x1aa/0x290 lib/iov_iter.c:833
 check_direct_IO fs/btrfs/file.c:1452 [inline]
 check_direct_read fs/btrfs/file.c:3736 [inline]
 btrfs_direct_read fs/btrfs/file.c:3765 [inline]
 btrfs_file_read_iter+0x46f/0xc70 fs/btrfs/file.c:3826
 call_read_iter include/linux/fs.h:2114 [inline]
 aio_read+0x4b3/0x690 fs/aio.c:1611
 io_submit_one+0x2809/0x3280 fs/aio.c:2061
 __do_sys_io_submit fs/aio.c:2120 [inline]
 __se_sys_io_submit+0x275/0x700 fs/aio.c:2090
 __x64_sys_io_submit+0x96/0xe0 fs/aio.c:2090
 x64_sys_call+0x3620/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:210
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable inline_vecs created at:
 aio_read+0x4c/0x690 fs/aio.c:1592
 io_submit_one+0x2809/0x3280 fs/aio.c:2061

CPU: 1 PID: 5053 Comm: syz-executor335 Not tainted 6.9.0-syzkaller-02707-g614da38e2f7a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
=====================================================


---
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Re: [syzbot] [PATCH] btrfs: Change iov_iter_alignment_iovec to check iovec count before accesses an iovec

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: [PATCH] btrfs: Change iov_iter_alignment_iovec to check iovec count before accesses an iovec
Author: dennis.lamerice@gmail.com

#syz test

Signed-off-by: Dennis Lam <dennis.lamerice@gmail.com>
---
 lib/iov_iter.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 4a6a9f419bd7..2d82ecf1b622 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -783,7 +783,7 @@ static unsigned long iov_iter_alignment_iovec(const struct iov_iter *i)
 	size_t size = i->count;
 	size_t skip = i->iov_offset;
 
-	do {
+	while(size) {
 		size_t len = iov->iov_len - skip;
 		if (len) {
 			res |= (unsigned long)iov->iov_base + skip;
@@ -794,7 +794,7 @@ static unsigned long iov_iter_alignment_iovec(const struct iov_iter *i)
 		}
 		iov++;
 		skip = 0;
-	} while (size);
+	} 
 	return res;
 }
 
-- 
2.45.2