[syzbot] [hfs?] KMSAN: uninit-value in hfs_iget

[syzbot] [hfs?] KMSAN: uninit-value in hfs_iget

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    af9c191ac2a0 Merge tag 'trace-ring-buffer-v6.12' of git://..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1705c107980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=547de13ee0a4d284
dashboard link: https://syzkaller.appspot.com/bug?extid=18dd03a3fcf0ffe27da0
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=1085c107980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16aa9c27980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2fd24309dcaf/disk-af9c191a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/37cd070c7ff6/vmlinux-af9c191a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/71a3466b8e96/bzImage-af9c191a.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/28d1a4936640/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+18dd03a3fcf0ffe27da0@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 64
=====================================================
BUG: KMSAN: uninit-value in hfs_iget+0x1be/0x240 fs/hfs/inode.c:403
 hfs_iget+0x1be/0x240 fs/hfs/inode.c:403
 hfs_lookup+0x2f3/0x3d0 fs/hfs/dir.c:37
 lookup_one_qstr_excl+0x238/0x530 fs/namei.c:1633
 do_unlinkat+0x2c5/0xe10 fs/namei.c:4521
 __do_sys_unlinkat fs/namei.c:4576 [inline]
 __se_sys_unlinkat fs/namei.c:4569 [inline]
 __x64_sys_unlinkat+0x17a/0x220 fs/namei.c:4569
 x64_sys_call+0x2c7a/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:264
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable rec created at:
 hfs_lookup+0x43/0x3d0 fs/hfs/dir.c:23
 lookup_one_qstr_excl+0x238/0x530 fs/namei.c:1633

CPU: 1 UID: 0 PID: 5180 Comm: syz-executor419 Not tainted 6.11.0-syzkaller-08829-gaf9c191ac2a0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
=====================================================


---
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If the report is already addressed, let syzbot know by replying with:
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Re: [syzbot] [hfs?] KMSAN: uninit-value in hfs_iget

[Edward Adam Davis]

When the read data is insufficient to fill the rec, use 0 to fill it

#syz test

diff --git a/fs/hfs/bfind.c b/fs/hfs/bfind.c
index ef9498a6e88a..f0292b76e3d4 100644
--- a/fs/hfs/bfind.c
+++ b/fs/hfs/bfind.c
@@ -168,6 +168,8 @@ int hfs_brec_read(struct hfs_find_data *fd, void *rec, int rec_len)
 	if (fd->entrylength > rec_len)
 		return -EINVAL;
 	hfs_bnode_read(fd->bnode, rec, fd->entryoffset, fd->entrylength);
+	if (rec_len > fd->entrylength)
+		memset(rec + fd->entrylength, 0, rec_len - fd->entrylength);
 	return 0;
 }
 

Re: [syzbot] [hfs?] KMSAN: uninit-value in hfs_iget

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+18dd03a3fcf0ffe27da0@syzkaller.appspotmail.com
Tested-by: syzbot+18dd03a3fcf0ffe27da0@syzkaller.appspotmail.com

Tested on:

commit:         de5cb0dc Merge branch 'address-masking'
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1374619f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=547de13ee0a4d284
dashboard link: https://syzkaller.appspot.com/bug?extid=18dd03a3fcf0ffe27da0
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=178e858b980000

Note: testing is done by a robot and is best-effort only.