KMSAN: uninit-value in fat_evict_inode

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 8bbbc5cf kmsan: don't compile memmove
git tree: https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=12c5fdede00000
kernel config: https://syzkaller.appspot.com/x/.config?x=cd0e9a6b0e555cc3
dashboard link: https://syzkaller.appspot.com/bug?extid=9d82b8de2992579da5d0
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
userspace arch: i386

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+9d82b8...@syzkaller.appspotmail.com

FAT-fs (loop2): Invalid FSINFO signature: 0x00000000, 0x00000000 (sector = 1)
FAT-fs (loop2): error, fat_get_cluster: invalid start cluster (i_pos 1, start bb1414ac)
FAT-fs (loop2): Filesystem has been set read-only
=====================================================
BUG: KMSAN: uninit-value in fat_free_eofblocks fs/fat/inode.c:628 [inline]
BUG: KMSAN: uninit-value in fat_evict_inode+0x2f4/0x920 fs/fat/inode.c:658
CPU: 0 PID: 9035 Comm: syz-executor.2 Not tainted 5.6.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c9/0x220 lib/dump_stack.c:118
kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118
__msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
fat_free_eofblocks fs/fat/inode.c:628 [inline]
fat_evict_inode+0x2f4/0x920 fs/fat/inode.c:658
evict+0x4ab/0xe10 fs/inode.c:575
iput_final fs/inode.c:1571 [inline]
iput+0xa70/0xe10 fs/inode.c:1597
fat_fill_super+0x7b5c/0x89b0 fs/fat/inode.c:1865
vfat_fill_super+0xa6/0xc0 fs/fat/namei_vfat.c:1050
mount_bdev+0x654/0x880 fs/super.c:1417
vfat_mount+0xc9/0xe0 fs/fat/namei_vfat.c:1057
legacy_get_tree+0x169/0x2e0 fs/fs_context.c:622
vfs_get_tree+0xdd/0x580 fs/super.c:1547
do_new_mount fs/namespace.c:2822 [inline]
do_mount+0x365c/0x4ac0 fs/namespace.c:3107
__do_compat_sys_mount fs/compat.c:122 [inline]
__se_compat_sys_mount+0x3a8/0xa10 fs/compat.c:89
__ia32_compat_sys_mount+0x157/0x1b0 fs/compat.c:89
do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline]
do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410
entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f11d99
Code: 90 e8 0b 00 00 00 f3 90 0f ae e8 eb f9 8d 74 26 00 89 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f5d0bef0 EFLAGS: 00000296 ORIG_RAX: 0000000000000015
RAX: ffffffffffffffda RBX: 00000000f5d0bf8c RCX: 0000000020000380
RDX: 00000000f5d0bf6c RSI: 0000000000000000 RDI: 00000000f5d0bfcc
RBP: 00000000f5d0c168 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Uninit was created at:
kmsan_save_stack_with_flags+0x3c/0x90 mm/kmsan/kmsan.c:144
kmsan_internal_alloc_meta_for_pages mm/kmsan/kmsan_shadow.c:307 [inline]
kmsan_alloc_page+0x12a/0x310 mm/kmsan/kmsan_shadow.c:336
__alloc_pages_nodemask+0x5712/0x5e80 mm/page_alloc.c:4775
alloc_pages_current+0x67d/0x990 mm/mempolicy.c:2211
alloc_pages include/linux/gfp.h:534 [inline]
alloc_slab_page+0x111/0x12f0 mm/slub.c:1530
allocate_slab mm/slub.c:1675 [inline]
new_slab+0x2bc/0x1130 mm/slub.c:1741
new_slab_objects mm/slub.c:2492 [inline]
___slab_alloc+0x1533/0x1f30 mm/slub.c:2643
__slab_alloc mm/slub.c:2683 [inline]
slab_alloc_node mm/slub.c:2757 [inline]
slab_alloc mm/slub.c:2802 [inline]
kmem_cache_alloc+0xb23/0xd70 mm/slub.c:2807
fat_alloc_inode+0x58/0x120 fs/fat/inode.c:748
alloc_inode fs/inode.c:231 [inline]
new_inode_pseudo+0xb1/0x590 fs/inode.c:927
new_inode+0x5a/0x3d0 fs/inode.c:956
fat_fill_super+0x634b/0x89b0 fs/fat/inode.c:1844
vfat_fill_super+0xa6/0xc0 fs/fat/namei_vfat.c:1050
mount_bdev+0x654/0x880 fs/super.c:1417
vfat_mount+0xc9/0xe0 fs/fat/namei_vfat.c:1057
legacy_get_tree+0x169/0x2e0 fs/fs_context.c:622
vfs_get_tree+0xdd/0x580 fs/super.c:1547
do_new_mount fs/namespace.c:2822 [inline]
do_mount+0x365c/0x4ac0 fs/namespace.c:3107
__do_compat_sys_mount fs/compat.c:122 [inline]
__se_compat_sys_mount+0x3a8/0xa10 fs/compat.c:89
__ia32_compat_sys_mount+0x157/0x1b0 fs/compat.c:89
do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline]
do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410
entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139
=====================================================


---
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[OGAWA Hirofumi]

When got error at middle of reading inode, some fields in inode
might be still not initialized. And then evict_inode path may access
those fields via iput().

To fix, this makes sure that inode fields are initialized.

Reported-by: syzbot+9d82b8...@syzkaller.appspotmail.com
Cc: sta...@vger.kernel.org
Signed-off-by: OGAWA Hirofumi <hiro...@mail.parknet.co.jp>
---
fs/fat/inode.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 5f04c5c..686130f 100644
--- a/fs/fat/inode.c 2020-02-09 21:29:07.541357068 +0900
+++ b/fs/fat/inode.c 2020-02-22 02:15:20.451313122 +0900
@@ -749,6 +749,13 @@ static struct inode *fat_alloc_inode(str
return NULL;

init_rwsem(&ei->truncate_lock);
+ /* Zeroing to allow iput() even if partial initialized inode. */
+ ei->mmu_private = 0;
+ ei->i_start = 0;
+ ei->i_logstart = 0;
+ ei->i_attrs = 0;
+ ei->i_pos = 0;
+
return &ei->vfs_inode;
}

@@ -1373,16 +1380,6 @@ out:
return 0;
}

-static void fat_dummy_inode_init(struct inode *inode)
-{
- /* Initialize this dummy inode to work as no-op. */
- MSDOS_I(inode)->mmu_private = 0;
- MSDOS_I(inode)->i_start = 0;
- MSDOS_I(inode)->i_logstart = 0;
- MSDOS_I(inode)->i_attrs = 0;
- MSDOS_I(inode)->i_pos = 0;
-}
-
static int fat_read_root(struct inode *inode)
{
struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
@@ -1843,13 +1840,11 @@ int fat_fill_super(struct super_block *s
fat_inode = new_inode(sb);
if (!fat_inode)
goto out_fail;
- fat_dummy_inode_init(fat_inode);
sbi->fat_inode = fat_inode;

fsinfo_inode = new_inode(sb);
if (!fsinfo_inode)
goto out_fail;
- fat_dummy_inode_init(fsinfo_inode);
fsinfo_inode->i_ino = MSDOS_FSINFO_INO;
sbi->fsinfo_inode = fsinfo_inode;
insert_inode_hash(fsinfo_inode);
_

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: 8bbbc5cf kmsan: don't compile memmove
git tree: https://github.com/google/kmsan.git master

console output: https://syzkaller.appspot.com/x/log.txt?x=11c3774ee00000

kernel config: https://syzkaller.appspot.com/x/.config?x=cd0e9a6b0e555cc3
dashboard link: https://syzkaller.appspot.com/bug?extid=9d82b8de2992579da5d0
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
userspace arch: i386

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=171ce265e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15bb1109e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+9d82b8...@syzkaller.appspotmail.com

FAT-fs (loop0): error, invalid access to FAT (entry 0x00006500)
FAT-fs (loop0): Filesystem has been set read-only

=====================================================
BUG: KMSAN: uninit-value in fat_free_eofblocks fs/fat/inode.c:628 [inline]
BUG: KMSAN: uninit-value in fat_evict_inode+0x2f4/0x920 fs/fat/inode.c:658

CPU: 0 PID: 11199 Comm: syz-executor375 Not tainted 5.6.0-rc2-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c9/0x220 lib/dump_stack.c:118
kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118
__msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
fat_free_eofblocks fs/fat/inode.c:628 [inline]
fat_evict_inode+0x2f4/0x920 fs/fat/inode.c:658
evict+0x4ab/0xe10 fs/inode.c:575
iput_final fs/inode.c:1571 [inline]
iput+0xa70/0xe10 fs/inode.c:1597

fat_build_inode+0x6a3/0x840 fs/fat/inode.c:610
vfat_mkdir+0x547/0x7d0 fs/fat/namei_vfat.c:871
vfs_mkdir+0x691/0x920 fs/namei.c:3889
do_mkdirat+0x39f/0x680 fs/namei.c:3912
__do_sys_mkdir fs/namei.c:3928 [inline]
__se_sys_mkdir fs/namei.c:3926 [inline]
__ia32_sys_mkdir+0x9f/0xd0 fs/namei.c:3926

do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline]
do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410
entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139

RIP: 0023:0xf7f1bd99

Code: 90 e8 0b 00 00 00 f3 90 0f ae e8 eb f9 8d 74 26 00 89 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90

RSP: 002b:00000000ffb4ff4c EFLAGS: 00000292 ORIG_RAX: 0000000000000027
RAX: ffffffffffffffda RBX: 0000000020000740 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 00000000ffb4ffbe RDI: 0000000000000001
RBP: 00000000000000c2 R08: 0000000000000000 R09: 0000000000000000