ext4: fix uninititialized value in 'ext4_evict_inode'

In the Linux kernel, the following vulnerability has been resolved:

ext4: fix uninititialized value in 'ext4_evict_inode'

Syzbot found the following issue:

=====================================================

BUG: KMSAN: uninit-value in ext4_evict_inode+0xdd/0x26b0 fs/ext4/inode.c:180

ext4_evict_inode+0xdd/0x26b0 fs/ext4/inode.c:180

evict+0x365/0x9a0 fs/inode.c:664

iput_final fs/inode.c:1747 [inline]

iput+0x985/0xdd0 fs/inode.c:1773

__ext4_new_inode+0xe54/0x7ec0 fs/ext4/ialloc.c:1361

ext4_mknod+0x376/0x840 fs/ext4/namei.c:2844

vfs_mknod+0x79d/0x830 fs/namei.c:3914

do_mknodat+0x47d/0xaa0

__do_sys_mknodat fs/namei.c:3992 [inline]

__se_sys_mknodat fs/namei.c:3989 [inline]

__ia32_sys_mknodat+0xeb/0x150 fs/namei.c:3989

do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]

__do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178

do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203

do_SYSENTER_32+0x1b/0x20 arch/x86/entry/common.c:246

entry_SYSENTER_compat_after_hwframe+0x70/0x82

Uninit was created at:

__alloc_pages+0x9f1/0xe80 mm/page_alloc.c:5578

alloc_pages+0xaae/0xd80 mm/mempolicy.c:2285

alloc_slab_page mm/slub.c:1794 [inline]

allocate_slab+0x1b5/0x1010 mm/slub.c:1939

new_slab mm/slub.c:1992 [inline]

___slab_alloc+0x10c3/0x2d60 mm/slub.c:3180

__slab_alloc mm/slub.c:3279 [inline]

slab_alloc_node mm/slub.c:3364 [inline]

slab_alloc mm/slub.c:3406 [inline]

__kmem_cache_alloc_lru mm/slub.c:3413 [inline]

kmem_cache_alloc_lru+0x6f3/0xb30 mm/slub.c:3429

alloc_inode_sb include/linux/fs.h:3117 [inline]

ext4_alloc_inode+0x5f/0x860 fs/ext4/super.c:1321

alloc_inode+0x83/0x440 fs/inode.c:259

new_inode_pseudo fs/inode.c:1018 [inline]

new_inode+0x3b/0x430 fs/inode.c:1046

__ext4_new_inode+0x2a7/0x7ec0 fs/ext4/ialloc.c:959

ext4_mkdir+0x4d5/0x1560 fs/ext4/namei.c:2992

vfs_mkdir+0x62a/0x870 fs/namei.c:4035

do_mkdirat+0x466/0x7b0 fs/namei.c:4060

__do_sys_mkdirat fs/namei.c:4075 [inline]

__se_sys_mkdirat fs/namei.c:4073 [inline]

__ia32_sys_mkdirat+0xc4/0x120 fs/namei.c:4073

do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]

__do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178

do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203

do_SYSENTER_32+0x1b/0x20 arch/x86/entry/common.c:246

entry_SYSENTER_compat_after_hwframe+0x70/0x82

CPU: 1 PID: 4625 Comm: syz-executor.2 Not tainted 6.1.0-rc4-syzkaller-62821-gcb231e2f67ec #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022

=====================================================

Now, 'ext4_alloc_inode()' didn't init 'ei->i_flags'. If new inode failed

before set 'ei->i_flags' in '__ext4_new_inode()', then do 'iput()'. As after

6bc0d63dad7f commit will access 'ei->i_flags' in 'ext4_evict_inode()' which

will lead to access uninit-value.

To solve above issue just init 'ei->i_flags' in 'ext4_alloc_inode()'.