syzbot

loop0: detected capacity change from 0 to 15
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BUG: KMSAN: uninit-value in cont_expand_zero fs/buffer.c:2428 [inline]
BUG: KMSAN: uninit-value in cont_write_begin+0xd84/0xdc0 fs/buffer.c:2453
 cont_expand_zero fs/buffer.c:2428 [inline]
 cont_write_begin+0xd84/0xdc0 fs/buffer.c:2453
 fat_write_begin+0x92/0x260 fs/fat/inode.c:235
 pagecache_write_begin+0x82/0xa0 mm/filemap.c:3631
 generic_cont_expand_simple+0x11a/0x2c0 fs/buffer.c:2355
 fat_cont_expand+0x78/0x470 fs/fat/file.c:223
 fat_setattr+0xab1/0x1b70 fs/fat/file.c:504
 notify_change+0x1f1c/0x2010 fs/attr.c:410
 do_truncate+0x238/0x2d0 fs/open.c:65
 do_sys_ftruncate+0x7d7/0xab0 fs/open.c:193
 __do_compat_sys_ftruncate fs/open.c:210 [inline]
 __se_compat_sys_ftruncate fs/open.c:208 [inline]
 __ia32_compat_sys_ftruncate+0x6c/0xa0 fs/open.c:208
 do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
 __do_fast_syscall_32+0x95/0xf0 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+0x4d/0x5c

Local variable fsdata.i created at:
 cont_write_begin+0xc1/0xdc0 fs/buffer.c:2453
 fat_write_begin+0x92/0x260 fs/fat/inode.c:235

CPU: 0 PID: 6846 Comm: syz-executor.0 Not tainted 5.18.0-syzkaller-16263-g2d0ce79ea812 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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