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SubjectKASAN: use-after-scope in ext4_group_desc_csum
Date
Hi,

I'm getting below warning when I enable CONFIG_KASAN_EXTRA=y on a arm64 ThunderX2 system.
As far as I can tell this is present since KASAN_EXTRA was introduced (4.16).

[ 64.547333] ==================================================================
[ 64.561933] BUG: KASAN: use-after-scope in ext4_es_lookup_extent+0x130/0x980
[ 64.576105] Write of size 4 at addr ffff80222d81f0ec by task exe/4075

[ 64.592044] CPU: 102 PID: 4075 Comm: exe Not tainted 4.19.0-rc6-jang+ #29
[ 64.605690] Hardware name: To be filled by O.E.M. Saber/To be filled by O.E.M., BIOS 0ACKL018 03/30/2018
[ 64.624750] Call trace:
[ 64.629666] dump_backtrace+0x0/0x360
[ 64.637024] show_stack+0x24/0x30
[ 64.643687] dump_stack+0x12c/0x1b4
[ 64.650699] print_address_description+0x68/0x2c8
[ 64.660152] kasan_report+0x130/0x300
[ 64.667509] __asan_store4+0x84/0xa8
[ 64.674693] ext4_es_lookup_extent+0x130/0x980
[ 64.683623] ext4_map_blocks+0xe0/0x990
[ 64.691330] _ext4_get_block+0x130/0x2b8
[ 64.699211] ext4_get_block+0x40/0x50
[ 64.706571] generic_block_bmap+0x104/0x178
[ 64.714977] ext4_bmap+0xc4/0x198
[ 64.721636] bmap+0x54/0x70
[ 64.727250] jbd2_journal_init_inode+0x2c/0x208
[ 64.736355] ext4_fill_super+0x5080/0x5c90
[ 64.744587] mount_bdev+0x1e0/0x228
[ 64.751597] ext4_mount+0x44/0x58
[ 64.758255] mount_fs+0x58/0x1b8
[ 64.764740] vfs_kern_mount.part.2+0xc0/0x2a8
[ 64.773495] do_mount+0x7a8/0x13e8
[ 64.780327] ksys_mount+0x9c/0x110
[ 64.787160] __arm64_sys_mount+0x70/0x88
[ 64.795043] el0_svc_handler+0xac/0x150
[ 64.802749] el0_svc+0x8/0xc

[ 64.811521] The buggy address belongs to the page:
[ 64.821149] page:ffff7e0088b607c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
[ 64.837249] flags: 0x1ffff00000000000()
[ 64.844959] raw: 1ffff00000000000 ffff7e0088b607c8 ffff7e0088b607c8 0000000000000000
[ 64.860527] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[ 64.876093] page dumped because: kasan: bad access detected

[ 64.890278] Memory state around the buggy address:
[ 64.899907] ffff80222d81ef80: f2 f2 f2 f2 00 f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2
[ 64.914426] ffff80222d81f000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
[ 64.928945] >ffff80222d81f080: f8 f8 f8 f8 f8 f8 f1 f1 f1 f1 f8 f8 f8 f8 00 f2
[ 64.943463] ^
[ 64.956759] ffff80222d81f100: f2 f2 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
[ 64.971278] ffff80222d81f180: f8 f8 f8 f8 f1 f1 f1 f1 00 00 00 f2 f8 f8 f8 f8
[ 64.985795] ==================================================================
[ 65.000312] Disabling lock debugging due to kernel taint
[ 65.037509] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts: (null)

I'm not seeing any issues like filesystem corruption or misbehaviour that could be related
the warning.

Is this a false positive? Any thoughts?

--Jan

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