[syzbot] [mm?] KMSAN: uninit-value in swap_writepage

Hello,

syzbot found the following issue on:

HEAD commit: fc20a3e57247 Merge tag 'for-linus-6.12a-rc2-tag' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11cdfd27980000
kernel config: https://syzkaller.appspot.com/x/.config?x=d302f14701986aa0
dashboard link: https://syzkaller.appspot.com/bug?extid=febb2473441bfb8fb380
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5b4b9aca7b75/disk-fc20a3e5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b22e17636ec0/vmlinux-fc20a3e5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5266e625be99/bzImage-fc20a3e5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

=====================================================
BUG: KMSAN: uninit-value in is_folio_zero_filled mm/page_io.c:189 [inline]
BUG: KMSAN: uninit-value in swap_writepage+0x536/0x12b0 mm/page_io.c:259
is_folio_zero_filled mm/page_io.c:189 [inline]
swap_writepage+0x536/0x12b0 mm/page_io.c:259
shmem_writepage+0x2117/0x2450 mm/shmem.c:1567
pageout mm/vmscan.c:688 [inline]
shrink_folio_list+0x5e78/0x7dd0 mm/vmscan.c:1366
evict_folios+0x9813/0xbaf0 mm/vmscan.c:4583
try_to_shrink_lruvec+0x13a3/0x1750 mm/vmscan.c:4778
shrink_one+0x646/0xd20 mm/vmscan.c:4816
shrink_many mm/vmscan.c:4879 [inline]
lru_gen_shrink_node mm/vmscan.c:4957 [inline]
shrink_node+0x451a/0x50f0 mm/vmscan.c:5937
kswapd_shrink_node mm/vmscan.c:6765 [inline]
balance_pgdat mm/vmscan.c:6957 [inline]
kswapd+0x25e2/0x42f0 mm/vmscan.c:7226
kthread+0x3e2/0x540 kernel/kthread.c:389
ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Uninit was created at:
__alloc_pages_noprof+0x9d6/0xe70 mm/page_alloc.c:4756
alloc_pages_mpol_noprof+0x299/0x990 mm/mempolicy.c:2265
folio_alloc_mpol_noprof+0x55/0x180 mm/mempolicy.c:2283
shmem_alloc_folio mm/shmem.c:1774 [inline]
shmem_alloc_and_add_folio+0xc33/0x1c30 mm/shmem.c:1813
shmem_get_folio_gfp+0xacd/0x1f30 mm/shmem.c:2335
shmem_get_folio mm/shmem.c:2441 [inline]
shmem_symlink+0x528/0xa20 mm/shmem.c:3834
vfs_symlink+0x1ed/0x460 fs/namei.c:4615
do_symlinkat+0x257/0x8a0 fs/namei.c:4641
__do_sys_symlink fs/namei.c:4662 [inline]
__se_sys_symlink fs/namei.c:4660 [inline]
__x64_sys_symlink+0xe0/0x140 fs/namei.c:4660
x64_sys_call+0x30e8/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:89
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

CPU: 1 UID: 0 PID: 80 Comm: kswapd0 Tainted: G W 6.12.0-rc1-syzkaller-00330-gfc20a3e57247 #0
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
=====================================================


---
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Thanks. I'm guessing that shmem symlinks aren't initializing the whole
page (folio) and that has tripped up Usama's "store zero pages to be
swapped out in a bitmap" feature - it's checking the uninitialized part
of the page for zeroness.

This is a very similar bug to the one in https://lore.kernel.org/all/[email protected]/
(Thanks Nhat for pointing this out!)

As Hugh mentioned in that thread, its likely not a bug in (z)swap.

Its just working with the folio that was given to it, and it should probably be
initialized before swap_writepage is called.

I havent worked on shmem code before, but will try to have a look.
Hugh mentioned in the other thread that shmem can keep uninitialized
data pages around, but should be zeroing what's still uninitialized before
it can reach the outside world. Maybeshmem_symlink gets a folio
that wasnt initialized?

Thanks,
Usama

syzbot has found a reproducer for the following issue on:

HEAD commit: 493f3f38da21 Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=102582a4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f20bce78db15972a
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=142f5b18580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7b55c1bb607a/disk-493f3f38.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dc5eaf46c59e/vmlinux-493f3f38.xz
kernel image: https://storage.googleapis.com/syzbot-assets/314f12332ac4/bzImage-493f3f38.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/07ee34a1a626/mount_2.gz
fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=141291b0580000)
BUG: KMSAN: uninit-value in is_folio_zero_filled mm/page_io.c:188 [inline]
BUG: KMSAN: uninit-value in swap_writepage+0x547/0x1950 mm/page_io.c:266
is_folio_zero_filled mm/page_io.c:188 [inline]
swap_writepage+0x547/0x1950 mm/page_io.c:266
shmem_writepage+0x2360/0x25a0 mm/shmem.c:1647
pageout mm/vmscan.c:696 [inline]
shrink_folio_list+0x5dd2/0x8220 mm/vmscan.c:1402
evict_folios+0x94ed/0xb9c0 mm/vmscan.c:4660
try_to_shrink_lruvec+0xc58/0x1080 mm/vmscan.c:4821
lru_gen_shrink_lruvec mm/vmscan.c:4970 [inline]
shrink_lruvec+0x49a/0x47c0 mm/vmscan.c:5715
shrink_node_memcgs mm/vmscan.c:5951 [inline]
shrink_node+0x105e/0x51c0 mm/vmscan.c:5992
shrink_zones mm/vmscan.c:6237 [inline]
do_try_to_free_pages+0x820/0x2550 mm/vmscan.c:6299
try_to_free_mem_cgroup_pages+0x3fa/0xa60 mm/vmscan.c:6631
try_charge_memcg+0x71a/0x1780 mm/memcontrol.c:2255
obj_cgroup_charge_pages+0x2cb/0x640 mm/memcontrol.c:2636
__memcg_kmem_charge_page+0x151/0x520 mm/memcontrol.c:2663
__alloc_frozen_pages_noprof+0x93d/0xe00 mm/page_alloc.c:4756
alloc_pages_mpol+0x4cd/0x890 mm/mempolicy.c:2270
alloc_frozen_pages_noprof mm/mempolicy.c:2341 [inline]
alloc_pages_noprof+0x1b5/0x250 mm/mempolicy.c:2361
io_mem_alloc_compound io_uring/memmap.c:29 [inline]
io_region_allocate_pages+0x168/0x8b0 io_uring/memmap.c:167
io_create_region+0x6eb/0x810 io_uring/memmap.c:223
io_allocate_scq_urings+0x3a2/0xa50 io_uring/io_uring.c:3479
io_uring_create+0xabc/0x1440 io_uring/io_uring.c:3701
io_uring_setup io_uring/io_uring.c:3791 [inline]
__do_sys_io_uring_setup io_uring/io_uring.c:3818 [inline]
__se_sys_io_uring_setup+0x476/0x4d0 io_uring/io_uring.c:3812
__x64_sys_io_uring_setup+0x6c/0xa0 io_uring/io_uring.c:3812
x64_sys_call+0x2e82/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:426
Uninit was stored to memory at:
memcpy_from_iter lib/iov_iter.c:73 [inline]
iterate_bvec include/linux/iov_iter.h:123 [inline]
iterate_and_advance2 include/linux/iov_iter.h:304 [inline]
iterate_and_advance include/linux/iov_iter.h:328 [inline]
__copy_from_iter lib/iov_iter.c:249 [inline]
copy_page_from_iter_atomic+0x1299/0x30c0 lib/iov_iter.c:483
copy_folio_from_iter_atomic include/linux/uio.h:210 [inline]
generic_perform_write+0x8d1/0x1080 mm/filemap.c:4201
shmem_file_write_iter+0x2ba/0x2f0 mm/shmem.c:3454
do_iter_readv_writev+0x93a/0xbc0
vfs_iter_write+0x44d/0xd60 fs/read_write.c:974
lo_write_bvec drivers/block/loop.c:245 [inline]
lo_write_simple drivers/block/loop.c:266 [inline]
do_req_filebacked drivers/block/loop.c:520 [inline]
loop_handle_cmd drivers/block/loop.c:1929 [inline]
loop_process_work+0x15fb/0x3760 drivers/block/loop.c:1964
loop_workfn+0x48/0x60 drivers/block/loop.c:1988
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0xae0/0x1c40 kernel/workqueue.c:3317
worker_thread+0xea7/0x14f0 kernel/workqueue.c:3398
kthread+0x6b9/0xef0 kernel/kthread.c:464
ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:148
__alloc_frozen_pages_noprof+0x9a7/0xe00 mm/page_alloc.c:4762
__alloc_pages_noprof mm/page_alloc.c:4773 [inline]
alloc_pages_bulk_noprof+0x1227/0x1a60 mm/page_alloc.c:4693
btrfs_alloc_page_array fs/btrfs/extent_io.c:632 [inline]
alloc_eb_folio_array+0x199/0x750 fs/btrfs/extent_io.c:656
alloc_extent_buffer+0x76a/0x36f0 fs/btrfs/extent_io.c:3092
btrfs_find_create_tree_block+0x46/0x60 fs/btrfs/disk-io.c:614
btrfs_init_new_buffer fs/btrfs/extent-tree.c:5017 [inline]
btrfs_alloc_tree_block+0x415/0x1990 fs/btrfs/extent-tree.c:5130
btrfs_alloc_log_tree_node fs/btrfs/disk-io.c:950 [inline]
btrfs_add_log_tree+0x1b7/0x7a0 fs/btrfs/disk-io.c:998
start_log_trans fs/btrfs/tree-log.c:227 [inline]
btrfs_log_inode_parent+0xa87/0x1c30 fs/btrfs/tree-log.c:7097
btrfs_log_dentry_safe+0x9a/0x100 fs/btrfs/tree-log.c:7202
btrfs_sync_file+0x1676/0x2180 fs/btrfs/file.c:1649
vfs_fsync_range+0x1f9/0x260 fs/sync.c:187
generic_write_sync include/linux/fs.h:2970 [inline]
btrfs_do_write_iter+0xabe/0xcb0 fs/btrfs/file.c:1386
btrfs_file_write_iter+0x38/0x50 fs/btrfs/file.c:1396
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0xb34/0x1540 fs/read_write.c:679
ksys_write+0x240/0x4b0 fs/read_write.c:731
__do_sys_write fs/read_write.c:742 [inline]
__se_sys_write fs/read_write.c:739 [inline]
__x64_sys_write+0x93/0xe0 fs/read_write.c:739
x64_sys_call+0x3161/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:2
CPU: 0 UID: 0 PID: 6322 Comm: syz.0.26 Not tainted 6.14.0-rc1-syzkaller-00224-g493f3f38da21 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
=====================================================


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