The patch titled Subject: mm: khugepaged: fix kernel BUG in hpage_collapse_scan_file() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-khugepaged-fix-kernel-bug-in-hpage_collapse_scan_file.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ivan Orlov ivan.orlov0322@gmail.com Subject: mm: khugepaged: fix kernel BUG in hpage_collapse_scan_file() Date: Wed, 29 Mar 2023 18:53:30 +0400

Syzkaller reported the following issue:

kernel BUG at mm/khugepaged.c:1823! invalid opcode: 0000 [#1] PREEMPT SMP KASAN CPU: 1 PID: 5097 Comm: syz-executor220 Not tainted 6.2.0-syzkaller-13154-g857f1268a591 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/16/2023 RIP: 0010:collapse_file mm/khugepaged.c:1823 [inline] RIP: 0010:hpage_collapse_scan_file+0x67c8/0x7580 mm/khugepaged.c:2233 Code: 00 00 89 de e8 c9 66 a3 ff 31 ff 89 de e8 c0 66 a3 ff 45 84 f6 0f 85 28 0d 00 00 e8 22 64 a3 ff e9 dc f7 ff ff e8 18 64 a3 ff <0f> 0b f3 0f 1e fa e8 0d 64 a3 ff e9 93 f6 ff ff f3 0f 1e fa 4c 89 RSP: 0018:ffffc90003dff4e0 EFLAGS: 00010093 RAX: ffffffff81e95988 RBX: 00000000000001c1 RCX: ffff8880205b3a80 RDX: 0000000000000000 RSI: 00000000000001c0 RDI: 00000000000001c1 RBP: ffffc90003dff830 R08: ffffffff81e90e67 R09: fffffbfff1a433c3 R10: 0000000000000000 R11: dffffc0000000001 R12: 0000000000000000 R13: ffffc90003dff6c0 R14: 00000000000001c0 R15: 0000000000000000 FS: 00007fdbae5ee700(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fdbae6901e0 CR3: 000000007b2dd000 CR4: 00000000003506e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> madvise_collapse+0x721/0xf50 mm/khugepaged.c:2693 madvise_vma_behavior mm/madvise.c:1086 [inline] madvise_walk_vmas mm/madvise.c:1260 [inline] do_madvise+0x9e5/0x4680 mm/madvise.c:1439 __do_sys_madvise mm/madvise.c:1452 [inline] __se_sys_madvise mm/madvise.c:1450 [inline] __x64_sys_madvise+0xa5/0xb0 mm/madvise.c:1450 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd

The xas_store() call during page cache scanning can potentially translate 'xas' into the error state (with the reproducer provided by the syzkaller the error code is -ENOMEM). However, there are no further checks after the 'xas_store', and the next call of 'xas_next' at the start of the scanning cycle doesn't increase the xa_index, and the issue occurs.

This patch will add the xarray state error checking after the xas_store() and the corresponding result error code.

Tested via syzbot.

Link: https://lkml.kernel.org/r/20230329145330.23191-1-ivan.orlov0322@gmail.com Link: https://syzkaller.appspot.com/bug?id=7d6bb3760e026ece7524500fe44fb024a0e959f... Signed-off-by: Ivan Orlov ivan.orlov0322@gmail.com Reported-by: syzbot+9578faa5475acb35fa50@syzkaller.appspotmail.com Cc: Himadri Pandya himadrispandya@gmail.com Cc: Ivan Orlov ivan.orlov0322@gmail.com Cc: Shuah Khan skhan@linuxfoundation.org Cc: Song Liu songliubraving@fb.com Cc: Rik van Riel riel@surriel.com Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/khugepaged.c | 10 ++++++++++ 1 file changed, 10 insertions(+)

--- a/mm/khugepaged.c~mm-khugepaged-fix-kernel-bug-in-hpage_collapse_scan_file +++ a/mm/khugepaged.c @@ -55,6 +55,7 @@ enum scan_result { SCAN_CGROUP_CHARGE_FAIL, SCAN_TRUNCATED, SCAN_PAGE_HAS_PRIVATE, + SCAN_STORE_FAILED, };

#define CREATE_TRACE_POINTS @@ -1840,6 +1841,15 @@ static int collapse_file(struct mm_struc goto xa_locked; } xas_store(&xas, hpage); + if (xas_error(&xas)) { + /* revert shmem_charge performed + * in the previous condition + */ + mapping->nrpages--; + shmem_uncharge(mapping->host, 1); + result = SCAN_STORE_FAILED; + goto xa_locked; + } nr_none++; continue; } _

Patches currently in -mm which might be from ivan.orlov0322@gmail.com are

mm-khugepaged-fix-kernel-bug-in-hpage_collapse_scan_file.patch