+ mm-khugepaged-fix-kernel-bug-in-hpage_collapse_scan_file.patch added to mm-hotfixes-unstable branch

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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

This patch will shortly appear at

This patch will later appear in the mm-hotfixes-unstable branch at

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From: Ivan Orlov <ivan.orlov0322@xxxxxxxxx>
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:
 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

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@xxxxxxxxx
Link: https://syzkaller.appspot.com/bug?id=7d6bb3760e026ece7524500fe44fb024a0e959fc
Signed-off-by: Ivan Orlov <ivan.orlov0322@xxxxxxxxx>
Reported-by: syzbot+9578faa5475acb35fa50@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Himadri Pandya <himadrispandya@xxxxxxxxx>
Cc: Ivan Orlov <ivan.orlov0322@xxxxxxxxx>
Cc: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
Cc: Song Liu <songliubraving@xxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

 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 {
@@ -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;
+				}

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


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