GHSA-CV9M-PRXM-594H
Vulnerability from github – Published: 2025-07-25 15:30 – Updated: 2025-11-18 21:32In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix race between async reclaim worker and close_ctree()
Syzbot reported an assertion failure due to an attempt to add a delayed iput after we have set BTRFS_FS_STATE_NO_DELAYED_IPUT in the fs_info state:
WARNING: CPU: 0 PID: 65 at fs/btrfs/inode.c:3420 btrfs_add_delayed_iput+0x2f8/0x370 fs/btrfs/inode.c:3420 Modules linked in: CPU: 0 UID: 0 PID: 65 Comm: kworker/u8:4 Not tainted 6.15.0-next-20250530-syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Workqueue: btrfs-endio-write btrfs_work_helper RIP: 0010:btrfs_add_delayed_iput+0x2f8/0x370 fs/btrfs/inode.c:3420 Code: 4e ad 5d (...) RSP: 0018:ffffc9000213f780 EFLAGS: 00010293 RAX: ffffffff83c635b7 RBX: ffff888058920000 RCX: ffff88801c769e00 RDX: 0000000000000000 RSI: 0000000000000100 RDI: 0000000000000000 RBP: 0000000000000001 R08: ffff888058921b67 R09: 1ffff1100b12436c R10: dffffc0000000000 R11: ffffed100b12436d R12: 0000000000000001 R13: dffffc0000000000 R14: ffff88807d748000 R15: 0000000000000100 FS: 0000000000000000(0000) GS:ffff888125c53000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00002000000bd038 CR3: 000000006a142000 CR4: 00000000003526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: btrfs_put_ordered_extent+0x19f/0x470 fs/btrfs/ordered-data.c:635 btrfs_finish_one_ordered+0x11d8/0x1b10 fs/btrfs/inode.c:3312 btrfs_work_helper+0x399/0xc20 fs/btrfs/async-thread.c:312 process_one_work kernel/workqueue.c:3238 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402 kthread+0x70e/0x8a0 kernel/kthread.c:464 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
This can happen due to a race with the async reclaim worker like this:
1) The async metadata reclaim worker enters shrink_delalloc(), which calls btrfs_start_delalloc_roots() with an nr_pages argument that has a value less than LONG_MAX, and that in turn enters start_delalloc_inodes(), which sets the local variable 'full_flush' to false because wbc->nr_to_write is less than LONG_MAX;
2) There it finds inode X in a root's delalloc list, grabs a reference for inode X (with igrab()), and triggers writeback for it with filemap_fdatawrite_wbc(), which creates an ordered extent for inode X;
3) The unmount sequence starts from another task, we enter close_ctree() and we flush the workqueue fs_info->endio_write_workers, which waits for the ordered extent for inode X to complete and when dropping the last reference of the ordered extent, with btrfs_put_ordered_extent(), when we call btrfs_add_delayed_iput() we don't add the inode to the list of delayed iputs because it has a refcount of 2, so we decrement it to 1 and return;
4) Shortly after at close_ctree() we call btrfs_run_delayed_iputs() which runs all delayed iputs, and then we set BTRFS_FS_STATE_NO_DELAYED_IPUT in the fs_info state;
5) The async reclaim worker, after calling filemap_fdatawrite_wbc(), now calls btrfs_add_delayed_iput() for inode X and there we trigger an assertion failure since the fs_info state has the flag BTRFS_FS_STATE_NO_DELAYED_IPUT set.
Fix this by setting BTRFS_FS_STATE_NO_DELAYED_IPUT only after we wait for the async reclaim workers to finish, after we call cancel_work_sync() for them at close_ctree(), and by running delayed iputs after wait for the reclaim workers to finish and before setting the bit.
This race was recently introduced by commit 19e60b2a95f5 ("btrfs: add extra warning if delayed iput is added when it's not allowed"). Without the new validation at btrfs_add_delayed_iput(), ---truncated---
{
"affected": [],
"aliases": [
"CVE-2025-38358"
],
"database_specific": {
"cwe_ids": [
"CWE-362"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-07-25T13:15:24Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix race between async reclaim worker and close_ctree()\n\nSyzbot reported an assertion failure due to an attempt to add a delayed\niput after we have set BTRFS_FS_STATE_NO_DELAYED_IPUT in the fs_info\nstate:\n\n WARNING: CPU: 0 PID: 65 at fs/btrfs/inode.c:3420 btrfs_add_delayed_iput+0x2f8/0x370 fs/btrfs/inode.c:3420\n Modules linked in:\n CPU: 0 UID: 0 PID: 65 Comm: kworker/u8:4 Not tainted 6.15.0-next-20250530-syzkaller #0 PREEMPT(full)\n Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025\n Workqueue: btrfs-endio-write btrfs_work_helper\n RIP: 0010:btrfs_add_delayed_iput+0x2f8/0x370 fs/btrfs/inode.c:3420\n Code: 4e ad 5d (...)\n RSP: 0018:ffffc9000213f780 EFLAGS: 00010293\n RAX: ffffffff83c635b7 RBX: ffff888058920000 RCX: ffff88801c769e00\n RDX: 0000000000000000 RSI: 0000000000000100 RDI: 0000000000000000\n RBP: 0000000000000001 R08: ffff888058921b67 R09: 1ffff1100b12436c\n R10: dffffc0000000000 R11: ffffed100b12436d R12: 0000000000000001\n R13: dffffc0000000000 R14: ffff88807d748000 R15: 0000000000000100\n FS: 0000000000000000(0000) GS:ffff888125c53000(0000) knlGS:0000000000000000\n CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: 00002000000bd038 CR3: 000000006a142000 CR4: 00000000003526f0\n DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\n DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\n Call Trace:\n \u003cTASK\u003e\n btrfs_put_ordered_extent+0x19f/0x470 fs/btrfs/ordered-data.c:635\n btrfs_finish_one_ordered+0x11d8/0x1b10 fs/btrfs/inode.c:3312\n btrfs_work_helper+0x399/0xc20 fs/btrfs/async-thread.c:312\n process_one_work kernel/workqueue.c:3238 [inline]\n process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321\n worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402\n kthread+0x70e/0x8a0 kernel/kthread.c:464\n ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148\n ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245\n \u003c/TASK\u003e\n\nThis can happen due to a race with the async reclaim worker like this:\n\n1) The async metadata reclaim worker enters shrink_delalloc(), which calls\n btrfs_start_delalloc_roots() with an nr_pages argument that has a value\n less than LONG_MAX, and that in turn enters start_delalloc_inodes(),\n which sets the local variable \u0027full_flush\u0027 to false because\n wbc-\u003enr_to_write is less than LONG_MAX;\n\n2) There it finds inode X in a root\u0027s delalloc list, grabs a reference for\n inode X (with igrab()), and triggers writeback for it with\n filemap_fdatawrite_wbc(), which creates an ordered extent for inode X;\n\n3) The unmount sequence starts from another task, we enter close_ctree()\n and we flush the workqueue fs_info-\u003eendio_write_workers, which waits\n for the ordered extent for inode X to complete and when dropping the\n last reference of the ordered extent, with btrfs_put_ordered_extent(),\n when we call btrfs_add_delayed_iput() we don\u0027t add the inode to the\n list of delayed iputs because it has a refcount of 2, so we decrement\n it to 1 and return;\n\n4) Shortly after at close_ctree() we call btrfs_run_delayed_iputs() which\n runs all delayed iputs, and then we set BTRFS_FS_STATE_NO_DELAYED_IPUT\n in the fs_info state;\n\n5) The async reclaim worker, after calling filemap_fdatawrite_wbc(), now\n calls btrfs_add_delayed_iput() for inode X and there we trigger an\n assertion failure since the fs_info state has the flag\n BTRFS_FS_STATE_NO_DELAYED_IPUT set.\n\nFix this by setting BTRFS_FS_STATE_NO_DELAYED_IPUT only after we wait for\nthe async reclaim workers to finish, after we call cancel_work_sync() for\nthem at close_ctree(), and by running delayed iputs after wait for the\nreclaim workers to finish and before setting the bit.\n\nThis race was recently introduced by commit 19e60b2a95f5 (\"btrfs: add\nextra warning if delayed iput is added when it\u0027s not allowed\"). Without\nthe new validation at btrfs_add_delayed_iput(), \n---truncated---",
"id": "GHSA-cv9m-prxm-594h",
"modified": "2025-11-18T21:32:29Z",
"published": "2025-07-25T15:30:51Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-38358"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4693cda2c06039c875f2eef0123b22340c34bfa0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a26bf338cdad3643a6e7c3d78a172baadba15c1a"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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