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(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 959E713354; Thu, 8 Oct 2026 22:14:03 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id oyywBqYVyGrLMQAAD6G6ig:T4 (envelope-from ); Thu, 08 Oct 2026 22:14:03 +0000 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Cc: Yalagada Pavan Kumar , syzbot+947286c775f432b073a8@syzkaller.appspotmail.com Subject: [PATCH v4 3/3] btrfs: fix use-after-free on quota enable allocation failure Date: Fri, 9 Oct 2026 08:43:40 +1030 Message-ID: X-Mailer: git-send-email 2.55.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Pre-Result: action=no action; module=Unknown lua; unknown reason X-Spam-Flag: NO X-Spam-Level: X-Rspamd-Pre-Result: action=no action; module=Unknown lua; unknown reason X-Spamd-Result: default: False [0.00 / 50.00]; TAGGED_RCPT(0.00)[947286c775f432b073a8] X-Spam-Score: 0.00 From: Yalagada Pavan Kumar [BUG] There is a syzbot report that a use-after-free bug is triggered after a failed btrfs_quota_enable(): loop0: detected capacity change from 32768 to 0 ================================================================== BUG: KASAN: slab-use-after-free in __list_add_valid_or_report+0x4e/0x130 lib/list_debug.c:29 Read of size 8 at addr ffff888040e0a528 by task syz.0.0/5324 CPU: 0 UID: 0 PID: 5324 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_address_description+0x55/0x1e0 mm/kasan/report.c:378 print_report+0x58/0x70 mm/kasan/report.c:482 kasan_report+0x117/0x150 mm/kasan/report.c:595 __list_add_valid_or_report+0x4e/0x130 lib/list_debug.c:29 __list_add_valid include/linux/list.h:104 [inline] __list_add include/linux/list.h:169 [inline] list_add include/linux/list.h:192 [inline] list_move include/linux/list.h:345 [inline] add_root_to_dirty_list+0x38b/0x470 fs/btrfs/ctree.c:232 btrfs_force_cow_block+0xf09/0x1bf0 fs/btrfs/ctree.c:553 btrfs_cow_block+0x3f1/0xaf0 fs/btrfs/ctree.c:696 btrfs_search_slot+0xd70/0x2d20 fs/btrfs/ctree.c:-1 btrfs_search_prev_slot fs/btrfs/free-space-tree.c:134 [inline] remove_free_space_extent fs/btrfs/free-space-tree.c:732 [inline] __btrfs_remove_from_free_space_tree fs/btrfs/free-space-tree.c:837 [inline] btrfs_remove_from_free_space_tree+0x4d6/0xda0 fs/btrfs/free-space-tree.c:866 alloc_reserved_extent+0x4a/0x2b0 fs/btrfs/extent-tree.c:4976 alloc_reserved_tree_block fs/btrfs/extent-tree.c:5155 [inline] run_delayed_tree_ref fs/btrfs/extent-tree.c:1815 [inline] run_one_delayed_ref fs/btrfs/extent-tree.c:1851 [inline] btrfs_run_delayed_refs_for_head fs/btrfs/extent-tree.c:2058 [inline] __btrfs_run_delayed_refs+0x18b5/0x43b0 fs/btrfs/extent-tree.c:2134 btrfs_run_delayed_refs+0xdc/0x2a0 fs/btrfs/extent-tree.c:2246 btrfs_commit_transaction+0x28a/0x3170 fs/btrfs/transaction.c:2267 sync_filesystem+0x1d2/0x240 fs/sync.c:66 btrfs_reconfigure+0x2dc/0x2100 fs/btrfs/super.c:1511 reconfigure_super+0x232/0x8f0 fs/super.c:1128 do_remount fs/namespace.c:3410 [inline] path_mount+0xd4e/0x1050 fs/namespace.c:4160 do_mount fs/namespace.c:4181 [inline] __do_sys_mount fs/namespace.c:4397 [inline] __se_sys_mount+0x31d/0x420 fs/namespace.c:4374 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f9c8dd9f3ca Allocated by task 5323: kasan_save_stack mm/kasan/common.c:57 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:78 poison_kmalloc_redzone mm/kasan/common.c:409 [inline] __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:426 kasan_kmalloc include/linux/kasan.h:263 [inline] __kmalloc_cache_noprof+0x321/0x600 mm/slub.c:5563 _kmalloc_noprof include/linux/slab.h:991 [inline] _kzalloc_noprof include/linux/slab.h:1312 [inline] btrfs_alloc_root+0x75/0x840 fs/btrfs/disk-io.c:638 btrfs_create_tree+0xa8/0x5c0 fs/btrfs/disk-io.c:832 btrfs_quota_enable+0x3d6/0x1e20 fs/btrfs/qgroup.c:1074 btrfs_ioctl_quota_ctl+0x186/0x1f0 fs/btrfs/ioctl.c:3581 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task 5323: kasan_save_stack mm/kasan/common.c:57 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:78 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584 poison_slab_object mm/kasan/common.c:264 [inline] __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:296 kasan_slab_free include/linux/kasan.h:235 [inline] slab_free_hook mm/slub.c:2748 [inline] slab_free mm/slub.c:6508 [inline] kfree+0x1c5/0x650 mm/slub.c:6801 btrfs_quota_enable+0x1208/0x1e20 fs/btrfs/qgroup.c:1292 btrfs_ioctl_quota_ctl+0x186/0x1f0 fs/btrfs/ioctl.c:3581 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f [CAUSE] During btrfs_quota_enable(), a temporary quota_root is created, then qgroup items are created for each subvolume and inserted into that root. If there are enough subvolumes, the level of quota_root will be bumped, and add_root_to_dirty_list() will be called, adding quota_root->dirty_list into fs_info->dirty_cowonly_roots. But if a problem is hit during btrfs_quota_enable() later, that quota_root will be released through btrfs_put_root(), causing the whole quota_root structure to be released, while leaving fs_info->dirty_cowonly_roots still pointing to the released quota_root->dirty_list. Later access through fs_info->dirty_cowonly_roots will trigger a use-after-free bug. [FIX] With previous patches doing the preparation work: - Always hold the trans_lock when modifying btrfs_root::dirty_list - Unlink all btrfs_root::dirty_list entries from btrfs_transaction::switch_commits when a transaction is cleaned up Now we can just call list_del_init(&root->dirty_list) when btrfs_quota_enable() failed. Also to follow the existing error handling behavior, abort the transaction when the memory preallocation failed. Reported-by: syzbot+947286c775f432b073a8@syzkaller.appspotmail.com Link: https://lore.kernel.org/linux-btrfs/6ac5a5e1.9ad129c8.3ce5b3.0010.GAE@google.com/ Closes: https://syzkaller.appspot.com/bug?extid=947286c775f432b073a8 Signed-off-by: Yalagada Pavan Kumar Reviewed-by: Qu Wenruo [ Change the commit message to include a proper analysis. ] Signed-off-by: Qu Wenruo --- fs/btrfs/qgroup.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index cf8dfd5c692b..a0651fbfe778 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1207,6 +1207,7 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info, prealloc = kzalloc_obj(*prealloc, GFP_NOFS); if (!prealloc) { ret = -ENOMEM; + btrfs_abort_transaction(trans, ret); goto out; } qgroup = add_qgroup_rb(fs_info, prealloc, BTRFS_FS_TREE_OBJECTID); @@ -1296,6 +1297,12 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info, * sysfs entries. */ btrfs_free_qgroup_config(fs_info); + + if (quota_root) { + spin_lock(&fs_info->trans_lock); + list_del_init("a_root->dirty_list); + spin_unlock(&fs_info->trans_lock); + } btrfs_put_root(quota_root); } mutex_unlock(&fs_info->qgroup_ioctl_lock); -- 2.55.0