From: Filipe Manana Date: Mon, 29 Jun 2026 14:47:34 +0000 (+0100) Subject: btrfs: fix NULL pointer deref during assertion in btrfs_backref_free_node() X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=f0c1f14cc103a28ba80b3e48b88f23026709db3a;p=thirdparty%2Fkernel%2Flinux.git btrfs: fix NULL pointer deref during assertion in btrfs_backref_free_node() In btrfs_backref_free_node() we have the following assertion: ASSERT(node->eb == NULL, "node->eb->start=%llu", node->eb->start); and a user reported the following crash: Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] CPU: 0 UID: 0 PID: 10422 Comm: syz.0.17 Not tainted 7.1.0-02765-g6b5a2b7d9bc1-dirty #44 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:btrfs_backref_free_node fs/btrfs/backref.c:3057 [inline] RIP: 0010:btrfs_backref_free_node+0xb9/0x200 fs/btrfs/backref.c:3051 Code: 00 fc ff (...) RSP: 0018:ffa0000006b0f3c0 EFLAGS: 00010246 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff840eb78b RDX: 0000000000000000 RSI: ffffffff840eafa5 RDI: ff110000742ab768 RBP: ff110000742ab700 R08: 0000000000000000 R09: 0000000000000000 R10: ff110000742ab700 R11: 00000000000a81f9 R12: ff11000107a92020 R13: ff1100005c182ea8 R14: 0000000000000000 R15: dffffc0000000000 FS: 0000555575536500(0000) GS:ff11000183985000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa3d0e9d580 CR3: 000000002232a000 CR4: 0000000000753ef0 PKRU: 00000000 Call Trace: btrfs_backref_cleanup_node+0x27/0x30 fs/btrfs/backref.c:3133 relocate_tree_block fs/btrfs/relocation.c:2604 [inline] relocate_tree_blocks+0x11b0/0x1a20 fs/btrfs/relocation.c:2707 relocate_block_group+0x499/0xf30 fs/btrfs/relocation.c:3635 do_nonremap_reloc fs/btrfs/relocation.c:5323 [inline] btrfs_relocate_block_group+0x1749/0x5fb0 fs/btrfs/relocation.c:5490 btrfs_relocate_chunk+0x12b/0x950 fs/btrfs/volumes.c:3647 __btrfs_balance fs/btrfs/volumes.c:4586 [inline] btrfs_balance+0x1c7f/0x55c0 fs/btrfs/volumes.c:4973 btrfs_ioctl_balance fs/btrfs/ioctl.c:3474 [inline] btrfs_ioctl+0x38a4/0x5d20 fs/btrfs/ioctl.c:5570 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x11f/0x860 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fb38e3b56dd Code: 02 b8 ff (...) RSP: 002b:00007fff04115788 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007fb38f6b0020 RCX: 00007fb38e3b56dd RDX: 00002000000003c0 RSI: 00000000c4009420 RDI: 0000000000000004 RBP: 00007fb38e451b48 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007fb38f6b0020 R15: 00007fb38f6b002c It seems that this happens on some systems for some reason, when the ASSERT() macro calls the inline function verify_assert_printk_format() to evaluate the format string and arguments, causing the NULL pointer dereference on node->eb. So change the assertion to check for a NULL node->eb before dereferencing it. Also, while at it, make the assertion more useful by printing the owner of the extent buffer as well as its level. Reported-by: Yue Sun Link: https://lore.kernel.org/linux-btrfs/20260626065542.38413-1-samsun1006219@gmail.com/ Fixes: c4e7778580d6 ("btrfs: use verbose assertions in backref.c") Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba --- diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c index 23c3eeb58dc1..1be632c742bd 100644 --- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -3054,7 +3054,10 @@ void btrfs_backref_free_node(struct btrfs_backref_cache *cache, if (node) { ASSERT(list_empty(&node->list)); ASSERT(list_empty(&node->lower)); - ASSERT(node->eb == NULL, "node->eb->start=%llu", node->eb->start); + ASSERT(node->eb == NULL, "node->eb->start=%llu level=%d owner=%llu", + node->eb ? node->eb->start : 0, + node->eb ? btrfs_header_level(node->eb) : 0, + node->eb ? btrfs_header_owner(node->eb) : 0); cache->nr_nodes--; btrfs_put_root(node->root); kfree(node);