CVE-2024-35949

In the Linux kernel, the following vulnerability has been resolved: btrfs:
make sure that WRITTEN is set on all metadata blocks We previously would
call btrfs_check_leaf() if we had the check integrity code enabled, which
meant that we could only run the extended leaf checks if we had WRITTEN set
on the header flags. This leaves a gap in our checking, because we could
end up with corruption on disk where WRITTEN isn’t set on the leaf, and
then the extended leaf checks don’t get run which we rely on to validate
all of the item pointers to make sure we don’t access memory outside of the
extent buffer. However, since 732fab95abe2 (“btrfs: check-integrity: remove
CONFIG_BTRFS_FS_CHECK_INTEGRITY option”) we no longer call
btrfs_check_leaf() from btrfs_mark_buffer_dirty(), which means we only ever
call it on blocks that are being written out, and thus have WRITTEN set, or
that are being read in, which should have WRITTEN set. Add checks to make
sure we have WRITTEN set appropriately, and then make sure
__btrfs_check_leaf() always does the item checking. This will protect us
from file systems that have been corrupted and no longer have WRITTEN set
on some of the blocks. This was hit on a crafted image tweaking the WRITTEN
bit and reported by KASAN as out-of-bound access in the eb accessors. The
example is a dir item at the end of an eb. [2.042] BTRFS warning (device
loop1): bad eb member start: ptr 0x3fff start 30572544 member offset 16410
size 2 [2.040] general protection fault, probably for non-canonical address
0xe0009d1000000003: 0000 [#1] PREEMPT SMP KASAN NOPTI [2.537] KASAN: maybe
wild-memory-access in range [0x0005088000000018-0x000508800000001f] [2.729]
CPU: 0 PID: 2587 Comm: mount Not tainted 6.8.2 #1 [2.729] Hardware name:
QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 [2.621]
RIP: 0010:btrfs_get_16+0x34b/0x6d0 [2.621] RSP: 0018:ffff88810871fab8
EFLAGS: 00000206 [2.621] RAX: 0000a11000000003 RBX: ffff888104ff8720 RCX:
ffff88811b2288c0 [2.621] RDX: dffffc0000000000 RSI: ffffffff81dd8aca RDI:
ffff88810871f748 [2.621] RBP: 000000000000401a R08: 0000000000000001 R09:
ffffed10210e3ee9 [2.621] R10: ffff88810871f74f R11: 205d323430333737 R12:
000000000000001a [2.621] R13: 000508800000001a R14: 1ffff110210e3f5d R15:
ffffffff850011e8 [2.621] FS: 00007f56ea275840(0000)
GS:ffff88811b200000(0000) knlGS:0000000000000000 [2.621] CS: 0010 DS: 0000
ES: 0000 CR0: 0000000080050033 [2.621] CR2: 00007febd13b75c0 CR3:
000000010bb50000 CR4: 00000000000006f0 [2.621] Call Trace: [2.621] <TASK>
[2.621] ? show_regs+0x74/0x80 [2.621] ? die_addr+0x46/0xc0 [2.621] ?
exc_general_protection+0x161/0x2a0 [2.621] ?
asm_exc_general_protection+0x26/0x30 [2.621] ? btrfs_get_16+0x33a/0x6d0
[2.621] ? btrfs_get_16+0x34b/0x6d0 [2.621] ? btrfs_get_16+0x33a/0x6d0
[2.621] ? __pfx_btrfs_get_16+0x10/0x10 [2.621] ?
__pfx_mutex_unlock+0x10/0x10 [2.621] btrfs_match_dir_item_name+0x101/0x1a0
[2.621] btrfs_lookup_dir_item+0x1f3/0x280 [2.621] ?
__pfx_btrfs_lookup_dir_item+0x10/0x10 [2.621] btrfs_get_tree+0xd25/0x1910 [
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