Re: [PATCH] btrfs: Prevent the use of invalid extent root
From: Qu Wenruo
Date: Wed Jan 01 2025 - 23:43:05 EST
在 2025/1/2 14:35, Lizhi Xu 写道:
syzbot reported a null-ptr-deref in find_first_extent_item. [1]
The btrfs filesystem did not successfully initialize extent root to the
global root tree when mounted, this is because extent buffer is not uptodate,
which causes the failure to read the tree root, which in turn causes extent
root to not be inserted into the global root tree.
Sorry I didn't notice your fix and sent out my version.
I'd prefer your patch to mention that, this is not the common case.
As a btrfs can not be mounted with corrupted extent root.
Such fs can only be mounted with rescue=all,ro mount option as a data
salvage method.
And you do not need to go through all the global root/extent buffer
uptodate things, just mention a corrupted extent tree root is more than
good enough.
To prevent this issue, add extent root check before using it.
[1]
Unable to handle kernel paging request at virtual address dfff800000000041
KASAN: null-ptr-deref in range [0x0000000000000208-0x000000000000020f]
Mem abort info:
ESR = 0x0000000096000005
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x05: level 1 translation fault
Data abort info:
ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[dfff800000000041] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 UID: 0 PID: 6417 Comm: syz-executor153 Not tainted 6.13.0-rc3-syzkaller-g573067a5a685 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : find_first_extent_item+0xac/0x674 fs/btrfs/scrub.c:1375
lr : find_first_extent_item+0xa4/0x674 fs/btrfs/scrub.c:1374
sp : ffff8000a5be6e60
x29: ffff8000a5be6f80 x28: dfff800000000000 x27: 0000000000000000
x26: 0000000000400000 x25: 0000000000400000 x24: 1fffe0001848ab0a
x23: 0000000000000208 x22: ffff8000a5be6f20 x21: ffff0000c2455858
x20: ffff8000a5be6ec0 x19: ffff0000db072010 x18: ffff0000db072010
x17: 000000000000e32c x16: ffff80008b5fea08 x15: 0000000000000004
x14: 1fffe0001b60c031 x13: 0000000000000000 x12: ffff700014b7cdd8
x11: ffff80008257f234 x10: 0000000000ff0100 x9 : 0000000000000000
x8 : 0000000000000041 x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 0000000000000008 x3 : 0000000000400000
x2 : 0000000000100000 x1 : ffff0000db072010 x0 : 0000000000000000
Call trace:
find_first_extent_item+0xac/0x674 fs/btrfs/scrub.c:1375 (P)
scrub_find_fill_first_stripe+0x2c0/0xab8 fs/btrfs/scrub.c:1551
queue_scrub_stripe fs/btrfs/scrub.c:1921 [inline]
scrub_simple_mirror+0x440/0x7e4 fs/btrfs/scrub.c:2152
scrub_stripe+0x7e4/0x2174 fs/btrfs/scrub.c:2317
scrub_chunk+0x268/0x41c fs/btrfs/scrub.c:2443
scrub_enumerate_chunks+0xd38/0x1784 fs/btrfs/scrub.c:2707
btrfs_scrub_dev+0x5a8/0xb34 fs/btrfs/scrub.c:3029
btrfs_ioctl_scrub+0x1f4/0x3e8 fs/btrfs/ioctl.c:3248
btrfs_ioctl+0x6a8/0xb04 fs/btrfs/ioctl.c:5246
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl fs/ioctl.c:892 [inline]
__arm64_sys_ioctl+0x14c/0x1cc fs/ioctl.c:892
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
Reported-by: syzbot+339e9dbe3a2ca419b85d@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=339e9dbe3a2ca419b85d
If you understand the reason why this is possible in the first place,
you can find out the offending commit, where the rescue=ibadroot mount
option is introduced.
Although in the latest kernel it's b979547513ff ("btrfs: scrub:
introduce helper to find and fill sector info for a scrub_stripe")
causing the problem, the same problem also happens before the scrub rework.
So next time please add related fixes: tag for similar reports.
Thanks,
Qu
Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
---
fs/btrfs/scrub.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 204c928beaf9..6080839cec95 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1372,10 +1372,14 @@ static int find_first_extent_item(struct btrfs_root *extent_root,
struct btrfs_path *path,
u64 search_start, u64 search_len)
{
- struct btrfs_fs_info *fs_info = extent_root->fs_info;
+ struct btrfs_fs_info *fs_info;
struct btrfs_key key;
int ret;
+ if (!extent_root)
+ return -ENOENT;
+
+ fs_info = extent_root->fs_info;
/* Continue using the existing path */
if (path->nodes[0])
goto search_forward;