* [PATCH AUTOSEL 4.9 37/48] btrfs: subpage: check if there are compressed extents inside one page
[not found] <20210909120015.150411-1-sashal@kernel.org>
@ 2021-09-09 12:00 ` Sasha Levin
2021-09-09 13:01 ` David Sterba
2021-09-09 12:00 ` [PATCH AUTOSEL 4.9 38/48] btrfs: subpage: fix race between prepare_pages() and btrfs_releasepage() Sasha Levin
1 sibling, 1 reply; 4+ messages in thread
From: Sasha Levin @ 2021-09-09 12:00 UTC (permalink / raw)
To: linux-kernel, stable; +Cc: Qu Wenruo, David Sterba, Sasha Levin, linux-btrfs
From: Qu Wenruo <wqu@suse.com>
[ Upstream commit 3670e6451bc9c39ab3a46f1da19360219e4319f3 ]
[BUG]
When testing experimental subpage compressed write support, it hits a
NULL pointer dereference inside read path:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000018
pc : __pi_memcmp+0x28/0x1ec
lr : check_data_csum+0xd0/0x274 [btrfs]
Call trace:
__pi_memcmp+0x28/0x1ec
btrfs_verify_data_csum+0xf4/0x244 [btrfs]
end_bio_extent_readpage+0x1d0/0x6b0 [btrfs]
bio_endio+0x15c/0x1dc
end_workqueue_fn+0x44/0x64 [btrfs]
btrfs_work_helper+0x74/0x250 [btrfs]
process_one_work+0x1d4/0x47c
worker_thread+0x180/0x400
kthread+0x11c/0x120
ret_from_fork+0x10/0x30
Code: 54000261 d100044c d343fd8c f8408403 (f8408424)
---[ end trace 9e2c59f33ea40866 ]---
[CAUSE]
When reading two compressed extents inside the same page, like the
following layout, we trigger above crash:
0 32K 64K
|-------|\\\\\\\|
| \- Compressed extent (A)
\--------- Compressed extent (B)
For compressed read, we don't need to populate its io_bio->csum, as we
rely on compressed_bio->csum to verify the compressed data, and then
copy the decompressed to inode pages.
Normally btrfs_verify_data_csum() skip such page by checking and
clearing its PageChecked flag
But since that flag is still for the full page, when endio for inode
page range [0, 32K) gets executed, it clears PageChecked flag for the
full page.
Then when endio for inode page range [32K, 64K) gets executed, since the
page no longer has PageChecked flag, it just continues checking, even
though io_bio->csum is NULL.
[FIX]
Thankfully there are only two users of PageChecked bit:
- Cow fixup
Since subpage has its own way to trace page dirty (dirty_bitmap) and
ordered bit (ordered_bitmap), it should never trigger cow fixup.
- Compressed read
We can distinguish such read by just checking io_bio->csum.
So just check io_bio->csum before doing the verification to avoid such
NULL pointer dereference.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/inode.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b744e7d33d87..1b2c7256c931 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3195,6 +3195,20 @@ static int btrfs_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
return 0;
}
+ /*
+ * For subpage case, above PageChecked is not safe as it's not subpage
+ * compatible.
+ * But for now only cow fixup and compressed read utilize PageChecked
+ * flag, while in this context we can easily use io_bio->csum to
+ * determine if we really need to do csum verification.
+ *
+ * So for now, just exit if io_bio->csum is NULL, as it means it's
+ * compressed read, and its compressed data csum has already been
+ * verified.
+ */
+ if (io_bio->csum == NULL)
+ return 0;
+
if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
return 0;
--
2.30.2
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH AUTOSEL 4.9 38/48] btrfs: subpage: fix race between prepare_pages() and btrfs_releasepage()
[not found] <20210909120015.150411-1-sashal@kernel.org>
2021-09-09 12:00 ` [PATCH AUTOSEL 4.9 37/48] btrfs: subpage: check if there are compressed extents inside one page Sasha Levin
@ 2021-09-09 12:00 ` Sasha Levin
2021-09-09 13:01 ` David Sterba
1 sibling, 1 reply; 4+ messages in thread
From: Sasha Levin @ 2021-09-09 12:00 UTC (permalink / raw)
To: linux-kernel, stable
Cc: Qu Wenruo, Ritesh Harjani, Filipe Manana, David Sterba,
Sasha Levin, linux-btrfs
From: Qu Wenruo <wqu@suse.com>
[ Upstream commit e0467866198f7f536806f39e5d0d91ae8018de08 ]
[BUG]
When running generic/095, there is a high chance to crash with subpage
data RW support:
assertion failed: PagePrivate(page) && page->private
------------[ cut here ]------------
kernel BUG at fs/btrfs/ctree.h:3403!
Internal error: Oops - BUG: 0 [#1] SMP
CPU: 1 PID: 3567 Comm: fio Tainted: 5.12.0-rc7-custom+ #17
Hardware name: Khadas VIM3 (DT)
Call trace:
assertfail.constprop.0+0x28/0x2c [btrfs]
btrfs_subpage_assert+0x80/0xa0 [btrfs]
btrfs_subpage_set_uptodate+0x34/0xec [btrfs]
btrfs_page_clamp_set_uptodate+0x74/0xa4 [btrfs]
btrfs_dirty_pages+0x160/0x270 [btrfs]
btrfs_buffered_write+0x444/0x630 [btrfs]
btrfs_direct_write+0x1cc/0x2d0 [btrfs]
btrfs_file_write_iter+0xc0/0x160 [btrfs]
new_sync_write+0xe8/0x180
vfs_write+0x1b4/0x210
ksys_pwrite64+0x7c/0xc0
__arm64_sys_pwrite64+0x24/0x30
el0_svc_common.constprop.0+0x70/0x140
do_el0_svc+0x28/0x90
el0_svc+0x2c/0x54
el0_sync_handler+0x1a8/0x1ac
el0_sync+0x170/0x180
Code: f0000160 913be042 913c4000 955444bc (d4210000)
---[ end trace 3fdd39f4cccedd68 ]---
[CAUSE]
Although prepare_pages() calls find_or_create_page(), which returns the
page locked, but in later prepare_uptodate_page() calls, we may call
btrfs_readpage() which will unlock the page before it returns.
This leaves a window where btrfs_releasepage() can sneak in and release
the page, clearing page->private and causing above ASSERT().
[FIX]
In prepare_uptodate_page(), we should not only check page->mapping, but
also PagePrivate() to ensure we are still holding the correct page which
has proper fs context setup.
Reported-by: Ritesh Harjani <riteshh@linux.ibm.com>
Tested-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/file.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 79454ea77153..c1005833c5a2 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1332,7 +1332,18 @@ static int prepare_uptodate_page(struct inode *inode,
unlock_page(page);
return -EIO;
}
- if (page->mapping != inode->i_mapping) {
+
+ /*
+ * Since btrfs_readpage() will unlock the page before it
+ * returns, there is a window where btrfs_releasepage() can
+ * be called to release the page.
+ * Here we check both inode mapping and PagePrivate() to
+ * make sure the page was not released.
+ *
+ * The private flag check is essential for subpage as we need
+ * to store extra bitmap using page->private.
+ */
+ if (page->mapping != inode->i_mapping || !PagePrivate(page)) {
unlock_page(page);
return -EAGAIN;
}
--
2.30.2
^ permalink raw reply related [flat|nested] 4+ messages in thread