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author | Qu Wenruo <wqu@suse.com> | 2020-08-04 15:25:47 +0800 |
---|---|---|
committer | David Sterba <dsterba@suse.com> | 2021-04-19 21:32:45 +0200 |
commit | 1d8ba9e7e785b6625f4d8e978e8a284b144a7077 (patch) | |
tree | 579c2d6a6aa361309241c38ac307c57be6fd6539 /fs/btrfs | |
parent | 1d68128c107a0b8c0c9125cb05d4771ddc438369 (diff) | |
download | linux-1d8ba9e7e785b6625f4d8e978e8a284b144a7077.tar.gz linux-1d8ba9e7e785b6625f4d8e978e8a284b144a7077.tar.bz2 linux-1d8ba9e7e785b6625f4d8e978e8a284b144a7077.zip |
btrfs: handle remount to no compress during compression
[BUG]
When running btrfs/071 with inode_need_compress() removed from
compress_file_range(), we got the following crash:
BUG: kernel NULL pointer dereference, address: 0000000000000018
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
Workqueue: btrfs-delalloc btrfs_work_helper [btrfs]
RIP: 0010:compress_file_range+0x476/0x7b0 [btrfs]
Call Trace:
? submit_compressed_extents+0x450/0x450 [btrfs]
async_cow_start+0x16/0x40 [btrfs]
btrfs_work_helper+0xf2/0x3e0 [btrfs]
process_one_work+0x278/0x5e0
worker_thread+0x55/0x400
? process_one_work+0x5e0/0x5e0
kthread+0x168/0x190
? kthread_create_worker_on_cpu+0x70/0x70
ret_from_fork+0x22/0x30
---[ end trace 65faf4eae941fa7d ]---
This is already after the patch "btrfs: inode: fix NULL pointer
dereference if inode doesn't need compression."
[CAUSE]
@pages is firstly created by kcalloc() in compress_file_extent():
pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
Then passed to btrfs_compress_pages() to be utilized there:
ret = btrfs_compress_pages(...
pages,
&nr_pages,
...);
btrfs_compress_pages() will initialize each page as output, in
zlib_compress_pages() we have:
pages[nr_pages] = out_page;
nr_pages++;
Normally this is completely fine, but there is a special case which
is in btrfs_compress_pages() itself:
switch (type) {
default:
return -E2BIG;
}
In this case, we didn't modify @pages nor @out_pages, leaving them
untouched, then when we cleanup pages, the we can hit NULL pointer
dereference again:
if (pages) {
for (i = 0; i < nr_pages; i++) {
WARN_ON(pages[i]->mapping);
put_page(pages[i]);
}
...
}
Since pages[i] are all initialized to zero, and btrfs_compress_pages()
doesn't change them at all, accessing pages[i]->mapping would lead to
NULL pointer dereference.
This is not possible for current kernel, as we check
inode_need_compress() before doing pages allocation.
But if we're going to remove that inode_need_compress() in
compress_file_extent(), then it's going to be a problem.
[FIX]
When btrfs_compress_pages() hits its default case, modify @out_pages to
0 to prevent such problem from happening.
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212331
CC: stable@vger.kernel.org # 5.10+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs')
-rw-r--r-- | fs/btrfs/compression.c | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c index 2600703fab83..17f93fd28f7e 100644 --- a/fs/btrfs/compression.c +++ b/fs/btrfs/compression.c @@ -80,10 +80,15 @@ static int compression_compress_pages(int type, struct list_head *ws, case BTRFS_COMPRESS_NONE: default: /* - * This can't happen, the type is validated several times - * before we get here. As a sane fallback, return what the - * callers will understand as 'no compression happened'. + * This can happen when compression races with remount setting + * it to 'no compress', while caller doesn't call + * inode_need_compress() to check if we really need to + * compress. + * + * Not a big deal, just need to inform caller that we + * haven't allocated any pages yet. */ + *out_pages = 0; return -E2BIG; } } |