6.6-stable review patch. If anyone has any objections, please let me know.
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From: Qu Wenruo wqu@suse.com
commit 10d9d8c3512f16cad47b2ff81ec6fc4b27d8ee10 upstream.
[BUG] There is an internal report that KASAN is reporting use-after-free, with the following backtrace:
BUG: KASAN: slab-use-after-free in btrfs_check_read_bio+0xa68/0xb70 [btrfs] Read of size 4 at addr ffff8881117cec28 by task kworker/u16:2/45 CPU: 1 UID: 0 PID: 45 Comm: kworker/u16:2 Not tainted 6.11.0-rc2-next-20240805-default+ #76 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-3-gd478f380-rebuilt.opensuse.org 04/01/2014 Workqueue: btrfs-endio btrfs_end_bio_work [btrfs] Call Trace: dump_stack_lvl+0x61/0x80 print_address_description.constprop.0+0x5e/0x2f0 print_report+0x118/0x216 kasan_report+0x11d/0x1f0 btrfs_check_read_bio+0xa68/0xb70 [btrfs] process_one_work+0xce0/0x12a0 worker_thread+0x717/0x1250 kthread+0x2e3/0x3c0 ret_from_fork+0x2d/0x70 ret_from_fork_asm+0x11/0x20
Allocated by task 20917: kasan_save_stack+0x37/0x60 kasan_save_track+0x10/0x30 __kasan_slab_alloc+0x7d/0x80 kmem_cache_alloc_noprof+0x16e/0x3e0 mempool_alloc_noprof+0x12e/0x310 bio_alloc_bioset+0x3f0/0x7a0 btrfs_bio_alloc+0x2e/0x50 [btrfs] submit_extent_page+0x4d1/0xdb0 [btrfs] btrfs_do_readpage+0x8b4/0x12a0 [btrfs] btrfs_readahead+0x29a/0x430 [btrfs] read_pages+0x1a7/0xc60 page_cache_ra_unbounded+0x2ad/0x560 filemap_get_pages+0x629/0xa20 filemap_read+0x335/0xbf0 vfs_read+0x790/0xcb0 ksys_read+0xfd/0x1d0 do_syscall_64+0x6d/0x140 entry_SYSCALL_64_after_hwframe+0x4b/0x53
Freed by task 20917: kasan_save_stack+0x37/0x60 kasan_save_track+0x10/0x30 kasan_save_free_info+0x37/0x50 __kasan_slab_free+0x4b/0x60 kmem_cache_free+0x214/0x5d0 bio_free+0xed/0x180 end_bbio_data_read+0x1cc/0x580 [btrfs] btrfs_submit_chunk+0x98d/0x1880 [btrfs] btrfs_submit_bio+0x33/0x70 [btrfs] submit_one_bio+0xd4/0x130 [btrfs] submit_extent_page+0x3ea/0xdb0 [btrfs] btrfs_do_readpage+0x8b4/0x12a0 [btrfs] btrfs_readahead+0x29a/0x430 [btrfs] read_pages+0x1a7/0xc60 page_cache_ra_unbounded+0x2ad/0x560 filemap_get_pages+0x629/0xa20 filemap_read+0x335/0xbf0 vfs_read+0x790/0xcb0 ksys_read+0xfd/0x1d0 do_syscall_64+0x6d/0x140 entry_SYSCALL_64_after_hwframe+0x4b/0x53
[CAUSE] Although I cannot reproduce the error, the report itself is good enough to pin down the cause.
The call trace is the regular endio workqueue context, but the free-by-task trace is showing that during btrfs_submit_chunk() we already hit a critical error, and is calling btrfs_bio_end_io() to error out. And the original endio function called bio_put() to free the whole bio.
This means a double freeing thus causing use-after-free, e.g.:
1. Enter btrfs_submit_bio() with a read bio The read bio length is 128K, crossing two 64K stripes.
2. The first run of btrfs_submit_chunk()
2.1 Call btrfs_map_block(), which returns 64K 2.2 Call btrfs_split_bio() Now there are two bios, one referring to the first 64K, the other referring to the second 64K. 2.3 The first half is submitted.
3. The second run of btrfs_submit_chunk()
3.1 Call btrfs_map_block(), which by somehow failed Now we call btrfs_bio_end_io() to handle the error
3.2 btrfs_bio_end_io() calls the original endio function Which is end_bbio_data_read(), and it calls bio_put() for the original bio.
Now the original bio is freed.
4. The submitted first 64K bio finished Now we call into btrfs_check_read_bio() and tries to advance the bio iter. But since the original bio (thus its iter) is already freed, we trigger the above use-after free.
And even if the memory is not poisoned/corrupted, we will later call the original endio function, causing a double freeing.
[FIX] Instead of calling btrfs_bio_end_io(), call btrfs_orig_bbio_end_io(), which has the extra check on split bios and do the proper refcounting for cloned bios.
Furthermore there is already one extra btrfs_cleanup_bio() call, but that is duplicated to btrfs_orig_bbio_end_io() call, so remove that label completely.
Reported-by: David Sterba dsterba@suse.com Fixes: 852eee62d31a ("btrfs: allow btrfs_submit_bio to split bios") CC: stable@vger.kernel.org # 6.6+ 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/bio.c | 26 ++++++++++++++++++-------- 1 file changed, 18 insertions(+), 8 deletions(-)
--- a/fs/btrfs/bio.c +++ b/fs/btrfs/bio.c @@ -646,7 +646,6 @@ static bool btrfs_submit_chunk(struct bt { struct btrfs_inode *inode = bbio->inode; struct btrfs_fs_info *fs_info = bbio->fs_info; - struct btrfs_bio *orig_bbio = bbio; struct bio *bio = &bbio->bio; u64 logical = bio->bi_iter.bi_sector << SECTOR_SHIFT; u64 length = bio->bi_iter.bi_size; @@ -682,7 +681,7 @@ static bool btrfs_submit_chunk(struct bt bbio->saved_iter = bio->bi_iter; ret = btrfs_lookup_bio_sums(bbio); if (ret) - goto fail_put_bio; + goto fail; }
if (btrfs_op(bio) == BTRFS_MAP_WRITE) { @@ -704,13 +703,13 @@ static bool btrfs_submit_chunk(struct bt
ret = btrfs_bio_csum(bbio); if (ret) - goto fail_put_bio; + goto fail; } else if (use_append || (btrfs_is_zoned(fs_info) && inode && inode->flags & BTRFS_INODE_NODATASUM)) { ret = btrfs_alloc_dummy_sum(bbio); if (ret) - goto fail_put_bio; + goto fail; } }
@@ -718,12 +717,23 @@ static bool btrfs_submit_chunk(struct bt done: return map_length == length;
-fail_put_bio: - if (map_length < length) - btrfs_cleanup_bio(bbio); fail: btrfs_bio_counter_dec(fs_info); - btrfs_bio_end_io(orig_bbio, ret); + /* + * We have split the original bbio, now we have to end both the current + * @bbio and remaining one, as the remaining one will never be submitted. + */ + if (map_length < length) { + struct btrfs_bio *remaining = bbio->private; + + ASSERT(bbio->bio.bi_pool == &btrfs_clone_bioset); + ASSERT(remaining); + + remaining->bio.bi_status = ret; + btrfs_orig_bbio_end_io(remaining); + } + bbio->bio.bi_status = ret; + btrfs_orig_bbio_end_io(bbio); /* Do not submit another chunk */ return true; }