在 2021/10/1 17:18, Jan Kara 写道:
On Sat 04-09-21 12:49:46, yangerkun wrote:Our stress testing with IO error can trigger follow OOB with a very low probability. [59898.282466] BUG: KASAN: slab-out-of-bounds in ext4_find_extent+0x2e4/0x480 ... [59898.287162] Call Trace: [59898.287575] dump_stack+0x8b/0xb9 [59898.288070] print_address_description+0x73/0x280 [59898.289903] ext4_find_extent+0x2e4/0x480 [59898.290553] ext4_ext_map_blocks+0x125/0x1470 [59898.295481] ext4_map_blocks+0x5ee/0x940 [59898.315984] ext4_mpage_readpages+0x63c/0xdb0 [59898.320231] read_pages+0xe6/0x370 [59898.321589] __do_page_cache_readahead+0x233/0x2a0 [59898.321594] ondemand_readahead+0x157/0x450 [59898.321598] generic_file_read_iter+0xcb2/0x1550 [59898.328828] __vfs_read+0x233/0x360 [59898.328840] vfs_read+0xa5/0x190 [59898.330126] ksys_read+0xa5/0x150 [59898.331405] do_syscall_64+0x6d/0x1f0 [59898.331418] entry_SYSCALL_64_after_hwframe+0x44/0xa9 Digging deep and we found it's actually a xattr block which can happened with follow steps: 1. extent update for file1 and will remove a leaf extent block(block A) 2. we need update the idx extent block too 3. block A has been allocated as a xattr block and will set verified 3. io error happened for this idx block and will the buffer has been released late 4. extent find for file1 will read the idx block and see block A again 5. since the buffer of block A is already verified, we will use it directly, which can lead the upper OOB Same as __ext4_xattr_check_block, we can check magic even the buffer is verified to fix the problem. Signed-off-by: yangerkun <yangerkun@xxxxxxxxxx>Honestly, I'm not sure if this is worth it. What you suggest will work if the magic is overwritten but if we reallocate the block for something else but the magic happens to stay intact, we have a problem. The filesystem is corrupted at that point with metadata blocks being multiply claimed and that's very difficult to deal with. Maybe we should start ignoring buffer_verified() bit once the fs is known to have errors and recheck the buffer contents on each access? Sure it will be slow but I have little sympathy towards people running filesystems with errors... What do people think?
What you means was that something like a extent block for inode A has been reallocate as a extent block for inode B? Ignoring buffer_verified seems useless for this case since extent check will pass. Maybe we should first try to prevent the OOB...
Honza--- fs/ext4/extents.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 8559e288472f..d2e2ae90bc4a 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -506,6 +506,14 @@ __read_extent_tree_block(const char *function, unsigned int line, goto errout; } if (buffer_verified(bh)) { + if (unlikely(ext_block_hdr(bh)->eh_magic != EXT4_EXT_MAGIC)) { + err = -EFSCORRUPTED; + ext4_error_inode(inode, function, line, 0, + "invalid magic for verified extent block %llu", + (unsigned long long)bh->b_blocknr); + goto errout; + } + if (!(flags & EXT4_EX_FORCE_CACHE)) return bh; } else { -- 2.31.1
