Messages in this thread | | | Date | Sun, 7 Nov 2010 22:30:39 +0100 (CET) | From | Jesper Juhl <> | Subject | btrfs: potential null derefs |
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Hi,
There are a number of potential NULL pointer dereferences in BTRFS - see below.
Unfortunately I don't know what the best way to deal with these are in BTRFS, so I'll leave the bug fixing to others and stick to just reporting them.
In fs/btrfs/file.c::btrfs_file_aio_write() we do this: ... pages = kmalloc(nrptrs * sizeof(struct page *), GFP_KERNEL); ...[skip lots of lines that don't touch 'pages']... memset(pages, 0, sizeof(struct page *) * nrptrs);
ret = btrfs_delalloc_reserve_space(inode, write_bytes); if (ret) goto out;
ret = prepare_pages(root, file, pages, num_pages, pos, first_index, last_index, write_bytes); ...
since kmalloc() may fail and return a NULL pointer this could potentially go bad.
Also in fs/btrfs/compression.c::btrfs_submit_compressed_write() there's this: ... cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS); atomic_set(&cb->pending_bios, 0); cb->errors = 0; ...
Which will also dereference a NULL pointer when kmalloc() fails.
and in the same function: ... bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS); bio->bi_private = cb; ... bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS); bio->bi_private = cb; ...
Which are also potential NULL derefs since (at least as far as I can tell) compressed_bio_alloc() can also fail and return NULL.
And then in btrfs_submit_compressed_read() : ... cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS); atomic_set(&cb->pending_bios, 0); cb->errors = 0; ... cb->compressed_pages = kmalloc(sizeof(struct page *) * nr_pages, GFP_NOFS); bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
for (page_index = 0; page_index < nr_pages; page_index++) { cb->compressed_pages[page_index] = alloc_page(GFP_NOFS | __GFP_HIGHMEM); } ... comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS); comp_bio->bi_private = cb; ...
All 3 risk dereferencing a NULL pointer when the allocations fail.
Enjoy ;-)
PS. Please CC me on replies.
-- Jesper Juhl <jj@chaosbits.net> http://www.chaosbits.net/ Plain text mails only, please http://www.expita.com/nomime.html Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
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