Commit 3387206f authored Apr 11, 2011 by Sergei Trofimovich Committed by Chris Mason Apr 11, 2011

btrfs: properly handle overlapping areas in memmove_extent_buffer

Fix data corruption caused by memcpy() usage on overlapping data.
I've observed it first when found out usermode linux crash on btrfs.

?all chain is the following:
------------[ cut here ]------------
WARNING: at /home/slyfox/linux-2.6/fs/btrfs/extent_io.c:3900 memcpy_extent_buffer+0x1a5/0x219()
Call Trace:
6fa39a58:  [<601b495e>] _raw_spin_unlock_irqrestore+0x18/0x1c
6fa39a68:  [<60029ad9>] warn_slowpath_common+0x59/0x70
6fa39aa8:  [<60029b05>] warn_slowpath_null+0x15/0x17
6fa39ab8:  [<600efc97>] memcpy_extent_buffer+0x1a5/0x219
6fa39b48:  [<600efd9f>] memmove_extent_buffer+0x94/0x208
6fa39bc8:  [<600becbf>] btrfs_del_items+0x214/0x473
6fa39c78:  [<600ce1b0>] btrfs_delete_one_dir_name+0x7c/0xda
6fa39cc8:  [<600dad6b>] __btrfs_unlink_inode+0xad/0x25d
6fa39d08:  [<600d7864>] btrfs_start_transaction+0xe/0x10
6fa39d48:  [<600dc9ff>] btrfs_unlink_inode+0x1b/0x3b
6fa39d78:  [<600e04bc>] btrfs_unlink+0x70/0xef
6fa39dc8:  [<6007f0d0>] vfs_unlink+0x58/0xa3
6fa39df8:  [<60080278>] do_unlinkat+0xd4/0x162
6fa39e48:  [<600517db>] call_rcu_sched+0xe/0x10
6fa39e58:  [<600452a8>] __put_cred+0x58/0x5a
6fa39e78:  [<6007446c>] sys_faccessat+0x154/0x166
6fa39ed8:  [<60080317>] sys_unlink+0x11/0x13
6fa39ee8:  [<60016b80>] handle_syscall+0x58/0x70
6fa39f08:  [<60021377>] userspace+0x2d4/0x381
6fa39fc8:  [<60014507>] fork_handler+0x62/0x69
---[ end trace 70b0ca2ef0266b93 ]---

http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg09302.html



Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Reviewed-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

parent 8fb27640

fs/btrfs/extent_io.c

+11 −3

Original line number	Diff line number	Diff line
		@@ -3885,6 +3885,12 @@ static void move_pages(struct page dst_page, struct page src_page,
		kunmap_atomic(dst_kaddr, KM_USER0);
		}

		static inline bool areas_overlap(unsigned long src, unsigned long dst, unsigned long len)
		{
		unsigned long distance = (src > dst) ? src - dst : dst - src;
		return distance < len;
		}

		static void copy_pages(struct page dst_page, struct page src_page,
		unsigned long dst_off, unsigned long src_off,
		unsigned long len)
		@@ -3892,10 +3898,12 @@ static void copy_pages(struct page dst_page, struct page src_page,
		char *dst_kaddr = kmap_atomic(dst_page, KM_USER0);
		char *src_kaddr;

		if (dst_page != src_page)
		if (dst_page != src_page) {
		src_kaddr = kmap_atomic(src_page, KM_USER1);
		else
		} else {
		src_kaddr = dst_kaddr;
		BUG_ON(areas_overlap(src_off, dst_off, len));
		}

		memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
		kunmap_atomic(dst_kaddr, KM_USER0);
		@@ -3970,7 +3978,7 @@ void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
		"len %lu len %lu\n", dst_offset, len, dst->len);
		BUG_ON(1);
		}
		if (dst_offset < src_offset) {
		if (!areas_overlap(src_offset, dst_offset, len)) {
		memcpy_extent_buffer(dst, dst_offset, src_offset, len);
		return;
		}