From f716abd55d1e141772fd44a99c07c89f4aff1978 Mon Sep 17 00:00:00 2001 From: Liu Bo Date: Wed, 9 Aug 2017 11:10:16 -0600 Subject: [PATCH] Btrfs: fix out of bounds array access while reading extent buffer There is a corner case that slips through the checkers in functions reading extent buffer, ie. if (start < eb->len) and (start + len > eb->len), then a) map_private_extent_buffer() returns immediately because it's thinking the range spans across two pages, b) and the checkers in read_extent_buffer(), WARN_ON(start > eb->len) and WARN_ON(start + len > eb->start + eb->len), both are OK in this corner case, but it'd actually try to access the eb->pages out of bounds because of (start + len > eb->len). The case is found by switching extent inline ref type from shared data ref to non-shared data ref, which is a kind of metadata corruption. It'd use the wrong helper to access the eb, eg. btrfs_extent_data_ref_root(eb, ref) is used but the %ref passing here is "struct btrfs_shared_data_ref". And if the extent item happens to be the first item in the eb, then offset/length will get over eb->len which ends up an invalid memory access. This is adding proper checks in order to avoid invalid memory access, ie. 'general protection fault', before it's too late. Reviewed-by: Filipe Manana Signed-off-by: Liu Bo Signed-off-by: Chris Mason Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index ea4947c97505..d17783d70228 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -5404,8 +5404,12 @@ void read_extent_buffer(const struct extent_buffer *eb, void *dstv, size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1); unsigned long i = (start_offset + start) >> PAGE_SHIFT; - WARN_ON(start > eb->len); - WARN_ON(start + len > eb->start + eb->len); + if (start + len > eb->len) { + WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, wanted %lu %lu\n", + eb->start, eb->len, start, len); + memset(dst, 0, len); + return; + } offset = (start_offset + start) & (PAGE_SIZE - 1); @@ -5478,6 +5482,12 @@ int map_private_extent_buffer(const struct extent_buffer *eb, unsigned long end_i = (start_offset + start + min_len - 1) >> PAGE_SHIFT; + if (start + min_len > eb->len) { + WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, wanted %lu %lu\n", + eb->start, eb->len, start, min_len); + return -EINVAL; + } + if (i != end_i) return 1; @@ -5489,12 +5499,6 @@ int map_private_extent_buffer(const struct extent_buffer *eb, *map_start = ((u64)i << PAGE_SHIFT) - start_offset; } - if (start + min_len > eb->len) { - WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, wanted %lu %lu\n", - eb->start, eb->len, start, min_len); - return -EINVAL; - } - p = eb->pages[i]; kaddr = page_address(p); *map = kaddr + offset; -- 2.45.2