There is a cornel case that slip 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. This is adding proper checks in order to avoid invalid memory access, ie. 'general protection', before it's too late. Signed-off-by: Liu Bo <bo.li....@oracle.com> --- fs/btrfs/extent_io.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 0aff9b2..d198e87 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -5416,13 +5416,19 @@ void read_extent_buffer(struct extent_buffer *eb, void *dstv, char *dst = (char *)dstv; size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1); unsigned long i = (start_offset + start) >> PAGE_SHIFT; + unsigned long num_pages = num_extent_pages(eb->start, eb->len); - 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); while (len > 0) { + ASSERT(i < num_pages); page = eb->pages[i]; cur = min(len, (PAGE_SIZE - offset)); @@ -5491,6 +5497,12 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start, 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; @@ -5502,12 +5514,6 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start, *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; -- 2.9.4 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html