On Mon, Aug 7, 2017 at 8:39 PM, Liu Bo <bo.li....@oracle.com> wrote: > 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.
Hi Bo, I don't understand these 2 last paragraphs. How do you fix the invalid memory access? All the change does is make sure that attempts to read from invalid regions of an extent buffer result in a warning and returning an error code. Those paragraphs give the idea that the problem is that some caller is passing a wrong offset/length pair, however you aren't fixing any caller. can you clarify? Also when you say " The case is found by switching extent inline ref type from shared data ref to non-shared data ref", it gives the idea this is a deterministic problem that always happens when doing that switch. If so, can we have a test case? Also missing the word "fault" after 'general protection'. Thanks. > > 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 -- Filipe David Manana, “Whether you think you can, or you think you can't — you're right.” -- 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