| Message ID | 20170809171016.7501-1-bo.li.liu@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Aug 09, 2017 at 11:10:16AM -0600, Liu Bo wrote: > There is a cornel case that slip through the checkers in functions ^^^^^^ corner Sorry, that's been bugging me every time it goes past. A cornel is a kind of tree, apparently. Hugo. > 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 <fdmanana@suse.com> > Signed-off-by: Liu Bo <bo.li.liu@oracle.com> > --- > > v3: Remove the unnecessary ASSERT and num_pages. > > v2: Improve the commit log to clarify that this can only happen if > metadata is corrupted. > > 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 0aff9b2..e6c6853 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -5417,8 +5417,12 @@ void read_extent_buffer(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); > > @@ -5491,6 +5495,12 @@ 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 +5512,6 @@ 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;
Hugo Mills posted on Wed, 09 Aug 2017 18:15:29 +0000 as excerpted: > On Wed, Aug 09, 2017 at 11:10:16AM -0600, Liu Bo wrote: >> There is a cornel case that slip through the checkers in functions > ^^^^^^ corner > > Sorry, that's been bugging me every time it goes past. A cornel is > a kind of tree, apparently. LOL! Me too but likely more so because I actually live in Cornell Condominiums so seeing "cornel" in this context is a rather confusing context switch, to say the least! I let it slip the first time as I never expected it to make it to a v3, but...
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 0aff9b2..e6c6853 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -5417,8 +5417,12 @@ void read_extent_buffer(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); @@ -5491,6 +5495,12 @@ 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 +5512,6 @@ 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;