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, 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.
Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
---
v2: Improve the commit log to clarify that this can only happen if
metadata is corrupted.
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
--
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