When compressed data deduplication is enabled, multiple logical extents
may reference the same compressed physical cluster.
The previous commit 94c43de73521 ("erofs: fix wrong primary bvec
selection on deduplicated extents") already avoids using shortened
bvecs. However, in such cases, the extra temporary buffers also
need to be preserved for later use in z_erofs_fill_other_copies() to
to prevent data corruption.
IOWs, extra temporary buffers have to be retained not only due to
varying start relative offsets (`pageofs_out`, as indicated by
`pcl->multibases`) but also because of shortened bvecs.
android.hardware.graphics.compo...@2.1.so : 270696 bytes
0: 0.. 204185 | 204185 : 628019200.. 628084736 | 65536
-> 1: 204185.. 225536 | 21351 : 544063488.. 544129024 | 65536
2: 225536.. 270696 | 45160 : 0.. 0 | 0
com.android.vndk.v28.apex : 93814897 bytes
...
364: 53869896..54095257 | 225361 : 543997952.. 544063488 | 65536
-> 365: 54095257..54309344 | 214087 : 544063488.. 544129024 | 65536
366: 54309344..54514557 | 205213 : 544129024.. 544194560 | 65536
...
Both 204185 and 54095257 have the same start relative offset of 3481,
but the logical page 55 of `android.hardware.graphics.compo...@2.1.so`
ranges from 225280 to 229632, forming a shortened bvec [225280, 225536)
that cannot be used for decompressing the range from 54095257 to
54309344 of `com.android.vndk.v28.apex`.
Since `pcl->multibases` is already meaningless, just mark `keepxcpy`
on demand for simplicity.
Again, this issue can only lead to data corruption if `-Ededupe` is on.
Fixes: 94c43de73521 ("erofs: fix wrong primary bvec selection on deduplicated
extents")
Signed-off-by: Gao Xiang <hsiang...@linux.alibaba.com>
---
fs/erofs/zdata.c | 31 ++++++++++++++-----------------
1 file changed, 14 insertions(+), 17 deletions(-)
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 5c061aaeeb45..b8e6b76c23d5 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -79,9 +79,6 @@ struct z_erofs_pcluster {
/* L: whether partial decompression or not */
bool partial;
- /* L: indicate several pageofs_outs or not */
- bool multibases;
-
/* L: whether extra buffer allocations are best-effort */
bool besteffort;
@@ -1046,8 +1043,6 @@ static int z_erofs_scan_folio(struct z_erofs_frontend *f,
break;
erofs_onlinefolio_split(folio);
- if (f->pcl->pageofs_out != (map->m_la & ~PAGE_MASK))
- f->pcl->multibases = true;
if (f->pcl->length < offset + end - map->m_la) {
f->pcl->length = offset + end - map->m_la;
f->pcl->pageofs_out = map->m_la & ~PAGE_MASK;
@@ -1093,7 +1088,6 @@ struct z_erofs_backend {
struct page *onstack_pages[Z_EROFS_ONSTACK_PAGES];
struct super_block *sb;
struct z_erofs_pcluster *pcl;
-
/* pages with the longest decompressed length for deduplication */
struct page **decompressed_pages;
/* pages to keep the compressed data */
@@ -1102,6 +1096,8 @@ struct z_erofs_backend {
struct list_head decompressed_secondary_bvecs;
struct page **pagepool;
unsigned int onstack_used, nr_pages;
+ /* indicate if temporary copies should be preserved for later use */
+ bool keepxcpy;
};
struct z_erofs_bvec_item {
@@ -1112,18 +1108,20 @@ struct z_erofs_bvec_item {
static void z_erofs_do_decompressed_bvec(struct z_erofs_backend *be,
struct z_erofs_bvec *bvec)
{
+ int poff = bvec->offset + be->pcl->pageofs_out;
struct z_erofs_bvec_item *item;
- unsigned int pgnr;
-
- if (!((bvec->offset + be->pcl->pageofs_out) & ~PAGE_MASK) &&
- (bvec->end == PAGE_SIZE ||
- bvec->offset + bvec->end == be->pcl->length)) {
- pgnr = (bvec->offset + be->pcl->pageofs_out) >> PAGE_SHIFT;
- DBG_BUGON(pgnr >= be->nr_pages);
- if (!be->decompressed_pages[pgnr]) {
- be->decompressed_pages[pgnr] = bvec->page;
+ struct page **page;
+
+ if (!(poff & ~PAGE_MASK) && (bvec->end == PAGE_SIZE ||
+ bvec->offset + bvec->end == be->pcl->length)) {
+ DBG_BUGON((poff >> PAGE_SHIFT) >= be->nr_pages);
+ page = be->decompressed_pages + (poff >> PAGE_SHIFT);
+ if (!*page) {
+ *page = bvec->page;
return;
}
+ } else {
+ be->keepxcpy = true;
}
/* (cold path) one pcluster is requested multiple times */
@@ -1289,7 +1287,7 @@ static int z_erofs_decompress_pcluster(struct
z_erofs_backend *be, int err)
.alg = pcl->algorithmformat,
.inplace_io = overlapped,
.partial_decoding = pcl->partial,
- .fillgaps = pcl->multibases,
+ .fillgaps = be->keepxcpy,
.gfp = pcl->besteffort ? GFP_KERNEL :
GFP_NOWAIT | __GFP_NORETRY
}, be->pagepool);
@@ -1346,7 +1344,6 @@ static int z_erofs_decompress_pcluster(struct
z_erofs_backend *be, int err)
pcl->length = 0;
pcl->partial = true;
- pcl->multibases = false;
pcl->besteffort = false;
pcl->bvset.nextpage = NULL;
pcl->vcnt = 0;
--
2.43.5
