[PATCH 5.10 47/63] f2fs: fix race of pending_pages in decompression

Greg Kroah-Hartman
2021-01-04T16:05:56Z

From: Daeho Jeong <daehojeong@google.com>

[ Upstream commit 6422a71ef40e4751d59b8c9412e7e2dafe085878 ]

I found out f2fs_free_dic() is invoked in a wrong timing, but
f2fs_verify_bio() still needed the dic info and it triggered the
below kernel panic. It has been caused by the race condition of
pending_pages value between decompression and verity logic, when
the same compression cluster had been split in different bios.
By split bios, f2fs_verify_bio() ended up with decreasing
pending_pages value before it is reset to nr_cpages by
f2fs_decompress_pages() and caused the kernel panic.

[ 4416.564763] Unable to handle kernel NULL pointer dereference
at virtual address 0000000000000000
...
[ 4416.896016] Workqueue: fsverity_read_queue f2fs_verity_work
[ 4416.908515] pc : fsverity_verify_page+0x20/0x78
[ 4416.913721] lr : f2fs_verify_bio+0x11c/0x29c
[ 4416.913722] sp : ffffffc019533cd0
[ 4416.913723] x29: ffffffc019533cd0 x28: 0000000000000402
[ 4416.913724] x27: 0000000000000001 x26: 0000000000000100
[ 4416.913726] x25: 0000000000000001 x24: 0000000000000004
[ 4416.913727] x23: 0000000000001000 x22: 0000000000000000
[ 4416.913728] x21: 0000000000000000 x20: ffffffff2076f9c0
[ 4416.913729] x19: ffffffff2076f9c0 x18: ffffff8a32380c30
[ 4416.913731] x17: ffffffc01f966d97 x16: 0000000000000298
[ 4416.913732] x15: 0000000000000000 x14: 0000000000000000
[ 4416.913733] x13: f074faec89ffffff x12: 0000000000000000
[ 4416.913734] x11: 0000000000001000 x10: 0000000000001000
[ 4416.929176] x9 : ffffffff20d1f5c7 x8 : 0000000000000000
[ 4416.929178] x7 : 626d7464ff286b6b x6 : ffffffc019533ade
[ 4416.929179] x5 : 000000008049000e x4 : ffffffff2793e9e0
[ 4416.929180] x3 : 000000008049000e x2 : ffffff89ecfa74d0
[ 4416.929181] x1 : 0000000000000c40 x0 : ffffffff2076f9c0
[ 4416.929184] Call trace:
[ 4416.929187] fsverity_verify_page+0x20/0x78
[ 4416.929189] f2fs_verify_bio+0x11c/0x29c
[ 4416.929192] f2fs_verity_work+0x58/0x84
[ 4417.050667] process_one_work+0x270/0x47c
[ 4417.055354] worker_thread+0x27c/0x4d8
[ 4417.059784] kthread+0x13c/0x320
[ 4417.063693] ret_from_fork+0x10/0x18

Chao pointed this can happen by the below race condition.

Thread A f2fs_post_read_wq fsverity_wq
- f2fs_read_multi_pages()
- f2fs_alloc_dic
- dic->pending_pages = 2
- submit_bio()
- submit_bio()
- f2fs_post_read_work() handle first bio
- f2fs_decompress_work()
- __read_end_io()
- f2fs_decompress_pages()
- dic->pending_pages--
- enqueue f2fs_verity_work()
- f2fs_verity_work() handle first bio
- f2fs_verify_bio()
- dic->pending_pages--
- f2fs_post_read_work() handle second bio
- f2fs_decompress_work()
- enqueue f2fs_verity_work()
- f2fs_verify_pages()
- f2fs_free_dic()

- f2fs_verity_work() handle second bio
- f2fs_verfy_bio()
- use-after-free on dic

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/f2fs/compress.c | 2 --
fs/f2fs/data.c | 58 +++++++++++++++++++++++++++++++++++++---------
fs/f2fs/f2fs.h | 1 +
3 files changed, 48 insertions(+), 13 deletions(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 14262e0f1cd60..c5fee4d7ea72f 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -798,8 +798,6 @@ void f2fs_decompress_pages(struct bio *bio, struct page *page, bool verity)
if (cops->destroy_decompress_ctx)
cops->destroy_decompress_ctx(dic);
out_free_dic:
- if (verity)
- atomic_set(&dic->pending_pages, dic->nr_cpages);
if (!verity)
f2fs_decompress_end_io(dic->rpages, dic->cluster_size,
ret, false);
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index be4da52604edc..b29243ee1c3e5 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -202,7 +202,7 @@ static void f2fs_verify_bio(struct bio *bio)
dic = (struct decompress_io_ctx *)page_private(page);

if (dic) {
- if (atomic_dec_return(&dic->pending_pages))
+ if (atomic_dec_return(&dic->verity_pages))
continue;
f2fs_verify_pages(dic->rpages,
dic->cluster_size);
@@ -1027,7 +1027,8 @@ static inline bool f2fs_need_verity(const struct inode *inode, pgoff_t idx)

static struct bio *f2fs_grab_read_bio(struct inode *inode, block_t blkaddr,
unsigned nr_pages, unsigned op_flag,
- pgoff_t first_idx, bool for_write)
+ pgoff_t first_idx, bool for_write,
+ bool for_verity)
{
struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
struct bio *bio;
@@ -1049,7 +1050,7 @@ static struct bio *f2fs_grab_read_bio(struct inode *inode, block_t blkaddr,
post_read_steps |= 1 << STEP_DECRYPT;
if (f2fs_compressed_file(inode))
post_read_steps |= 1 << STEP_DECOMPRESS_NOWQ;
- if (f2fs_need_verity(inode, first_idx))
+ if (for_verity && f2fs_need_verity(inode, first_idx))
post_read_steps |= 1 << STEP_VERITY;

if (post_read_steps) {
@@ -1079,7 +1080,7 @@ static int f2fs_submit_page_read(struct inode *inode, struct page *page,
struct bio *bio;

bio = f2fs_grab_read_bio(inode, blkaddr, 1, op_flags,
- page->index, for_write);
+ page->index, for_write, true);
if (IS_ERR(bio))
return PTR_ERR(bio);

@@ -2133,7 +2134,7 @@ static int f2fs_read_single_page(struct inode *inode, struct page *page,
if (bio == NULL) {
bio = f2fs_grab_read_bio(inode, block_nr, nr_pages,
is_readahead ? REQ_RAHEAD : 0, page->index,
- false);
+ false, true);
if (IS_ERR(bio)) {
ret = PTR_ERR(bio);
bio = NULL;
@@ -2180,6 +2181,8 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
const unsigned blkbits = inode->i_blkbits;
const unsigned blocksize = 1 << blkbits;
struct decompress_io_ctx *dic = NULL;
+ struct bio_post_read_ctx *ctx;
+ bool for_verity = false;
int i;
int ret = 0;

@@ -2245,10 +2248,29 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
goto out_put_dnode;
}

+ /*
+ * It's possible to enable fsverity on the fly when handling a cluster,
+ * which requires complicated error handling. Instead of adding more
+ * complexity, let's give a rule where end_io post-processes fsverity
+ * per cluster. In order to do that, we need to submit bio, if previous
+ * bio sets a different post-process policy.
+ */
+ if (fsverity_active(cc->inode)) {
+ atomic_set(&dic->verity_pages, cc->nr_cpages);
+ for_verity = true;
+
+ if (bio) {
+ ctx = bio->bi_private;
+ if (!(ctx->enabled_steps & (1 << STEP_VERITY))) {
+ __submit_bio(sbi, bio, DATA);
+ bio = NULL;
+ }
+ }
+ }
+
for (i = 0; i < dic->nr_cpages; i++) {
struct page *page = dic->cpages[i];
block_t blkaddr;
- struct bio_post_read_ctx *ctx;

blkaddr = data_blkaddr(dn.inode, dn.node_page,
dn.ofs_in_node + i + 1);
@@ -2264,17 +2286,31 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
if (!bio) {
bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
is_readahead ? REQ_RAHEAD : 0,
- page->index, for_write);
+ page->index, for_write, for_verity);
if (IS_ERR(bio)) {
+ unsigned int remained = dic->nr_cpages - i;
+ bool release = false;
+
ret = PTR_ERR(bio);
dic->failed = true;
- if (!atomic_sub_return(dic->nr_cpages - i,
- &dic->pending_pages)) {
+
+ if (for_verity) {
+ if (!atomic_sub_return(remained,
+ &dic->verity_pages))
+ release = true;
+ } else {
+ if (!atomic_sub_return(remained,
+ &dic->pending_pages))
+ release = true;
+ }
+
+ if (release) {
f2fs_decompress_end_io(dic->rpages,
- cc->cluster_size, true,
- false);
+ cc->cluster_size, true,
+ false);
f2fs_free_dic(dic);
}
+
f2fs_put_dnode(&dn);
*bio_ret = NULL;
return ret;
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index e4344d98a780c..06e5a6053f3f9 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1410,6 +1410,7 @@ struct decompress_io_ctx {
size_t rlen; /* valid data length in rbuf */
size_t clen; /* valid data length in cbuf */
atomic_t pending_pages; /* in-flight compressed page count */
+ atomic_t verity_pages; /* in-flight page count for verity */
bool failed; /* indicate IO error during decompression */
void *private; /* payload buffer for specified decompression algorithm */
void *private2; /* extra payload buffer */
--
2.27.0