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Date: Mon, 7 Dec 2020 15:05:23 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Daeho Jeong <daeho43@...il.com>, <linux-kernel@...r.kernel.org>,
<linux-f2fs-devel@...ts.sourceforge.net>, <kernel-team@...roid.com>
CC: Jaegeuk Kim <jaegeuk@...nel.org>,
Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: fix race of pending_pages in
decompression
On 2020/12/5 12:26, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@...gle.com>
>
> 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
Is race condition as below?
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
If this is correct, could you please add this into commit message?
>
> Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
> v3: back to v1 and enabled verity in a unit of cluster
> v2: merged verity_pages with pending_pages, and increased the
> pending_pages count only if STEP_VERITY is set on bio
> ---
> fs/f2fs/compress.c | 2 --
> fs/f2fs/data.c | 51 ++++++++++++++++++++++++++++++++++++----------
> fs/f2fs/f2fs.h | 1 +
> 3 files changed, 41 insertions(+), 13 deletions(-)
>
> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
> index 87090da8693d..832b19986caf 100644
> --- a/fs/f2fs/compress.c
> +++ b/fs/f2fs/compress.c
> @@ -803,8 +803,6 @@ 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 42254d3859c7..861e5783a5fc 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 +2248,22 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
> goto out_put_dnode;
> }
>
> + 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))) {
It looks like it will be better to move this into merge condition?
if (bio && (!page_is_mergeable(sbi, bio,
*last_block_in_bio, blkaddr) ||
!f2fs_crypt_mergeable_bio(bio, inode, page->index, NULL) ||
f2fs_verify_mergeable_bio())) {
Thanks,
> + __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 +2279,31 @@ 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 94d16bde5e24..f328f55fb0a0 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1341,6 +1341,7 @@ 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 */
>
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