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f2fs: fix race of pending_pages in decompression

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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>
This commit is contained in:
Daeho Jeong 2020-12-05 13:26:26 +09:00 committed by Jaegeuk Kim
parent 96dd025195
commit 6422a71ef4
3 changed files with 48 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/f2fs/compress.c
View File

@ -821,8 +821,6 @@ destroy_decompress_ctx:
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);

58
fs/f2fs/data.c
View File

@ -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);
@ -1030,7 +1030,8 @@ 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;
@ -1052,7 +1053,7 @@ 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) {
@ -1082,7 +1083,7 @@ 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);
@ -2120,7 +2121,7 @@ submit_and_realloc:
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;
@ -2166,6 +2167,8 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
sector_t last_block_in_file;
const unsigned blocksize = blks_to_bytes(inode, 1);
struct decompress_io_ctx *dic = NULL;
struct bio_post_read_ctx *ctx;
bool for_verity = false;
int i;
int ret = 0;
@ -2231,10 +2234,29 @@ 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);
@ -2250,17 +2272,31 @@ submit_and_realloc:
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;

1
fs/f2fs/f2fs.h
View File

@ -1354,6 +1354,7 @@ 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 */