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Subject[PATCH] f2fs: fix use-after-free of dicard command entry
Date
As Dan Carpenter reported:

The patch 20ee4382322c: "f2fs: issue small discard by LBA order" from
Jul 8, 2018, leads to the following Smatch warning:

fs/f2fs/segment.c:1277 __issue_discard_cmd_orderly()
warn: 'dc' was already freed.

See also:
fs/f2fs/segment.c:2550 __issue_discard_cmd_range() warn: 'dc' was already freed.

In order to fix this issue, let's get error from __submit_discard_cmd(),
and release current discard command after we referenced next one.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
fs/f2fs/segment.c | 79 +++++++++++++++++++++++++++--------------------
1 file changed, 45 insertions(+), 34 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index be1bf38400ca..8826ea683804 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -998,7 +998,7 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
struct block_device *bdev, block_t lstart,
block_t start, block_t len);
/* this function is copied from blkdev_issue_discard from block/blk-lib.c */
-static void __submit_discard_cmd(struct f2fs_sb_info *sbi,
+static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
struct discard_policy *dpolicy,
struct discard_cmd *dc,
unsigned int *issued)
@@ -1015,10 +1015,10 @@ static void __submit_discard_cmd(struct f2fs_sb_info *sbi,
int err = 0;

if (dc->state != D_PREP)
- return;
+ return 0;

if (is_sbi_flag_set(sbi, SBI_NEED_FSCK))
- return;
+ return 0;

trace_f2fs_issue_discard(bdev, dc->start, dc->len);

@@ -1057,43 +1057,44 @@ static void __submit_discard_cmd(struct f2fs_sb_info *sbi,
SECTOR_FROM_BLOCK(len),
GFP_NOFS, 0, &bio);
submit:
- if (!err && bio) {
- /*
- * should keep before submission to avoid D_DONE
- * right away
- */
+ if (err) {
spin_lock_irqsave(&dc->lock, flags);
- if (last)
+ if (dc->state == D_PARTIAL)
dc->state = D_SUBMIT;
- else
- dc->state = D_PARTIAL;
- dc->bio_ref++;
spin_unlock_irqrestore(&dc->lock, flags);

- atomic_inc(&dcc->issing_discard);
- dc->issuing++;
- list_move_tail(&dc->list, wait_list);
+ break;
+ }

- /* sanity check on discard range */
- __check_sit_bitmap(sbi, start, start + len);
+ f2fs_bug_on(sbi, !bio);

- bio->bi_private = dc;
- bio->bi_end_io = f2fs_submit_discard_endio;
- bio->bi_opf |= flag;
- submit_bio(bio);
+ /*
+ * should keep before submission to avoid D_DONE
+ * right away
+ */
+ spin_lock_irqsave(&dc->lock, flags);
+ if (last)
+ dc->state = D_SUBMIT;
+ else
+ dc->state = D_PARTIAL;
+ dc->bio_ref++;
+ spin_unlock_irqrestore(&dc->lock, flags);

- atomic_inc(&dcc->issued_discard);
+ atomic_inc(&dcc->issing_discard);
+ dc->issuing++;
+ list_move_tail(&dc->list, wait_list);

- f2fs_update_iostat(sbi, FS_DISCARD, 1);
- } else {
- spin_lock_irqsave(&dc->lock, flags);
- if (dc->state == D_PARTIAL)
- dc->state = D_SUBMIT;
- spin_unlock_irqrestore(&dc->lock, flags);
+ /* sanity check on discard range */
+ __check_sit_bitmap(sbi, start, start + len);

- __remove_discard_cmd(sbi, dc);
- err = -EIO;
- }
+ bio->bi_private = dc;
+ bio->bi_end_io = f2fs_submit_discard_endio;
+ bio->bi_opf |= flag;
+ submit_bio(bio);
+
+ atomic_inc(&dcc->issued_discard);
+
+ f2fs_update_iostat(sbi, FS_DISCARD, 1);

lstart += len;
start += len;
@@ -1101,8 +1102,9 @@ static void __submit_discard_cmd(struct f2fs_sb_info *sbi,
len = total_len;
}

- if (len)
+ if (!err && len)
__update_discard_tree_range(sbi, bdev, lstart, start, len);
+ return err;
}

static struct discard_cmd *__insert_discard_tree(struct f2fs_sb_info *sbi,
@@ -1308,6 +1310,7 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,

while (dc) {
struct rb_node *node;
+ int err = 0;

if (dc->state != D_PREP)
goto next;
@@ -1318,12 +1321,14 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
}

dcc->next_pos = dc->lstart + dc->len;
- __submit_discard_cmd(sbi, dpolicy, dc, &issued);
+ err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);

if (issued >= dpolicy->max_requests)
break;
next:
node = rb_next(&dc->rb_node);
+ if (err)
+ __remove_discard_cmd(sbi, dc);
dc = rb_entry_safe(node, struct discard_cmd, rb_node);
}

@@ -2577,6 +2582,7 @@ static unsigned int __issue_discard_cmd_range(struct f2fs_sb_info *sbi,

while (dc && dc->lstart <= end) {
struct rb_node *node;
+ int err = 0;

if (dc->len < dpolicy->granularity)
goto skip;
@@ -2586,11 +2592,14 @@ static unsigned int __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
goto skip;
}

- __submit_discard_cmd(sbi, dpolicy, dc, &issued);
+ err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);

if (issued >= dpolicy->max_requests) {
start = dc->lstart + dc->len;

+ if (err)
+ __remove_discard_cmd(sbi, dc);
+
blk_finish_plug(&plug);
mutex_unlock(&dcc->cmd_lock);
trimmed += __wait_all_discard_cmd(sbi, NULL);
@@ -2599,6 +2608,8 @@ static unsigned int __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
}
skip:
node = rb_next(&dc->rb_node);
+ if (err)
+ __remove_discard_cmd(sbi, dc);
dc = rb_entry_safe(node, struct discard_cmd, rb_node);

if (fatal_signal_pending(current))
--
2.18.0.rc1
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