Hi,
Static analysis using Coverity has detected a potential null pointer
dereference after a null check in the following commit:
commit 5fdb322ff2c2b4ad519f490dcb7ebb96c5439af7
Author: Daeho Jeong <[email protected]>
Date: Thu Dec 3 15:56:15 2020 +0900
f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE
The analysis is as follows:
4025 static int redirty_blocks(struct inode *inode, pgoff_t page_idx,
int len)
4026 {
4027 DEFINE_READAHEAD(ractl, NULL, inode->i_mapping, page_idx);
4028 struct address_space *mapping = inode->i_mapping;
4029 struct page *page;
4030 pgoff_t redirty_idx = page_idx;
4031 int i, page_len = 0, ret = 0;
4032
4033 page_cache_ra_unbounded(&ractl, len, 0);
4034
1. Condition i < len, taking true branch.
4. Condition i < len, taking true branch.
4035 for (i = 0; i < len; i++, page_idx++) {
4036 page = read_cache_page(mapping, page_idx, NULL, NULL);
2. Condition IS_ERR(page), taking false branch.
5. Condition IS_ERR(page), taking true branch.
4037 if (IS_ERR(page)) {
4038 ret = PTR_ERR(page);
6. Breaking from loop.
4039 break;
4040 }
4041 page_len++;
3. Jumping back to the beginning of the loop.
4042 }
4043
7. Condition i < page_len, taking true branch.
4044 for (i = 0; i < page_len; i++, redirty_idx++) {
4045 page = find_lock_page(mapping, redirty_idx);
8. Condition !page, taking true branch.
9. var_compare_op: Comparing page to null implies that page might be
null.
4046 if (!page)
4047 ret = -ENOENT;
Dereference after null check (FORWARD_NULL)
10. var_deref_model: Passing null pointer page to set_page_dirty,
which dereferences it.
4048 set_page_dirty(page);
4049 f2fs_put_page(page, 1);
4050 f2fs_put_page(page, 0);
4051 }
4052
4053 return ret;
4054 }
The !page check on line 4046 sets ret appropriately but we have a
following call to set_page_dirty on a null page that causes the error.
Not sure how this should be fixed, should the check bail out immediately
or just avoid the following set_page_dirty anf f2fs_put_page calls?
Colin
Hi Colin,
Thanks for notifying me. We need to just continue without
set_page_dirty() and f2fs_put_page().
2021년 1월 4일 (월) 오후 11:43, Colin Ian King <[email protected]>님이 작성:
>
> Hi,
>
> Static analysis using Coverity has detected a potential null pointer
> dereference after a null check in the following commit:
>
> commit 5fdb322ff2c2b4ad519f490dcb7ebb96c5439af7
> Author: Daeho Jeong <[email protected]>
> Date: Thu Dec 3 15:56:15 2020 +0900
>
> f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE
>
> The analysis is as follows:
>
> 4025 static int redirty_blocks(struct inode *inode, pgoff_t page_idx,
> int len)
> 4026 {
> 4027 DEFINE_READAHEAD(ractl, NULL, inode->i_mapping, page_idx);
> 4028 struct address_space *mapping = inode->i_mapping;
> 4029 struct page *page;
> 4030 pgoff_t redirty_idx = page_idx;
> 4031 int i, page_len = 0, ret = 0;
> 4032
> 4033 page_cache_ra_unbounded(&ractl, len, 0);
> 4034
>
> 1. Condition i < len, taking true branch.
> 4. Condition i < len, taking true branch.
>
> 4035 for (i = 0; i < len; i++, page_idx++) {
> 4036 page = read_cache_page(mapping, page_idx, NULL, NULL);
>
> 2. Condition IS_ERR(page), taking false branch.
> 5. Condition IS_ERR(page), taking true branch.
>
> 4037 if (IS_ERR(page)) {
> 4038 ret = PTR_ERR(page);
>
> 6. Breaking from loop.
>
> 4039 break;
> 4040 }
> 4041 page_len++;
>
> 3. Jumping back to the beginning of the loop.
>
> 4042 }
> 4043
>
> 7. Condition i < page_len, taking true branch.
>
> 4044 for (i = 0; i < page_len; i++, redirty_idx++) {
> 4045 page = find_lock_page(mapping, redirty_idx);
>
> 8. Condition !page, taking true branch.
> 9. var_compare_op: Comparing page to null implies that page might be
> null.
>
> 4046 if (!page)
> 4047 ret = -ENOENT;
>
> Dereference after null check (FORWARD_NULL)
>
> 10. var_deref_model: Passing null pointer page to set_page_dirty,
> which dereferences it.
>
> 4048 set_page_dirty(page);
> 4049 f2fs_put_page(page, 1);
> 4050 f2fs_put_page(page, 0);
> 4051 }
> 4052
> 4053 return ret;
> 4054 }
>
> The !page check on line 4046 sets ret appropriately but we have a
> following call to set_page_dirty on a null page that causes the error.
> Not sure how this should be fixed, should the check bail out immediately
> or just avoid the following set_page_dirty anf f2fs_put_page calls?
>
> Colin
>
>
>
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