Hi Joseph and Changwei,
On 2018/3/30 9:26, Joseph Qi wrote:
>
>
> On 18/3/29 10:06, Changwei Ge wrote:
>> ocfs2_read_blocks() is used to read several blocks from disk.
>> Currently, the input argument *bhs* can be NULL or NOT. It depends on
>> the caller's behavior. If the function fails in reading blocks from
>> disk, the corresponding bh will be assigned to NULL and put.
>>
>> Obviously, above process for non-NULL input bh is not appropriate.
>> Because the caller doesn't even know its bhs are put and re-assigned.
>>
>> If buffer head is managed by caller, ocfs2_read_blocks should not
>> evaluate it to NULL. It will cause caller accessing illegal memory,
>> thus crash.
>>
>> Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
>> ---
>> fs/ocfs2/buffer_head_io.c | 31 +++++++++++++++++++++++++------
>> 1 file changed, 25 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/ocfs2/buffer_head_io.c b/fs/ocfs2/buffer_head_io.c
>> index d9ebe11..17329b6 100644
>> --- a/fs/ocfs2/buffer_head_io.c
>> +++ b/fs/ocfs2/buffer_head_io.c
>> @@ -188,6 +188,7 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
>> int i, ignore_cache = 0;
>> struct buffer_head *bh;
>> struct super_block *sb = ocfs2_metadata_cache_get_super(ci);
>> + int new_bh = 0;
>>
>> trace_ocfs2_read_blocks_begin(ci, (unsigned long long)block, nr, flags);
>>
>> @@ -213,6 +214,18 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
>> goto bail;
>> }
>>
>> + /* Use below trick to check if all bhs are NULL or assigned.
>> + * Basically, we hope all bhs are consistent so that we can
>> + * handle exception easily.
>> + */
>> + new_bh = (bhs[0] == NULL);
>> + for (i = 1 ; i < nr ; i++) {
>> + if ((new_bh && bhs[i]) || (!new_bh && !bhs[i])) {
>> + WARN(1, "Not all bhs are consistent\n");
>> + break;
>> + }
>> + }
>> +
>> ocfs2_metadata_cache_io_lock(ci);
>> for (i = 0 ; i < nr ; i++) {
>> if (bhs[i] == NULL) {
>> @@ -324,8 +337,10 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
>> if (!(flags & OCFS2_BH_READAHEAD)) {
>> if (status) {
>> /* Clear the rest of the buffers on error */
>> - put_bh(bh);
>> - bhs[i] = NULL;
>> + if (new_bh) {
>> + put_bh(bh);
>> + bhs[i] = NULL;
>> + }
>
> Since we assume caller has to pass either all NULL or all non-NULL,
> here we will only put bh internal allocated. Am I missing something?
I think this branch will put bh external allocated as 'new_bh' only means
bhs[0] is internal allocated. So this branch seems inappropriate.
thanks,
Jun
>
> Thanks,
> Joseph
>
>> continue;
>> }
>> /* We know this can't have changed as we hold the
>> @@ -342,8 +357,10 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
>> * for this bh as it's not marked locally
>> * uptodate. */
>> status = -EIO;
>> - put_bh(bh);
>> - bhs[i] = NULL;
>> + if (new_bh) {
>> + put_bh(bh);
>> + bhs[i] = NULL;
>> + }
>> continue;
>> }
>>
>> @@ -355,8 +372,10 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
>> clear_buffer_needs_validate(bh);
>> status = validate(sb, bh);
>> if (status) {
>> - put_bh(bh);
>> - bhs[i] = NULL;
>> + if (new_bh) {
>> + put_bh(bh);
>> + bhs[i] = NULL;
>> + }
>> continue;
>> }
>> }
>>
> .
>