Hi Tianjia,
On Tue, 2023-05-30 at 20:14 +0800, Tianjia Zhang wrote:
> When integrity_inode_get() is querying and inserting the cache, there
> is a conditional race in the concurrent environment.
>
> Query iint within the read-lock. If there is no result, allocate iint
> first and insert the iint cache in the write-lock protection. When the
> iint cache does not exist, and when multiple execution streams come at
> the same time, there will be a race condition, and multiple copies of
> iint will be allocated at the same time, and then put into the cache
> one by one under the write-lock protection.
Right, the race condition is the result of not properly implementing
"double-checked locking". In this case, it first checks to see if the
iint cache record exists before taking the lock, but doesn't check
again after taking the integrity_iint_lock.
>
> This is mainly because the red-black tree insertion does not perform
> duplicate detection. This is not the desired result, when this
> happens, the repeated allocation should be freed and the existing
> iint cache should be returned.
>
> Fixes: bf2276d10ce5 ("ima: allocating iint improvements")
> Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
> Cc: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v3.10+
> ---
> security/integrity/iint.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/security/integrity/iint.c b/security/integrity/iint.c
> index c73858e8c6d5..d49c843a88ee 100644
> --- a/security/integrity/iint.c
> +++ b/security/integrity/iint.c
> @@ -43,12 +43,10 @@ static struct integrity_iint_cache *__integrity_iint_find(struct inode *inode)
> else if (inode > iint->inode)
> n = n->rb_right;
> else
> - break;
> + return iint;
> }
> - if (!n)
> - return NULL;
>
> - return iint;
> + return NULL;
> }
>
> /*
> @@ -115,8 +113,13 @@ struct integrity_iint_cache *integrity_inode_get(struct inode *inode)
> rb_node);
> if (inode < test_iint->inode)
> p = &(*p)->rb_left;
> - else
> + else if (inode > test_iint->inode)
> p = &(*p)->rb_right;
> + else {
> + write_unlock(&integrity_iint_lock);
> + kmem_cache_free(iint_cache, iint);
> + return test_iint;
> + }
> }
>
> iint->inode = inode;
scripts/checkpatch.pl with the -strict option complains:
CHECK: Unbalanced braces around else statement
#56: FILE: security/integrity/iint.c:118:
+ else {
total: 0 errors, 0 warnings, 1 checks, 28 lines checked
--
thanks,
Mimi
