| Message ID | 20241215035828.106936-2-dennis.lamerice@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | ocfs2: fix slab-use-after-free due to dangling pointer dqi_priv | expand |
On 2024/12/15 11:58, Dennis Lam wrote: > When mounting ocfs2 and then remounting it as read-only, a > slab-use-after-free occurs after the user uses a syscall to > quota_getnextquota. Specifically, sb_dqinfo(sb, type)->dqi_priv is the > dangling pointer. > > During the remounting process, the pointer dqi_priv is freed but is > never set as null leaving it to to be accessed. Additionally, the > read-only option for remounting sets the DQUOT_SUSPENDED flag instead of > setting the DQUOT_USAGE_ENABLED flags. Moreover, later in the process of > getting the next quota, the function ocfs2_get_next_id is called and > only checks the quota usage flags and not the quota suspended flags. > > To fix this, I set dqi_priv to null when it is freed after remounting > with read-only and put a check for DQUOT_SUSPENDED in ocfs2_get_next_id. > > Signed-off-by: Dennis Lam <dennis.lamerice@gmail.com> > Reported-by: syzbot+d173bf8a5a7faeede34c@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/6731d26f.050a0220.1fb99c.014b.GAE@google.com/T/ > --- > fs/ocfs2/quota_global.c | 3 ++- > fs/ocfs2/quota_local.c | 1 + > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/fs/ocfs2/quota_global.c b/fs/ocfs2/quota_global.c > index 2b0daced98eb..c6d38340d6d4 100644 > --- a/fs/ocfs2/quota_global.c > +++ b/fs/ocfs2/quota_global.c > @@ -893,7 +893,8 @@ static int ocfs2_get_next_id(struct super_block *sb, struct kqid *qid) > int status = 0; > > trace_ocfs2_get_next_id(from_kqid(&init_user_ns, *qid), type); > - if (!sb_has_quota_loaded(sb, type)) { > + if (!sb_has_quota_loaded(sb, type) || > + sb_dqopt(sb)->flags & DQUOT_SUSPENDED) { Looks reasonable. We can just use !sb_has_quota_active() instead. Thanks, Joseph > status = -ESRCH; > goto out; > } > diff --git a/fs/ocfs2/quota_local.c b/fs/ocfs2/quota_local.c > index 73d3367c533b..2956d888c131 100644 > --- a/fs/ocfs2/quota_local.c > +++ b/fs/ocfs2/quota_local.c > @@ -867,6 +867,7 @@ static int ocfs2_local_free_info(struct super_block *sb, int type) > brelse(oinfo->dqi_libh); > brelse(oinfo->dqi_lqi_bh); > kfree(oinfo); > + info->dqi_priv = NULL; > return status; > } >
> > Looks reasonable. > We can just use !sb_has_quota_active() instead. > Thanks for the feedback. I'll be sure to send a new patch with the updated function. Regards, Dennis
diff --git a/fs/ocfs2/quota_global.c b/fs/ocfs2/quota_global.c index 2b0daced98eb..c6d38340d6d4 100644 --- a/fs/ocfs2/quota_global.c +++ b/fs/ocfs2/quota_global.c @@ -893,7 +893,8 @@ static int ocfs2_get_next_id(struct super_block *sb, struct kqid *qid) int status = 0; trace_ocfs2_get_next_id(from_kqid(&init_user_ns, *qid), type); - if (!sb_has_quota_loaded(sb, type)) { + if (!sb_has_quota_loaded(sb, type) || + sb_dqopt(sb)->flags & DQUOT_SUSPENDED) { status = -ESRCH; goto out; } diff --git a/fs/ocfs2/quota_local.c b/fs/ocfs2/quota_local.c index 73d3367c533b..2956d888c131 100644 --- a/fs/ocfs2/quota_local.c +++ b/fs/ocfs2/quota_local.c @@ -867,6 +867,7 @@ static int ocfs2_local_free_info(struct super_block *sb, int type) brelse(oinfo->dqi_libh); brelse(oinfo->dqi_lqi_bh); kfree(oinfo); + info->dqi_priv = NULL; return status; }
When mounting ocfs2 and then remounting it as read-only, a slab-use-after-free occurs after the user uses a syscall to quota_getnextquota. Specifically, sb_dqinfo(sb, type)->dqi_priv is the dangling pointer. During the remounting process, the pointer dqi_priv is freed but is never set as null leaving it to to be accessed. Additionally, the read-only option for remounting sets the DQUOT_SUSPENDED flag instead of setting the DQUOT_USAGE_ENABLED flags. Moreover, later in the process of getting the next quota, the function ocfs2_get_next_id is called and only checks the quota usage flags and not the quota suspended flags. To fix this, I set dqi_priv to null when it is freed after remounting with read-only and put a check for DQUOT_SUSPENDED in ocfs2_get_next_id. Signed-off-by: Dennis Lam <dennis.lamerice@gmail.com> Reported-by: syzbot+d173bf8a5a7faeede34c@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6731d26f.050a0220.1fb99c.014b.GAE@google.com/T/ --- fs/ocfs2/quota_global.c | 3 ++- fs/ocfs2/quota_local.c | 1 + 2 files changed, 3 insertions(+), 1 deletion(-)