cifs: fix session state transition to avoid use-after-free issue
cifs: fix session state transition to avoid use-after-free issue
JIRA: https://issues.redhat.com/browse/RHEL-20534
This patch is a backport of the following upstream commit:
commit ff7d80a9f2711bf3d9fe1cfb70b3fd15c50584b7 Author: Winston Wen wentao@uniontech.com Date: Mon Jun 26 11:42:55 2023 +0800
cifs: fix session state transition to avoid use-after-free issue
We switch session state to SES_EXITING without cifs_tcp_ses_lock now,
it may lead to potential use-after-free issue.
Consider the following execution processes:
Thread 1:
__cifs_put_smb_ses()
spin_lock(&cifs_tcp_ses_lock)
if (--ses->ses_count > 0)
spin_unlock(&cifs_tcp_ses_lock)
return
spin_unlock(&cifs_tcp_ses_lock)
---> **GAP**
spin_lock(&ses->ses_lock)
if (ses->ses_status == SES_GOOD)
ses->ses_status = SES_EXITING
spin_unlock(&ses->ses_lock)
Thread 2:
cifs_find_smb_ses()
spin_lock(&cifs_tcp_ses_lock)
list_for_each_entry(ses, ...)
spin_lock(&ses->ses_lock)
if (ses->ses_status == SES_EXITING)
spin_unlock(&ses->ses_lock)
continue
...
spin_unlock(&ses->ses_lock)
if (ret)
cifs_smb_ses_inc_refcount(ret)
spin_unlock(&cifs_tcp_ses_lock)
If thread 1 is preempted in the gap and thread 2 start executing, thread 2
will get the session, and soon thread 1 will switch the session state to
SES_EXITING and start releasing it, even though thread 1 had increased the
session's refcount and still uses it.
So switch session state under cifs_tcp_ses_lock to eliminate this gap.
Signed-off-by: Winston Wen <wentao@uniontech.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Jay Shin jaeshin@redhat.com