Hello,
I have some questions regarding CVE-2024-26928.
I would like to confirm whether the phrase "fix potential UAF in
cifs_debug_files_proc_show()" implies that the UAF issue does not
actually exist, correct?
Based on my analysis, `cifs_tcp_ses_lock` plays a crucial role in
preventing the UAF.
After adding `ses` to the `smb_ses_list` list, the only place where
the `ses` is freed is in the `__cifs_put_smb_ses` function:
```
__cifs_put_smb_ses()
...
spin_lock(&cifs_tcp_ses_lock);
list_del_init(&ses->smb_ses_list);
spin_unlock(&cifs_tcp_ses_lock);
...
sesInfoFree(ses);
```
The `ses` is freed only after it is removed from the list, and this
removal is protected by `cifs_tcp_ses_lock`.
In `cifs_debug_files_proc_show()`, the `cifs_tcp_ses_lock` is still
held, ensuring that during access to the `ses` that is about to be
destroyed, the `ses` will not be freed in `__cifs_put_smb_ses()`,
thus preventing a UAF issue.
```
cifs_debug_files_proc_show()
...
spin_lock(&cifs_tcp_ses_lock);
...
list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list)
...
spin_lock(&cifs_tcp_ses_lock);
```
Based on this understanding, I wonder if the issue addressed by
this CVE might not be a genuine problem. I am also curious about
the series of patches considered as fixes for this CVE.
Best regards,
Wang Zhaolong
Skip sessions that are being teared down (status == SES_EXITING) to
avoid UAF.
Signed-off-by: Paulo Alcantara (Red Hat) <pc@xxxxxxxxxxxxx>
---
fs/smb/client/cifs_debug.c | 2 ++
fs/smb/client/cifsglob.h | 10 ++++++++++
2 files changed, 12 insertions(+)
diff --git a/fs/smb/client/cifs_debug.c b/fs/smb/client/cifs_debug.c
index 226d4835c92d..c9aec9a38ad3 100644
--- a/fs/smb/client/cifs_debug.c
+++ b/fs/smb/client/cifs_debug.c
@@ -250,6 +250,8 @@ static int cifs_debug_files_proc_show(struct seq_file *m, void *v)
spin_lock(&cifs_tcp_ses_lock);
list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
+ if (cifs_ses_exiting(ses))
+ continue;
list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
spin_lock(&tcon->open_file_lock);
list_for_each_entry(cfile, &tcon->openFileList, tlist) {
diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 286afbe346be..f67607319c43 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -2322,4 +2322,14 @@ struct smb2_compound_vars {
struct kvec ea_iov;
};
+static inline bool cifs_ses_exiting(struct cifs_ses *ses)
+{
+ bool ret;
+
+ spin_lock(&ses->ses_lock);
+ ret = ses->ses_status == SES_EXITING;
+ spin_unlock(&ses->ses_lock);
+ return ret;
+}
+
#endif /* _CIFS_GLOB_H */
