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cifs: fix potential deadlock in cache_refresh_path()

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[ Upstream commit 9fb0db4051 ]

Avoid getting DFS referral from an exclusive lock in
cache_refresh_path() because the tcon IPC used for getting the
referral could be disconnected and thus causing a deadlock as shown
below:

task A                       task B
======                       ======
cifs_demultiplex_thread()    dfs_cache_find()
 cifs_handle_standard()       cache_refresh_path()
  reconnect_dfs_server()       down_write()
   dfs_cache_noreq_find()       get_dfs_referral()
    down_read() <- deadlock      smb2_get_dfs_refer()
                                  SMB2_ioctl()
				   cifs_send_recv()
				    compound_send_recv()
				     wait_for_response()

where task A cannot wake up task B because it is blocked on
down_read() due to the exclusive lock held in cache_refresh_path() and
therefore not being able to make progress.

Fixes: c9f7110399 ("cifs: keep referral server sessions alive")
Reviewed-by: Aurélien Aptel <aurelien.aptel@gmail.com>
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Paulo Alcantara 2023-01-17 19:00:37 -03:00 committed by Greg Kroah-Hartman
parent d5fb544b4c
commit a8a518ff3b
1 changed files with 23 additions and 19 deletions
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42
fs/cifs/dfs_cache.c
View file

@ -792,26 +792,27 @@ static int get_dfs_referral(const unsigned int xid, struct cifs_ses *ses, const
*/
static int cache_refresh_path(const unsigned int xid, struct cifs_ses *ses, const char *path)
{
int rc;
struct cache_entry *ce;
struct dfs_info3_param *refs = NULL;
struct cache_entry *ce;
int numrefs = 0;
bool newent = false;
int rc;
cifs_dbg(FYI, "%s: search path: %s\n", __func__, path);
down_write(&htable_rw_lock);
down_read(&htable_rw_lock);
ce = lookup_cache_entry(path);
if (!IS_ERR(ce)) {
if (!cache_entry_expired(ce)) {
dump_ce(ce);
up_write(&htable_rw_lock);
return 0;
}
} else {
newent = true;
if (!IS_ERR(ce) && !cache_entry_expired(ce)) {
up_read(&htable_rw_lock);
return 0;
}
/*
* Unlock shared access as we don't want to hold any locks while getting
* a new referral. The @ses used for performing the I/O could be
* reconnecting and it acquires @htable_rw_lock to look up the dfs cache
* in order to failover -- if necessary.
*/
up_read(&htable_rw_lock);
/*
* Either the entry was not found, or it is expired.
@ -819,19 +820,22 @@ static int cache_refresh_path(const unsigned int xid, struct cifs_ses *ses, cons
*/
rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
if (rc)
goto out_unlock;
goto out;
dump_refs(refs, numrefs);
if (!newent) {
rc = update_cache_entry_locked(ce, refs, numrefs);
goto out_unlock;
down_write(&htable_rw_lock);
/* Re-check as another task might have it added or refreshed already */
ce = lookup_cache_entry(path);
if (!IS_ERR(ce)) {
if (cache_entry_expired(ce))
rc = update_cache_entry_locked(ce, refs, numrefs);
} else {
rc = add_cache_entry_locked(refs, numrefs);
}
rc = add_cache_entry_locked(refs, numrefs);
out_unlock:
up_write(&htable_rw_lock);
out:
free_dfs_info_array(refs, numrefs);
return rc;
}