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CIFS: fix deadlock in cached root handling

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Prevent deadlock between open_shroot() and
cifs_mark_open_files_invalid() by releasing the lock before entering
SMB2_open, taking it again after and checking if we still need to use
the result.

Link: https://lore.kernel.org/linux-cifs/684ed01c-cbca-2716-bc28-b0a59a0f8521@prodrive-technologies.com/T/#u
Fixes: 3d4ef9a153 ("smb3: fix redundant opens on root")
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org>
This commit is contained in:
Aurelien Aptel 2019-07-17 12:46:28 +02:00 committed by Steve French
parent ae9b728c8d
commit 7e5a70ad88
1 changed files with 45 additions and 1 deletions
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44
fs/cifs/smb2ops.c
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@ -694,8 +694,51 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
smb2_set_related(&rqst[1]);
/*
* We do not hold the lock for the open because in case
* SMB2_open needs to reconnect, it will end up calling
* cifs_mark_open_files_invalid() which takes the lock again
* thus causing a deadlock
*/
mutex_unlock(&tcon->crfid.fid_mutex);
rc = compound_send_recv(xid, ses, flags, 2, rqst,
resp_buftype, rsp_iov);
mutex_lock(&tcon->crfid.fid_mutex);
/*
* Now we need to check again as the cached root might have
* been successfully re-opened from a concurrent process
*/
if (tcon->crfid.is_valid) {
/* work was already done */
/* stash fids for close() later */
struct cifs_fid fid = {
.persistent_fid = pfid->persistent_fid,
.volatile_fid = pfid->volatile_fid,
};
/*
* caller expects this func to set pfid to a valid
* cached root, so we copy the existing one and get a
* reference.
*/
memcpy(pfid, tcon->crfid.fid, sizeof(*pfid));
kref_get(&tcon->crfid.refcount);
mutex_unlock(&tcon->crfid.fid_mutex);
if (rc == 0) {
/* close extra handle outside of crit sec */
SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
}
goto oshr_free;
}
/* Cached root is still invalid, continue normaly */
if (rc)
goto oshr_exit;
@ -731,6 +774,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
oshr_exit:
mutex_unlock(&tcon->crfid.fid_mutex);
oshr_free:
SMB2_open_free(&rqst[0]);
SMB2_query_info_free(&rqst[1]);
free_rsp_buf(resp_buftype[0], rsp_iov[0].iov_base);