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CIFS: fix deadlock in cached root handling

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commit 7e5a70ad88b1e6f6d9b934b2efb41afff496820f upstream.

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: 3d4ef9a15343 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Aurelien Aptel 2019-07-17 12:46:28 +02:00 committed by Greg Kroah-Hartman
parent f3160a1d71
commit e867ef1130
1 changed files with 44 additions and 0 deletions
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44
fs/cifs/smb2ops.c
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@ -553,7 +553,50 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
oparams.fid = pfid;
oparams.reconnect = false;
/*
* 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 = SMB2_open(xid, &oparams, &srch_path, &oplock, NULL, NULL, NULL);
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 critical section */
SMB2_close(xid, tcon, fid.persistent_fid,
fid.volatile_fid);
}
return 0;
}
/* Cached root is still invalid, continue normaly */
if (rc == 0) {
memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
tcon->crfid.tcon = tcon;
@ -561,6 +604,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
kref_init(&tcon->crfid.refcount);
kref_get(&tcon->crfid.refcount);
}
mutex_unlock(&tcon->crfid.fid_mutex);
return rc;
}