Fri, Sep 20, 2019 at 14:08, Pavel Shilovsky piastryyy@gmail.com:
From: Aurelien Aptel aaptel@suse.com
Commit 7e5a70ad88b1 ("CIFS: fix deadlock in cached root handling") 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.
CC: stable@vger.kernel.org # v4.19+ Link: https://lore.kernel.org/linux-cifs/684ed01c-cbca-2716-bc28-b0a59a0f8521@prod... Fixes: 3d4ef9a15343 ("smb3: fix redundant opens on root") Signed-off-by: Aurelien Aptel aaptel@suse.com Signed-off-by: Pavel Shilovsky pshilov@microsoft.com
fs/cifs/smb2ops.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+)
diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c index cc9e846a3865..094be406cde4 100644 --- a/fs/cifs/smb2ops.c +++ b/fs/cifs/smb2ops.c @@ -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;}
2.17.1
Forgot to mention that kernels 5.1.y and above already have the appropriate patch. This is a backport for 4.19.
-- Best regards, Pavel Shilovsky