4.9-stable review patch. If anyone has any objections, please let me know.
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From: Pavel Shilovsky pshilov@microsoft.com
commit ef68e831840c40c7d01b328b3c0f5d8c4796c232 upstream.
When executing add_credits() we currently call cifs_reconnect() if the number of credits is zero and there are no requests in flight. In this case we may call cifs_reconnect() recursively twice and cause memory corruption given the following sequence of functions:
mid1.callback() -> add_credits() -> cifs_reconnect() -> -> mid2.callback() -> add_credits() -> cifs_reconnect().
Fix this by avoiding to call cifs_reconnect() in add_credits() and checking for zero credits in the demultiplex thread.
Cc: stable@vger.kernel.org Signed-off-by: Pavel Shilovsky pshilov@microsoft.com Reviewed-by: Ronnie Sahlberg lsahlber@redhat.com Signed-off-by: Steve French stfrench@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/cifs/connect.c | 21 +++++++++++++++++++++ fs/cifs/smb2ops.c | 32 +++++++++++++++++++++++++------- 2 files changed, 46 insertions(+), 7 deletions(-)
--- a/fs/cifs/connect.c +++ b/fs/cifs/connect.c @@ -518,6 +518,21 @@ server_unresponsive(struct TCP_Server_In return false; }
+static inline bool +zero_credits(struct TCP_Server_Info *server) +{ + int val; + + spin_lock(&server->req_lock); + val = server->credits + server->echo_credits + server->oplock_credits; + if (server->in_flight == 0 && val == 0) { + spin_unlock(&server->req_lock); + return true; + } + spin_unlock(&server->req_lock); + return false; +} + static int cifs_readv_from_socket(struct TCP_Server_Info *server, struct msghdr *smb_msg) { @@ -530,6 +545,12 @@ cifs_readv_from_socket(struct TCP_Server for (total_read = 0; msg_data_left(smb_msg); total_read += length) { try_to_freeze();
+ /* reconnect if no credits and no requests in flight */ + if (zero_credits(server)) { + cifs_reconnect(server); + return -ECONNABORTED; + } + if (server_unresponsive(server)) return -ECONNABORTED;
--- a/fs/cifs/smb2ops.c +++ b/fs/cifs/smb2ops.c @@ -30,6 +30,7 @@ #include "smb2glob.h" #include "cifs_ioctl.h"
+/* Change credits for different ops and return the total number of credits */ static int change_conf(struct TCP_Server_Info *server) { @@ -37,17 +38,15 @@ change_conf(struct TCP_Server_Info *serv server->oplock_credits = server->echo_credits = 0; switch (server->credits) { case 0: - return -1; + return 0; case 1: server->echoes = false; server->oplocks = false; - cifs_dbg(VFS, "disabling echoes and oplocks\n"); break; case 2: server->echoes = true; server->oplocks = false; server->echo_credits = 1; - cifs_dbg(FYI, "disabling oplocks\n"); break; default: server->echoes = true; @@ -60,14 +59,15 @@ change_conf(struct TCP_Server_Info *serv server->echo_credits = 1; } server->credits -= server->echo_credits + server->oplock_credits; - return 0; + return server->credits + server->echo_credits + server->oplock_credits; }
static void smb2_add_credits(struct TCP_Server_Info *server, const unsigned int add, const int optype) { - int *val, rc = 0; + int *val, rc = -1; + spin_lock(&server->req_lock); val = server->ops->get_credits_field(server, optype); *val += add; @@ -91,8 +91,26 @@ smb2_add_credits(struct TCP_Server_Info } spin_unlock(&server->req_lock); wake_up(&server->request_q); - if (rc) - cifs_reconnect(server); + + if (server->tcpStatus == CifsNeedReconnect) + return; + + switch (rc) { + case -1: + /* change_conf hasn't been executed */ + break; + case 0: + cifs_dbg(VFS, "Possible client or server bug - zero credits\n"); + break; + case 1: + cifs_dbg(VFS, "disabling echoes and oplocks\n"); + break; + case 2: + cifs_dbg(FYI, "disabling oplocks\n"); + break; + default: + cifs_dbg(FYI, "add %u credits total=%d\n", add, rc); + } }
static void