[PATCH AUTOSEL 4.20 269/304] cifs: check ntwrk_buf_start for NULL before dereferencing it

Sasha Levin
2019-01-28T15:57:21Z

From: Ronnie Sahlberg <lsahlber@redhat.com>

[ Upstream commit 59a63e479ce36a3f24444c3a36efe82b78e4a8e0 ]

RHBZ: 1021460

There is an issue where when multiple threads open/close the same directory
ntwrk_buf_start might end up being NULL, causing the call to smbCalcSize
later to oops with a NULL deref.

The real bug is why this happens and why this can become NULL for an
open cfile, which should not be allowed.
This patch tries to avoid a oops until the time when we fix the underlying
issue.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/cifs/readdir.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/readdir.c b/fs/cifs/readdir.c
index e169e1a5fd35..3925a7bfc74d 100644
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -655,7 +655,14 @@ find_cifs_entry(const unsigned int xid, struct cifs_tcon *tcon, loff_t pos,
/* scan and find it */
int i;
char *cur_ent;
- char *end_of_smb = cfile->srch_inf.ntwrk_buf_start +
+ char *end_of_smb;
+
+ if (cfile->srch_inf.ntwrk_buf_start == NULL) {
+ cifs_dbg(VFS, "ntwrk_buf_start is NULL during readdir\n");
+ return -EIO;
+ }
+
+ end_of_smb = cfile->srch_inf.ntwrk_buf_start +
server->ops->calc_smb_size(
cfile->srch_inf.ntwrk_buf_start,
server);
--
2.19.1