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cifs: check ntwrk_buf_start for NULL before dereferencing it

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[ Upstream commit 59a63e479c ]

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>
This commit is contained in:
Ronnie Sahlberg 2018-12-13 08:06:16 +10:00 • committed by Greg Kroah-Hartman
commit 5d3b4cd873
1 changed files with 8 additions and 1 deletions
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9
fs/cifs/readdir.c
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@ -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);