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Subject[PATCH 4.18 134/235] cifs: prevent integer overflow in nxt_dir_entry()
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4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@oracle.com>

commit 8ad8aa353524d89fa2e09522f3078166ff78ec42 upstream.

The "old_entry + le32_to_cpu(pDirInfo->NextEntryOffset)" can wrap
around so I have added a check for integer overflow.

Reported-by: Dr Silvio Cesare of InfoSect <silvio.cesare@gmail.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/cifs/readdir.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -376,8 +376,15 @@ static char *nxt_dir_entry(char *old_ent

new_entry = old_entry + sizeof(FIND_FILE_STANDARD_INFO) +
pfData->FileNameLength;
- } else
- new_entry = old_entry + le32_to_cpu(pDirInfo->NextEntryOffset);
+ } else {
+ u32 next_offset = le32_to_cpu(pDirInfo->NextEntryOffset);
+
+ if (old_entry + next_offset < old_entry) {
+ cifs_dbg(VFS, "invalid offset %u\n", next_offset);
+ return NULL;
+ }
+ new_entry = old_entry + next_offset;
+ }
cifs_dbg(FYI, "new entry %p old entry %p\n", new_entry, old_entry);
/* validate that new_entry is not past end of SMB */
if (new_entry >= end_of_smb) {

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