[SRU][J/N][PATCH 0/1] net/rds: reset op_nents when zerocopy page pin fails

[Benjamin Wheeler]

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2153962

SRU Justification:

[Impact]

When iov_iter_get_pages2() fails in rds_message_zcopy_from_user(),
the pinned pages are released with put_page(), and
rm->data.op_mmp_znotifier is cleared.  But we fail to properly
clear rm->data.op_nents.

Later when rds_message_purge() is called from rds_sendmsg() the
cleanup loop iterates over the incorrectly non zero number of
op_nents and frees them again.


[Fix]

Fix this by properly resetting op_nents when it should be in
rds_message_zcopy_from_user().

[Test Plan]

Compiled, boot tested, and ran reproducer (found at 
https://github.com/v12-security/pocs/tree/main/pintheft).


[Where problems could occur]

The fix is a single line change to the rds_message_zcopy_from_user()
function, which is only called from rds_sendmsg() when the caller has
requested zero-copy send.  If there are any issues with this patch, they
would likely be limited to zero-copy send operations in RDS.


Allison Henderson (1):
  net/rds: reset op_nents when zerocopy page pin fails

 net/rds/message.c | 1 +
 1 file changed, 1 insertion(+)

-- 
2.43.0