From: Dan Carpenter dan.carpenter@oracle.com Subject: mm/mempolicy.c: fix out of bounds write in mpol_parse_str()

What we are trying to do is change the '=' character to a NUL terminator and then at the end of the function we restore it back to an '='. The problem is there are two error paths where we jump to the end of the function before we have replaced the '=' with NUL. We end up putting the '=' in the wrong place (possibly one element before the start of the buffer).

Link: http://lkml.kernel.org/r/20200115055426.vdjwvry44nfug7yy@kili.mountain Reported-by: syzbot+e64a13c5369a194d67df@syzkaller.appspotmail.com Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display") Signed-off-by: Dan Carpenter dan.carpenter@oracle.com Acked-by: Vlastimil Babka vbabka@suse.cz Dmitry Vyukov dvyukov@google.com Cc: Michal Hocko mhocko@kernel.org Cc: Dan Carpenter dan.carpenter@oracle.com Cc: Lee Schermerhorn lee.schermerhorn@hp.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Hugh Dickins hughd@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/mempolicy.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/mempolicy.c~mm-mempolicyc-fix-out-of-bounds-write-in-mpol_parse_str +++ a/mm/mempolicy.c @@ -2821,6 +2821,9 @@ int mpol_parse_str(char *str, struct mem char *flags = strchr(str, '='); int err = 1, mode;

+ if (flags) + *flags++ = '\0'; /* terminate mode string */ + if (nodelist) { /* NUL-terminate mode or flags string */ *nodelist++ = '\0'; @@ -2831,9 +2834,6 @@ int mpol_parse_str(char *str, struct mem } else nodes_clear(nodes);

- if (flags) - *flags++ = '\0'; /* terminate mode string */ - mode = match_string(policy_modes, MPOL_MAX, str); if (mode < 0) goto out; _