4.4-stable review patch. If anyone has any objections, please let me know.
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From: Davidlohr Bueso dave@stgolabs.net
commit 8f89c007b6dec16a1793cb88de88fcc02117bbbc upstream.
shmat()'s SHM_REMAP option forbids passing a nil address for; this is in fact the very first thing we check for. Andrea reported that for SHM_RND|SHM_REMAP cases we can end up bypassing the initial addr check, but we need to check again if the address was rounded down to nil. As of this patch, such cases will return -EINVAL.
Link: http://lkml.kernel.org/r/20180503204934.kk63josdu6u53fbd@linux-n805 Signed-off-by: Davidlohr Bueso dbueso@suse.de Reported-by: Andrea Arcangeli aarcange@redhat.com Cc: Joe Lawrence joe.lawrence@redhat.com Cc: Manfred Spraul manfred@colorfullife.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- ipc/shm.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
--- a/ipc/shm.c +++ b/ipc/shm.c @@ -1113,9 +1113,17 @@ long do_shmat(int shmid, char __user *sh goto out; else if ((addr = (ulong)shmaddr)) { if (addr & (shmlba - 1)) { - if (shmflg & SHM_RND) + if (shmflg & SHM_RND) { addr &= ~(shmlba - 1); /* round down */ - else + + /* + * Ensure that the round-down is non-nil + * when remapping. This can happen for + * cases when addr < shmlba. + */ + if (!addr && (shmflg & SHM_REMAP)) + goto out; + } else #ifndef __ARCH_FORCE_SHMLBA if (addr & ~PAGE_MASK) #endif