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authorDavidlohr Bueso <dave@stgolabs.net>2018-05-25 14:47:30 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-05-30 07:51:49 +0200
commitafdc490b36b02426f54c166eb794fc009c48a6de (patch)
treec9bc7e9bf5040caf96d1c71224bb2de693ecc5b2 /ipc
parent67dd0bad818914614e77c00ca2f259d2ad69f5a3 (diff)
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ipc/shm: fix shmat() nil address after round-down when remapping
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>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/shm.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/ipc/shm.c b/ipc/shm.c
index 6e42914f17ba..44cca2529a95 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1309,9 +1309,17 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg,
if (addr) {
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