The patch titled
Subject: ipc/shm: fix shmat() nil address after round-down when remapping
has been added to the -mm tree. Its filename is
ipc-shm-fix-shmat-nil-address-after-round-down-when-remapping.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-shm-fix-shmat-nil-address-after-round-down-when-remapping.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-shm-fix-shmat-nil-address-after-round-down-when-remapping.patch
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------------------------------------------------------
From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Subject: ipc/shm: fix shmat() nil address after round-down when remapping
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@xxxxxxx>
Reported-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/shm.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff -puN ipc/shm.c~ipc-shm-fix-shmat-nil-address-after-round-down-when-remapping ipc/shm.c
--- a/ipc/shm.c~ipc-shm-fix-shmat-nil-address-after-round-down-when-remapping
+++ a/ipc/shm.c
@@ -1363,9 +1363,17 @@ long do_shmat(int shmid, char __user *sh
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
_
Patches currently in -mm which might be from dave@xxxxxxxxxxxx are
ipc-sem-mitigate-semnum-index-against-spectre-v1.patch
revert-ipc-shm-fix-shmat-mmap-nil-page-protection.patch
ipc-shm-fix-shmat-nil-address-after-round-down-when-remapping.patch
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