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https://github.com/Divested-Mobile/DivestOS-Build.git
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72 lines
2.8 KiB
Diff
72 lines
2.8 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Keith Mok <keithmok@google.com>
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Date: Thu, 31 Aug 2023 00:31:35 +0000
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Subject: [PATCH] Add seal if ashmem-dev is backed by memfd
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Need to seal the buffer size in align with ashmem if set to PROT_READ
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only to prevent untrusted remote process to shrink the buffer size and
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crash it.
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Bug: 294609150
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Test: build
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Ignore-AOSP-First: Security
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(cherry picked from commit f83c5c8fecf89d9315945368aa20350c2f235cc0)
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(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:61a2897733e15a12b7aa2dfd99957e83cbe59351)
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Merged-In: I9288cf30b41e84ad8d3247c204e20482912bff69
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Change-Id: I9288cf30b41e84ad8d3247c204e20482912bff69
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---
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libcutils/ashmem-dev.cpp | 29 +++++++++++++++++++++++++----
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1 file changed, 25 insertions(+), 4 deletions(-)
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diff --git a/libcutils/ashmem-dev.cpp b/libcutils/ashmem-dev.cpp
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index e67b45808..a081837e5 100644
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--- a/libcutils/ashmem-dev.cpp
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+++ b/libcutils/ashmem-dev.cpp
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@@ -360,6 +360,12 @@ static int memfd_create_region(const char* name, size_t size) {
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return -1;
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}
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+ // forbid size changes to match ashmem behaviour
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+ if (fcntl(fd, F_ADD_SEALS, F_SEAL_GROW | F_SEAL_SHRINK) == -1) {
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+ ALOGE("memfd_create(%s, %zd) F_ADD_SEALS failed: %m", name, size);
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+ return -1;
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+ }
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+
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if (debug_log) {
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ALOGE("memfd_create(%s, %zd) success. fd=%d\n", name, size, fd.get());
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}
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@@ -411,14 +417,29 @@ error:
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}
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static int memfd_set_prot_region(int fd, int prot) {
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- /* Only proceed if an fd needs to be write-protected */
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+ int seals = fcntl(fd, F_GET_SEALS);
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+ if (seals == -1) {
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+ ALOGE("memfd_set_prot_region(%d, %d): F_GET_SEALS failed: %s\n", fd, prot, strerror(errno));
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+ return -1;
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+ }
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+
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if (prot & PROT_WRITE) {
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+ /* Now we want the buffer to be read-write, let's check if the buffer
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+ * has been previously marked as read-only before, if so return error
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+ */
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+ if (seals & F_SEAL_FUTURE_WRITE) {
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+ ALOGE("memfd_set_prot_region(%d, %d): region is write protected\n", fd, prot);
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+ errno = EINVAL; // inline with ashmem error code, if already in
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+ // read-only mode
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+ return -1;
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+ }
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return 0;
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}
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- if (fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE) == -1) {
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- ALOGE("memfd_set_prot_region(%d, %d): F_SEAL_FUTURE_WRITE seal failed: %s\n", fd, prot,
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- strerror(errno));
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+ /* We would only allow read-only for any future file operations */
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+ if (fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE | F_SEAL_SEAL) == -1) {
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+ ALOGE("memfd_set_prot_region(%d, %d): F_SEAL_FUTURE_WRITE | F_SEAL_SEAL seal failed: %s\n",
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+ fd, prot, strerror(errno));
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return -1;
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}
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