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bionic: prevent root processes from calling __system_property_add

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If a root process other than init calls __system_property_add, which
it should never do, it will break the design assumption that there is
only one mutator.

Pass O_EXCL to open() in map_prop_region_rw to ensure that only one
process ever has the property pages open for write.

(cherry picked from commit fb9b7b436f3ef94385f1b0c55ab81f246f0d96b8)

Change-Id: I6df3afedbfb5d07891b095aa24b78278381a5aaf
This commit is contained in:
Colin Cross 2013-06-16 10:19:16 -07:00
parent 1540f601be
commit 1d36ee1a6e
1 changed files with 16 additions and 2 deletions
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18
libc/bionic/system_properties.c
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@ -128,11 +128,13 @@ static int map_prop_area_rw()
{ {
prop_area *pa; prop_area *pa;
int fd; int fd;
int ret;
/* dev is a tmpfs that we can use to carve a shared workspace /* dev is a tmpfs that we can use to carve a shared workspace
* out of, so let's do that... * out of, so let's do that...
*/ */
fd = open(property_filename, O_RDWR | O_CREAT | O_NOFOLLOW, 0644); fd = open(property_filename, O_RDWR | O_CREAT | O_NOFOLLOW | O_CLOEXEC |
O_EXCL, 0444);
if (fd < 0) { if (fd < 0) {
if (errno == EACCES) { if (errno == EACCES) {
/* for consistency with the case where the process has already /* for consistency with the case where the process has already
@ -143,6 +145,10 @@ static int map_prop_area_rw()
return -1; return -1;
} }
ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
if (ret < 0)
goto out;
if (ftruncate(fd, PA_SIZE) < 0) if (ftruncate(fd, PA_SIZE) < 0)
goto out; goto out;
@ -186,8 +192,16 @@ static int map_prop_area()
{ {
bool fromFile = true; bool fromFile = true;
int result = -1; int result = -1;
int fd;
int ret;
int fd = open(property_filename, O_RDONLY | O_NOFOLLOW); fd = open(property_filename, O_RDONLY | O_NOFOLLOW | O_CLOEXEC);
if (fd >= 0) {
/* For old kernels that don't support O_CLOEXEC */
ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
if (ret < 0)
goto cleanup;
}
if ((fd < 0) && (errno == ENOENT)) { if ((fd < 0) && (errno == ENOENT)) {
/* /*