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Ensure that readlink has access to /proc/self/fd

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/proc/self/fd is not available when PR_DUMPABLE is set to 0
which is default for the user builds. It leads to permission
denials on readlink.

This change fixes the problem by setting PR_DUMPABLE flag to 1
for readlink and restoring it's previous value after the call.

Bug: http://b/24912743
Change-Id: I3fd179c5c6b56af96d6a15ee597024ccb15e1a13
This commit is contained in:
Dmitriy Ivanov 2015-10-14 11:15:45 -07:00
parent f32b689d3d
commit cf92738fa5
1 changed files with 8 additions and 0 deletions
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8
linker/linker.cpp
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@ -37,6 +37,7 @@
#include <string.h> #include <string.h>
#include <sys/mman.h> #include <sys/mman.h>
#include <sys/param.h> #include <sys/param.h>
#include <sys/prctl.h>
#include <unistd.h> #include <unistd.h>
#include <new> #include <new>
@ -317,6 +318,13 @@ static void parse_LD_PRELOAD(const char* path) {
static bool realpath_fd(int fd, std::string* realpath) { static bool realpath_fd(int fd, std::string* realpath) {
std::vector<char> buf(PATH_MAX), proc_self_fd(PATH_MAX); std::vector<char> buf(PATH_MAX), proc_self_fd(PATH_MAX);
snprintf(&proc_self_fd[0], proc_self_fd.size(), "/proc/self/fd/%d", fd); snprintf(&proc_self_fd[0], proc_self_fd.size(), "/proc/self/fd/%d", fd);
// set DUMPABLE to 1 to access /proc/self/fd
int dumpable = prctl(PR_GET_DUMPABLE, 0, 0, 0, 0);
prctl(PR_SET_DUMPABLE, 1, 0, 0, 0);
auto guard = make_scope_guard([&]() {
// restore dumpable
prctl(PR_SET_DUMPABLE, dumpable, 0, 0, 0);
});
if (readlink(&proc_self_fd[0], &buf[0], buf.size()) == -1) { if (readlink(&proc_self_fd[0], &buf[0], buf.size()) == -1) {
PRINT("readlink('%s') failed: %s [fd=%d]", &proc_self_fd[0], strerror(errno), fd); PRINT("readlink('%s') failed: %s [fd=%d]", &proc_self_fd[0], strerror(errno), fd);
return false; return false;