Differential D14467 Diff 59290 src/ioslaves/file/kauth/filehelper.cpp

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src/ioslaves/file/kauth/filehelper.cpp

Show All 15 Lines1/***
16 16​
17 You should have received a copy of the GNU Lesser General Public 17​ You should have received a copy of the GNU Lesser General Public
18 License along with this library. If not, see <http://www.gnu.org/licenses/>. 18​ License along with this library. If not, see <http://www.gnu.org/licenses/>.
19***/ 19​***/
20 20​
21#include <utime.h> 21​#include <utime.h>
22#include <fcntl.h> 22​#include <fcntl.h>
23#include <unistd.h> 23​#include <unistd.h>
24#include <dirent.h> ​
25#include <sys/stat.h> ​
26#include <errno.h> 24​#include <errno.h>
25​#include <libgen.h>
26​#include <grp.h>
27​#include <sys/stat.h>
28​#include <sys/time.h>
27 29​
28#include "filehelper.h" 30​#include "filehelper.h"
29#include "fdsender.h" 31​#include "fdsender.h"
30#include "../file_p.h" 32​#include "../file_p.h"
31 33​
34​struct OwnerId {
35​ uid_t uid;
36​ gid_t gid;
37​};
38​
39​static ActionType intToActionType(int action)
40​{
41​ switch (action) {
42​ case 1: return CHMOD;
43​ case 2: return CHOWN;
44​ case 3: return DEL;
45​ case 4: return MKDIR;
46​ case 5: return OPEN;
47​ case 6: return OPENDIR;
48​ case 7: return RENAME;
49​ case 8: return RMDIR;
50​ case 9: return SYMLINK;
51​ case 10: return UTIME;
52​ default: return UNKNOWN;
53​ }
54​}
55​
32static bool sendFileDescriptor(int fd, const char *socketPath) 56​static bool sendFileDescriptor(int fd, const char *socketPath)
33{ 57​{
34 FdSender fdSender(socketPath); 58​ FdSender fdSender(socketPath);
35 if (fdSender.isConnected() && fdSender.sendFileDescriptor(fd)) { 59​ if (fdSender.isConnected() && fdSender.sendFileDescriptor(fd)) {
36 return true; 60​ return true;
37 } 61​ }
38 return false; 62​ return false;
39} 63​}
40 64​
65​static OwnerId *getNecessaryPrivileges(ActionType action, int parent_fd, const QByteArray &baseName)
66​{
67​
68​ //for chmod, chown, utime, drop privileges to that of owner of the target file/dir
69​ //for other actions use owner of the parent directory.
70​ int target_fd = -1;
71​ if (action != CHMOD && action != CHOWN && action != UTIME) {
72​ target_fd = parent_fd;
73​ } else {
74​ target_fd = openat(parent_fd, baseName.data(), O_NOFOLLOW);
maltekUnsubmitted
Done

This is still subject to race conditions. You're opening the file with O_NOFOLLOW and calling fstat on it, correctly. But then, you don't return this file descriptor to further work on it. So there's no way to know if the file checked here and the file that's changed later on are the same.

(It's also leaking the opened file descriptor, currently.)

maltek: This is still subject to race conditions. You're opening the file with O_NOFOLLOW and calling…
75​ }
76​
77​ struct stat buf = {0};
78​ if (fstat(target_fd, &buf) == -1) {
79​ return nullptr;
80​ }
81​
82​ return new OwnerId{buf.st_uid, buf.st_gid};
83​}
84​
85​static bool dropPrivileges(OwnerId *o)
86​{
87​ if (!o) {
88​ return false;
89​ }
90​
91​ uid_t newuid = o->uid;
92​ gid_t newgid = o->gid;
93​ delete o;
94​
95​ if (newuid == 0 || newgid == 0) {
96​ return false;
97​ }
98​ //drop ancillary groups first because it requires root privileges.
99​ if (setgroups(1, &newgid) == -1) {
100​ return false;
101​ }
102​ //change real, effective, saved gid and uid.
103​ if (setregid(newgid, newgid) == -1 || setreuid(newuid, newuid) == -1) {
104​ return false;
105​ }
maltekUnsubmitted
Done

After this return false, the process is in some undefined state with unknown groups, since there is no attempt to restore the original groups. The chance of these calls failing are quite slim, however - it can only really happen due to programming error when the program doesn't have privileges to call sete[ug]id. Personally, I'd just abort the program in such circumstances, but since it should never be happening, reasonable people might disagree.

maltek: After this `return false`, the process is in some undefined state with unknown groups, since…
106​
107​ return true;
108​}
109​
41ActionReply FileHelper::exec(const QVariantMap &args) 110​ActionReply FileHelper::exec(const QVariantMap &args)
42{ 111​{
43 ActionReply reply; 112​ ActionReply reply;
44 QByteArray data = args["arguments"].toByteArray(); 113​ QByteArray data = args["arguments"].toByteArray();
45 QDataStream in(data); 114​ QDataStream in(data);
46 int action; 115​ QVariant act, arg1, arg2, arg3, arg4;
47 QVariant arg1, arg2, arg3, arg4; 116​ in >> act >> arg1 >> arg2 >> arg3 >> arg4; // act=action, arg1=source file, arg$n=dest file, mode, uid, gid, etc.
48 in >> action >> arg1 >> arg2 >> arg3 >> arg4; ​
49 117​
50 // the path of an existing or a new file/dir upon which the method will operate 118​ ActionType action = intToActionType(act.toInt());
51 const QByteArray path = arg1.toByteArray(); 119​ QByteArray tempPath1, tempPath2;
120​ tempPath1 = tempPath2 = arg1.toByteArray();
121​ const QByteArray parentDir = dirname(tempPath1.data());
122​ const QByteArray baseName = basename(tempPath2.data());
maltekUnsubmitted
Done

This needs error handling.

maltek: This needs error handling.
123​ int parent_fd = open(parentDir.data(), O_DIRECTORY | O_PATH | O_NOFOLLOW);
124​
125​ int new_parent_fd = -1;
126​ QByteArray newParentDir, newBaseName;
127​ if (action == RENAME) {
128​ tempPath1 = tempPath2 = arg2.toByteArray();
129​ newParentDir = dirname(tempPath1.data());
130​ newBaseName = basename(tempPath2.data());
131​ new_parent_fd = open(newParentDir.constData(), O_DIRECTORY | O_PATH | O_NOFOLLOW);
132​ }
133​
134​ OwnerId *oid = getNecessaryPrivileges(action, parent_fd, baseName);
135​ if (!dropPrivileges(oid)) {
136​ reply.setError(errno);
137​ }
52 138​
53 switch(action) { 139​ switch(action) {
54 case CHMOD: { 140​ case CHMOD: {
55 int mode = arg2.toInt(); 141​ int mode = arg2.toInt();
56 if (chmod(path.data(), mode) == 0) { 142​ if (fchmodat(parent_fd, baseName.data(), mode, AT_SYMLINK_NOFOLLOW) == -1) {
maltekUnsubmitted
Done

AT_SYMLINK_NOFOLLOW is not implemented for fchmodat, so this will always fail with ENOTSUP. It seems the only safe way to do this is to open() the file with O_NOFOLLOW, and then use fchmod().

maltek: AT_SYMLINK_NOFOLLOW is not implemented for fchmodat, so this will always fail with ENOTSUP. It…
57 return reply; 143​ reply.setError(errno);
58 } 144​ }
59 break; 145​ break;
60 } 146​ }
147​
61 case CHOWN: { 148​ case CHOWN: {
62 int uid = arg2.toInt(); 149​ int uid = arg2.toInt();
63 int gid = arg3.toInt(); 150​ int gid = arg3.toInt();
64 if (chown(path.data(), uid, gid) == 0) { 151​ if (fchownat(parent_fd, baseName.data(), uid, gid, AT_SYMLINK_NOFOLLOW) == -1) {
65 return reply; 152​ reply.setError(errno);
66 } 153​ }
67 break; 154​ break;
68 } 155​ }
69 case DEL: { 156​
70 if (unlink(path.data()) == 0) { 157​ case DEL:
71 return reply; 158​ case RMDIR: {
159​ int flags = 0;
160​ if (action == RMDIR) {
161​ flags |= AT_REMOVEDIR;
162​ }
163​ if (unlinkat(parent_fd, baseName.data(), flags) == -1) {
164​ reply.setError(errno);
72 } 165​ }
73 break; 166​ break;
74 } 167​ }
168​
75 case MKDIR: { 169​ case MKDIR: {
76 if (mkdir(path.data(), 0777) == 0) { 170​ int mode = arg2.toInt();
maltekUnsubmitted
Done

typo: there's a second & missing after the first condition. (I don't think it ends up affecting the result.)

maltek: typo: there's a second & missing after the first condition. (I don't think it ends up affecting…
77 return reply; 171​ if (mkdirat(parent_fd, baseName.data(), mode) == -1) {
172​ reply.setError(errno);
78 } 173​ }
maltekUnsubmitted
Done

There's no error handling here, which will likely lead to weird EBADF errors getting returned later.

maltek: There's no error handling here, which will likely lead to weird `EBADF` errors getting returned…
79 break; 174​ break;
maltekUnsubmitted
Done

For chown, dropping privileges here means that the chown later can't succeed - it's not possible to 'gift' a file to another user. I think it should be handled more like DEL/RMDIR/MKDIR etc.

maltek: For `chown`, dropping privileges here means that the `chown` later can't succeed - it's not…
chinmoyrAuthorUnsubmitted
Not Done

Ah! Since I was testing inside /opt I didn't notice. I think the order here should be: drop privilege -> change grp -> gain privilege -> change user.

chinmoyr: Ah! Since I was testing inside /opt I didn't notice. I think the order here should be: drop…
maltekUnsubmitted
Not Done

IMO, it's fine (and less complicated) to just do both in one single privileged fchmod call.

maltek: IMO, it's fine (and less complicated) to just do both in one single privileged `fchmod` call.
80 } 175​ }
81 case OPEN: { 176​
177​ case OPEN:
178​ case OPENDIR: {
maltekUnsubmitted
Not Done

I just realized that this wouldn't allow changing the owner of symbolic links. The way to go here is lchown.

maltek: I just realized that this wouldn't allow changing the owner of symbolic links. The way to go…
chinmoyrAuthorUnsubmitted
Not Done

Do you think it'll be a bad idea to skip the case for symlinks in utime, chmod, chown, for now? Right now there's no code in KIO that requires these operations to be performed on the link itself.

chinmoyr: Do you think it'll be a bad idea to skip the case for symlinks in utime, chmod, chown, for now?
maltekUnsubmitted
Not Done

Fine by me - I'm only really here to look for security problems, not to decide on which features are required for this to land.

maltek: Fine by me - I'm only really here to look for security problems, not to decide on which…
82 int oflags = arg2.toInt(); 179​ int oflags = arg2.toInt();
83 int mode = arg3.toInt(); 180​ int mode = arg3.toInt();
84 int fd = open(path.data(), oflags, mode); 181​ int extraFlag = O_NOFOLLOW;
182​ if (action == OPENDIR) {
183​ extraFlag |= O_DIRECTORY;
184​ }
185​ int fd = openat(parent_fd, baseName.data(), oflags | extraFlag, mode);
85 bool success = (fd != -1) && sendFileDescriptor(fd, arg4.toByteArray().constData()); 186​ bool success = (fd != -1) && sendFileDescriptor(fd, arg4.toByteArray().constData());
86 close(fd); 187​ close(fd);
87 if (success) { 188​ if (!success) {
88 return reply; 189​ reply.setError(errno);
89 } ​
90 break; ​
91 } ​
92 case OPENDIR: { ​
93 DIR *dp = opendir(path.data()); ​
94 bool success = false; ​
95 if (dp) { ​
96 int fd = dirfd(dp); ​
97 success = (fd != -1) && sendFileDescriptor(fd, arg4.toByteArray().constData()); ​
98 closedir(dp); ​
99 if (success) { ​
100 return reply; ​
101 } ​
102 } 190​ }
103 break; 191​ break;
104 } 192​ }
193​
105 case RENAME: { 194​ case RENAME: {
106 const QByteArray newName = arg2.toByteArray(); 195​ if (renameat(parent_fd, baseName.data(), new_parent_fd, newBaseName.constData()) == -1) {
107 if (rename(path.data(), newName.data()) == 0) { 196​ oid = getNecessaryPrivileges(action, new_parent_fd, newBaseName);
108 return reply; 197​ if (!dropPrivileges(oid) && renameat(parent_fd, baseName.data(), new_parent_fd, newBaseName.constData()) == -1) {
109 } 198​ reply.setError(errno);
110 break; ​
111 } 199​ }
112 case RMDIR: { ​
113 if (rmdir(path.data()) == 0) { ​
114 return reply; ​
115 } 200​ }
116 break; 201​ break;
117 } 202​ }
203​
118 case SYMLINK: { 204​ case SYMLINK: {
119 const QByteArray target = arg2.toByteArray(); 205​ const QByteArray target = arg2.toByteArray();
120 if (symlink(target.data(), path.data()) == 0) { 206​ if (symlinkat(target.data(), parent_fd, baseName.data()) == -1) {
121 return reply; 207​ return reply;
122 } 208​ }
123 break; 209​ break;
124 } 210​ }
211​
125 case UTIME: { 212​ case UTIME: {
126 utimbuf ut; 213​ timespec times[2];
127 ut.actime = arg2.toULongLong(); 214​ time_t actime = arg2.toULongLong();
128 ut.modtime = arg3.toULongLong(); 215​ time_t modtime = arg3.toULongLong();
maltekUnsubmitted
Done

In the error case, this attempts sending fd -1. I haven't checked the underlying code, but this will probably pollute errno with something unrelated to the underlying error.

maltek: In the error case, this attempts sending fd `-1`. I haven't checked the underlying code, but…
129 if (utime(path.data(), &ut) == 0) { 216​ times[0].tv_sec = actime * 1000;
130 return reply; 217​ times[0].tv_nsec = actime / 1000;
218​ times[1].tv_sec = modtime * 1000;
219​ times[1].tv_nsec = modtime / 1000;
maltekUnsubmitted
Done

I *think* the divisions/multiplications are reversed here.

maltek: I *think* the divisions/multiplications are reversed here.
220​ if (utimensat(parent_fd, baseName.data(), times, AT_SYMLINK_NOFOLLOW) == -1) {
221​ reply.setError(errno);
131 } 222​ }
132 break; 223​ break;
133 } 224​ }
134 }; 225​ }
135 226​
maltekUnsubmitted
Done

Somewhere here, I'd expect the privileges to be escalated again, to restore the state from before the call to dropPrivileges().

maltek: Somewhere here, I'd expect the privileges to be escalated again, to restore the state from…
136 reply.setError(errno ? errno : -1); 227​ close(parent_fd);
228​ close(new_parent_fd);
137 return reply; 229​ return reply;
138} 230​}
139 231​
140KAUTH_HELPER_MAIN("org.kde.kio.file", FileHelper) 232​KAUTH_HELPER_MAIN("org.kde.kio.file", FileHelper)
maltekUnsubmitted
Done

This early return skips all the deintialization code in the end of the function. Shouldn't it just be reply.setError(errno); like for all the other operations?

maltek: This early return skips all the deintialization code in the end of the function. Shouldn't it…