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Fix fallout of TOCTOU fixes for socket file non-default permissions #2195

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merged 2 commits into from
Nov 21, 2023
Merged

Fix fallout of TOCTOU fixes for socket file non-default permissions #2195

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d0df073
drivers/main.c: clarify numeric errno for faults of fstat/chmod/chown…
jimklimov Nov 20, 2023
3d86516
drivers/main.c, NEWS.adoc: fix fallout of TOCTOU fixes for socket fil…
jimklimov Nov 20, 2023
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4 changes: 4 additions & 0 deletions NEWS.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,10 @@ https://github.com/networkupstools/nut/milestone/10
activity was completed by the hardware, which led to mis-processing of
shutdown triggers. Also, notification was added to report "finished
calibration". [issue #2168, PR #2169]
* Drivers running with non-default user account (e.g. with `user=root`
in their configuration) failed to apply group ownership and permissions
to their Unix socket file for interaction with the local data server.
[#2185, #2096]

- nut-usbinfo.pl, nut-scanner and libnutscan:
* USB VendorID:ProductID support list files generated by the script for
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66 changes: 42 additions & 24 deletions drivers/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2260,6 +2260,9 @@ int main(int argc, char **argv)
/* Use file descriptor, not name, to first check and then manipulate permissions:
* https://cwe.mitre.org/data/definitions/367.html
* https://wiki.sei.cmu.edu/confluence/display/c/FIO01-C.+Be+careful+using+functions+that+use+file+names+for+identification
* Alas, Unix sockets on most systems can not be open()ed
* so there is no file descriptor to manipulate.
* Fall back to name-based "les secure" operations then.
*/
TYPE_FD fd = ERROR_FD;

Expand All @@ -2275,8 +2278,8 @@ int main(int argc, char **argv)

if (grp == NULL) {
upsdebugx(1, "WARNING: could not resolve "
"group name '%s': %s",
group, strerror(errno)
"group name '%s' (%i): %s",
group, errno, strerror(errno)
);
allOk = 0;
goto sockname_ownership_finished;
Expand All @@ -2285,59 +2288,69 @@ int main(int argc, char **argv)
mode_t mode;

if (INVALID_FD((fd = open(sockname, O_RDWR | O_APPEND)))) {
upsdebugx(1, "WARNING: opening socket file for stat/chown failed: %s",
strerror(errno)
upsdebugx(1, "WARNING: opening socket file for stat/chown failed "
"(%i), which is rather typical for Unix socket handling: %s",
errno, strerror(errno)
);
allOk = 0;
/* Can not proceed with ops below */
goto sockname_ownership_finished;
}

if (fstat(fd, &statbuf)) {
upsdebugx(1, "WARNING: stat for chown failed: %s",
strerror(errno)
if ((VALID_FD(fd) && fstat(fd, &statbuf))
|| (INVALID_FD(fd) && stat(sockname, &statbuf))
) {
upsdebugx(1, "WARNING: stat for chown of socket file failed (%i): %s",
errno, strerror(errno)
);
allOk = 0;
if (INVALID_FD(fd)) {
/* Can not proceed with ops below */
goto sockname_ownership_finished;
}
} else {
/* Maybe open() and some stat() succeeed so far */
allOk = 1;
/* Here we do a portable chgrp() essentially: */
if (fchown(fd, statbuf.st_uid, grp->gr_gid)) {
upsdebugx(1, "WARNING: chown failed: %s",
strerror(errno)
if ((VALID_FD(fd) && fchown(fd, statbuf.st_uid, grp->gr_gid))
|| (INVALID_FD(fd) && chown(sockname, statbuf.st_uid, grp->gr_gid))

Check failure

Code scanning / CodeQL

Time-of-check time-of-use filesystem race condition

The [filename](1) being operated upon was previously [checked](2), but the underlying file may have been changed since then.
) {
upsdebugx(1, "WARNING: chown of socket file failed (%i): %s",
errno, strerror(errno)
);
allOk = 0;
}
}

/* Refresh file info */
if (fstat(fd, &statbuf)) {
if ((VALID_FD(fd) && fstat(fd, &statbuf))
|| (INVALID_FD(fd) && stat(sockname, &statbuf))
) {
/* Logically we'd fail chown above if file
* does not exist or is not accessible */
upsdebugx(1, "WARNING: stat for chmod failed: %s",
strerror(errno)
upsdebugx(1, "WARNING: stat for chmod of socket file failed (%i): %s",
errno, strerror(errno)
);
allOk = 0;
} else {
/* chmod g+rw sockname */
mode = statbuf.st_mode;
mode |= S_IWGRP;
mode |= S_IRGRP;
if (fchmod(fd, mode)) {
upsdebugx(1, "WARNING: chmod failed: %s",
strerror(errno)
if ((VALID_FD(fd) && fchmod(fd, mode))
|| (INVALID_FD(fd) && chmod(sockname, mode))

Check failure

Code scanning / CodeQL

Time-of-check time-of-use filesystem race condition

The [filename](1) being operated upon was previously [checked](2), but the underlying file may have been changed since then.
) {
upsdebugx(1, "WARNING: chmod of socket file failed (%i): %s",
errno, strerror(errno)
);
allOk = 0;
}
}
}

sockname_ownership_finished:
if (VALID_FD(fd)) {
close(fd);
fd = ERROR_FD;
}

if (allOk) {
upsdebugx(1, "Group access for this driver successfully fixed");
upsdebugx(1, "Group access for this driver successfully fixed "
"(using file %s based methods)",
VALID_FD(fd) ? "descriptor" : "name");
} else {
upsdebugx(0, "WARNING: Needed to fix group access "
"to filesystem socket of this driver, but failed; "
Expand All @@ -2347,6 +2360,11 @@ int main(int argc, char **argv)
"the device: %s",
sockname);
}

if (VALID_FD(fd)) {
close(fd);
fd = ERROR_FD;
}
#else /* not WIN32 */
upsdebugx(1, "Options for alternate user/group are not implemented on this platform");
#endif /* WIN32 */
Expand Down