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Disable following symlinks when opening log files
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The log module used by clamd and freshclam may follow symlinks.
This is a potential security concern since the log may be owned by
the unprivileged service but may be opened by the service running as
root on startup.

For Windows, we'll define O_NOFOLLOW so the code works, though the issue
does not affect Windows.

Issue reported by Detlef.
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micahsnyder committed Sep 4, 2024
1 parent 25ca17b commit 88efeda
Showing 1 changed file with 40 additions and 11 deletions.
51 changes: 40 additions & 11 deletions common/output.c
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,12 @@

#include "output.h"

// Define O_NOFOLLOW for systems that don't have it.
// Notably, Windows doesn't have O_NOFOLLOW.
#ifndef O_NOFOLLOW
#define O_NOFOLLOW 0
#endif

#ifdef CL_THREAD_SAFE
#include <pthread.h>
pthread_mutex_t logg_mutex = PTHREAD_MUTEX_INITIALIZER;
Expand Down Expand Up @@ -304,7 +310,6 @@ int logg(loglevel_t loglevel, const char *str, ...)
char buffer[1025], *abuffer = NULL, *buff;
time_t currtime;
size_t len;
mode_t old_umask;
#ifdef F_WRLCK
struct flock fl;
#endif
Expand Down Expand Up @@ -338,18 +343,36 @@ int logg(loglevel_t loglevel, const char *str, ...)
logg_open();

if (!logg_fp && logg_file) {
old_umask = umask(0037);
if ((logg_fp = fopen(logg_file, "at")) == NULL) {
umask(old_umask);
int logg_file_fd = -1;

logg_file_fd = open(logg_file, O_WRONLY | O_CREAT | O_APPEND | O_NOFOLLOW, 0640);
if (-1 == logg_file_fd) {
char errbuf[128];
cli_strerror(errno, errbuf, sizeof(errbuf));
printf("ERROR: Failed to open log file %s: %s\n", logg_file, errbuf);

#ifdef CL_THREAD_SAFE
pthread_mutex_unlock(&logg_mutex);
#endif
printf("ERROR: Can't open %s in append mode (check permissions!).\n", logg_file);
if (len > sizeof(buffer))
if (abuffer)
free(abuffer);
return -1;
} else
umask(old_umask);
}

logg_fp = fdopen(logg_file_fd, "at");
if (NULL == logg_fp) {
char errbuf[128];
cli_strerror(errno, errbuf, sizeof(errbuf));
printf("ERROR: Failed to convert the open log file descriptor for %s to a FILE* handle: %s\n", logg_file, errbuf);

close(logg_file_fd);
#ifdef CL_THREAD_SAFE
pthread_mutex_unlock(&logg_mutex);
#endif
if (abuffer)
free(abuffer);
return -1;
}

#ifdef F_WRLCK
if (logg_lock) {
Expand All @@ -362,11 +385,16 @@ int logg(loglevel_t loglevel, const char *str, ...)
else
#endif
{
char errbuf[128];
cli_strerror(errno, errbuf, sizeof(errbuf));
printf("ERROR: Failed to lock the log file %s: %s\n", logg_file, errbuf);

#ifdef CL_THREAD_SAFE
pthread_mutex_unlock(&logg_mutex);
#endif
printf("ERROR: %s is locked by another process\n", logg_file);
if (len > sizeof(buffer))
fclose(logg_fp);
logg_fp = NULL;
if (abuffer)
free(abuffer);
return -1;
}
Expand Down Expand Up @@ -441,8 +469,9 @@ int logg(loglevel_t loglevel, const char *str, ...)
pthread_mutex_unlock(&logg_mutex);
#endif

if (len > sizeof(buffer))
if (abuffer)
free(abuffer);

return 0;
}

Expand Down

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